Covering 70% of Earth’s surface, oceans exert a major control on climate. They absorb large amounts of solar energy. Heat and water vapor are then redistributed globally through ocean currents and the circulation of the atmosphere. Jump to The Oceans
Culture, Climate Science & Education
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Principle Two: Climate is Complex
The Cultural Value is Humility
Episode Two: Rivers are Complex
Episode 2: The River is Complex
Transcript with Description of Visuals
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Audio |
Visual |
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Soft Pleasant Music |
Rylee and Alyssa Pretty On Top are walking with their grandfather on a trail through a field of tall grass to a point that overlooks the river. |
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Voice Over continues: |
Close up of the three on the overlook, looking out across the river, which lies in the canyon below. |
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My name is Rylee and I want to tell you about the lower Flathead River, the river that winds through the heart of our reservation and the heart of our culture. |
Aerial view of the lower Flathead River, a large blue-green river winding through a canyon that snakes across a prairie. Flathead Lake is in the background. |
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Salish Wake-up Song |
Teepees on the banks of the river. |
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a place to hunt and fish, a place to harvest roots and berries, |
Old black and white photo of a Pend d’Oreille man paddling a canoe on the river. |
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a place to find quiet and peace, |
Old black and white photo of a Salish woman in a beaded dress scooping water from the river into a buffalo horn. |
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and a place for song and prayer. |
Old black and white photo of a Salish woman doing beadwork at the base of a large pine tree near the river. |
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Salish Wake-up Song |
Old black and white photo of a Salish or Pend d’Oreille man fishing on the bank of the river. |
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Soft Instrumental Music |
Flying above rapids on the river, the water a clear blue-green. |
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In the 1930's, a large dam was built on tribal land. |
Old black and white photo of the dam site during construction. |
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The tribes opposed construction of the dam, which changed the habitat for our fish and wildlife on the river and damaged an area sacred to our people. |
Old black and white photo of six Indian men, some with full headdress, just below the dam. In front of them, great torrents of water flow through the gates of the dam. Then a photo giving an aerial view of the dam from the same time period. Then photo of the same Indian men standing on a boardwalk overlooking the rush of water coming out of the dam. |
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After a long battle, we were able to buy the dam. Now we manage the river's flows to reduce the impact on plants and animals. We are working hard to restore areas that the dam has harmed. |
Flying above rapids on the river, large boulders in the water. |
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Rippling Water Now we face other challenges. |
Almost eye-level with the river, which is at high flow, just below flood stage. A leafless rose bush is inundated by the flow. |
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As the climate continues to change, so does the river. Hotter temperatures in the spring lead to faster snow melt, and as a result, high levels of runoff. |
Flying just above the rushing waters of the river, which is flowing near flood stage. |
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We've come down to fish today, but the water is still too high and full of debris. In years past, the fishing was good at this time of the year. |
Alyssa and Rylee and their grandfather walking on the bank of the river. All three hold fishing poles. |
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Rylee’s Grandfather |
Close up of the three of them on the bank of the river, watching the water rushing by. |
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Rylee |
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Rylee's Grandfather Water. |
Close up of the river at eye-level. |
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This is precious stuff. You've got to respect the water. Treat it good, and it'll treat you good. So maybe the fish will wait another day for us. |
Close up of the three of them on the bank of the river, watching the water rushing by. |
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Soft Instrumental Music |
They turn to leave, walking on the trail that leads away from the river and passing by purple larkspur flowers. |
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Soft Instrumental Music |
Aerial view of the river at high flow, peaks of the snow-covered Mission Range in the background. |
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The following credits in white text over a black background: |
Principle 2
What You Need to Know About Principle 2: Climate is Complex
This principle relates to the complex interactions that drive climate processes. Interactions between land, snow and ice, living things, oceans, and the atmosphere generate things like the greenhouse effect and a number of other climate processes. The interactions are complex and require different scientific disciplines working together to understand them. Click the tabs below to learn more about the factors that regulate climate.
- Climate Varies by Region
Earth’s climate is influenced by interactions involving the Sun, ocean, atmosphere, clouds, ice, land, and life. Climate varies by region because of local differences in these interactions. Jump to Climate Varies by Region
- The Oceans
- The Atmosphere
The amount of solar energy absorbed or radiated by the Earth is moderated by the atmosphere. Greenhouse gases like water vapor, carbon dioxide, and methane occur naturally in small amounts and absorb and release heat energy. Jump to The Atmosphere
- Carbon Cycling
The abundance of greenhouse gases in the atmosphere is controlled by cycles that move carbon between the ocean, land, life, and atmosphere. Jump to Carbon Cycling
- Aerosols
Airborne particulates, called “aerosols,” have a complex effect on Earth’s energy balance: they can cause both cooling, by reflecting incoming sunlight back out to space, and warming, by absorbing and releasing heat energy into the atmosphere. Jump to Aerosols
- Feedback Loops
The interconnectedness of the Earth’s systems means that a significant change in any one part of the climate system can influence the equilibrium of the entire Earth system. Positive feedback loops can amplify these effects and trigger abrupt changes in the climate system. Jump to Feedback Loops
Principle 2a
Climate Varies by Region
click the image to enlarge the graphic
Earth’s climate is influenced by interactions involving the Sun, ocean, atmosphere, clouds, ice, land, and life. In other words, all elements of the Earth as well as important variables from space affect climate. 
Because of local differences in these interactions, climate varies by region, and that explains why the climate of the Great Plains varies.
The region is affected by several different air mass types that possess very different temperature and moisture properties. Air masses that move south over the region, from the dry, often snow-covered interior sections of central Canada, bring cold, dry air across the Plains. Air masses that form over the Gulf of Mexico and the Caribbean often move northward into the Plains with warm, very moist air. Occasionally, very warm, dry air will enter the Plains with air masses that originate in the desert areas of the southwestern United States and northern Mexico. Finally, air that originates over the Pacific Ocean will often move east, crossing the mountainous region of the western third of the United States into the Great Plains. The transport of this air up the windward side of a mountain barrier and then down the leeward side results in significant warming and drying.
Consequently, the region has a distinct north-south gradient in average temperature patterns, with a hotter south and colder north. Average annual precipitation greater than 50 inches supports lush vegetation in eastern Texas and Oklahoma. For most places, however, average rainfall is less than 30 inches, with some of Montana, Wyoming, and far west Texas receiving less than 15 inches a year. These differences are a result of the influences of oceans but also latitudinal differences, the Rocky Mountains, the atmosphere, and the land.
Temperature and Precipitation Distribution in the Great Plains
The Great Plains region has a distinct north-south gradient in average temperature patterns (left), with a hotter south and colder north. For precipitation (right), the regional gradient runs west-east, with a wetter east and a much drier west. Averages shown here are for the period 1981-2010. (Figure source: adapted from Kunkel et al. 20131).
REGIONAL CLIMATE VARIATION AND WEATHER
Source:http://discoveringantarctica.org.uk/oceans-atmosphere-landscape/atmosphere-weather-and-climate/regional-climate-variation-and-weather/
In what ways does the climate vary across Antarctica and why? What weather phenomena occur in different parts of the continent?
Warm up
There are large variations in climate across the continent owing mainly to differences in latitude, altitude, and distance from the Southern Ocean. The Antarctic climate as a whole can be discussed in terms of three different climate areas: the interior climate, the coastal climate and the climate of the Antarctic Peninsula.
The coldest and driest areas are inland, where the ice sheets form high plateaux (exceeding 4000m altitude on the East Antarctic Ice Sheet). In these areas, extremely cold air descends to create persistent high pressure that brings settled conditions with relatively low wind speeds. Temperatures during the austral summer rarely exceed -20°C and during the winter months temperatures are often around -60°C. Precipitation is usually snow in the form of ‘diamond dust’ – tiny ice crystals formed from the sublimation of water vapour in a clear, but intensely cold atmosphere – averaging less than 50mm (water equivalent) per year.
Winter at Halley research station where temperatures can drop below -50°C: a bulldozer covered in drifted snow © British Antarctic Survey, Martin Bell
Near the coast there is greater seasonal variation in temperature, and in the austral summer, temperatures can warm to around 0°C. Due to the lower altitude and latitude the air is warmer than inland, so enabling it to hold a lot more water vapour; and in addition, storm systems from the Southern Ocean have more influence. Hence, annual precipitation is much higher than inland, reaching levels of around 400mm in some coastal locations, and skies are often cloudy. Precipitation is almost always in the form of snow, with rain only falling extremely rarely in some areas in the summer months. Winds can reach high velocities in areas near the coast due to topographic factors and the phenomenon of katabatic winds discussed further below.
The Antarctic Peninsula extends into the Southern Ocean and is therefore more influenced by the sea than other parts of the continent. Annual precipitation varies greatly across the Peninsula, with some areas receiving as little as 250mm water equivalent, and other areas as much as 5000mm. Near the tip of the peninsula (which lies outside the Antarctic Circle) summer temperatures often rise a little above freezing.
Cold Facts
Regional measures of temperature and precipitation
Compared with other continents, places in Antarctica where the weather is measured regularly are few and far between (although the placement of automatic weather stations and satellite-based weather measurements are improving coverage of the continent). Of the weather stations that exist, most have relatively short records. As noted in Key factors behind Antarctica’s climate, strict conditions need to be met for weather recordings to be classed as ‘official’ for statistical purposes, and climatologists like to base any statements about the climate of an area (the ‘average weather’ experienced at a locality) on at least 30 years of data (the ’30 year mean’). There are, however, some stations in Antarctica that meet these stringent requirements and allow scientists to build up a picture of how temperature, precipitation, and other climate measures vary across the continent. A few stations have records extending back well beyond 30 years, and these stations are crucial for studies of climate change as described in Climate change: past and future.
Important stations where weather is recorded in the interior of the continent include the Amundsen-Scott station (USA) at the South Pole and the Vostok station (Russia) in East Antarctica. Both stations were established in 1957 as part of the International Geophysical Year. The Amundsen-Scott station is at an elevation of 2900m above sea level and the Vostok station is at 3500m. In addition to being very cold, these stations also represent the extreme of the polar desert climate with very low levels of humidity and precipitation. Weather conditions characteristic of coastal areas of the continent are represented at Halley station (UK) bordering the Weddell Sea, which has been in operation since 1956 and McMurdo station (USA) bordering the Ross Sea, also started in 1956. Also on the coast, the Mawson station (Australia) was set up in 1954 and is the oldest continuously occupied station inside the Antarctic Circle. This station is also notable for the force of the katabatic winds (explained below) that come down off of the high ice sheet: gusts of wind here can sometimes be over 100mph. The Rothera station (UK) provides data on the climate of the Antarctic Peninsula. It is located on the west side of the peninsula at Rothera Point on Adelaide Island and has been in operation since 1975. Peninsula weather recordings have been taken over a longer period of time at Vernadsky station (Ukraine) which was previously a British station called Faraday (the climate data are sometimes referred to as being from Faraday/Vernadsky). There are also other stations along the Peninsula, notably the Palmer station (USA) and the San Martin station (Argentina). There are stations on several islands off the coast of Antarctica that provide data on the weather and climate of the Southern Ocean, for example Signy station (UK) on Signy Island in the South Orkney Islands, first occupied in 1947. Data from a selection of stations are contained in the spreadsheet attached to Student activity 2 below.
Find out the current weather conditions at various stations at the British Antarctic Survey
Winds
The dominant pattern of atmospheric circulation over Antarctica involves cold air sinking in the interior and then moving away from this area of high pressure towards the edges of the continent. The air that sinks down onto the interior is replaced by air from aloft that has travelled southwards at a higher altitude. This large-scale circulation of air is often referred to as the polar cell. (There is also a polar cell in the Arctic.) As air from the interior moves outwards across Antarctica, it doesn’t travel directly from south to north. Instead, the direction of the air is deflected by the Earth’s rotation to form polar easterlies, meaning that the prevailing wind direction is from east to west across much of the continent. This occurs because the Coriolis Force causes air to be deflected to the left of its ‘pressure gradient path’ (the most direct route from high to low pressure) in the Southern Hemisphere.
Where these easterly winds approach the coast they can reach high velocities. A katabatic wind refers to cold and relatively dense air near the surface moving downhill due to gravity. Across much of the gently sloping ice sheet katabatic winds average about 10 miles per hour; but towards the edges of the continent, slope gradients become steep and air can be funnelled down into coastal valleys causing much higher average velocities. In some places the average annual wind velocity is nearly 50 miles per hour!
High winds make life difficult at a field camp, Rutford Ice Stream © British Antarctic Survey, David Vaughan
Moving northwards, away from the continental interior, the polar easterlies eventually give way to the zone of westerly winds affecting the Southern Ocean. The westerly winds are associated with the low pressure area (circumpolar trough) that surrounds the continent owing to the large temperature difference between cold polar air and milder air from the southern mid-latitudes. The circumpolar trough exists because where warmer air meets the cold polar air (along the polar front) the warmer air is forced upwards, creating lower pressure at sea level and the frequent storm systems that affect the Southern Ocean. Air moving from the mid-latitudes towards the circumpolar trough is deflected to the left by the Coriolis force thereby producing the westerly prevailing winds. The westerly winds and Southern Ocean storm systems affect parts of the Antarctic coastline, the Antarctic Peninsula, and the islands off the coast of Antarctica.
Other weather phenomena
Antarctica is also known for several intriguing types of atmosphere and weather phenomena.
Aurora Australis
Known as the Aurora borealis in the Northern Hemisphere, this spectacular phenomenon is often described as waving or shimmering curtains of light across the night sky. It is caused by charged particles from the Sun being pulled towards the Earth’s magnetic poles and interacting with gases high in the atmosphere to illuminate the night sky.
Aurora Australis at Halley Research Station © British Antarctic Survey, Thomas Speiss
Diamond dust
This occurs when water vapour sublimates directly out of the cold atmosphere to form ice crystals, creating a form of precipitation that occurs under clear skies.
Halo
This optical phenomenon occurs frequently in Antarctica because of ice crystals in the atmosphere that reflect and refract light. Halos are typically rings of light circling the Sun or Moon, but they can also appear as pillars and arcs of light.
A sun halo above the Laws Platform at Halley V Research Station © British Antarctic Survey, Agnieszka Fryckowska
Whiteout
Under whiteout conditions, it is difficult to judge distances, perceive gradients or make out the horizon. Whiteouts can occur under different weather conditions (for example blizzards or calm, overcast conditions) where light is diffuse and it is hard to distinguish the surface from the sky.
Q
Principle 2b
The Oceans
Covering 70% of the Earth's surface, the oceans exert a major control on climate by dominating Earth's energy and water cycles.
Oceans have the capacity to absorb large amounts of solar energy. Heat and water vapor are redistributed globally through ocean currents and atmospheric circulation.
Changes in ocean circulation caused by tectonic movements or large influxes of fresh water from melting polar ice can lead to large and even abrupt changes in climate, both locally and on global scales.
click the graphic to enlarge it
Annual global sea-surface temperature anomalies from 1880 to 2015.
This graph shows how much ocean temperatures have risen since 1880. Each bar represents how much the temperature in a given year was above or below the average of the base period (1951 to 1980). Red is positive (how much the temperature was above the average), blue is negative (how much the temperatures was below the average). From: http://www.ncdc.noaa.gov/cag/time-series/global/globe/ocean/ytd/12/1880-2016.
click the graphic to enlarge it
The global ocean conveyor belt.
The global ocean conveyor belt is a constantly moving system of deep-ocean circulation driven by temperature and salinity. The great ocean conveyor moves water around the globe. Cold, salty water is dense and sinks to the bottom of the ocean while warm water is less dense and remains on the surface. The conveyor belt plays an enormous role in regulating Earth's climate.
By Brian Kahn
Move over polar bears. Are starving sea lion pups the new face of climate change?
This year’s slew of hungry pups washing ashore in California, which has generated a slew of media coverage replete with heart-tugging images, has roots in natural temperature fluctuations in the ocean. But in the coming decades, human-induced warming could make these types of conditions more common. And sea lion pups are just the tip of a larger shift in the Pacific and the rest of the world’s oceans if human emissions continue to warm the planet. Read more…
The West Coast Is in Hot Water
By Brian Kahn
Move over polar bears. Are starving sea lion pups the new face of climate change?
This year’s slew of hungry pups washing ashore in California, which has generated a slew of media coverage replete with heart-tugging images, has roots in natural temperature fluctuations in the ocean. But in the coming decades, human-induced warming could make these types of conditions more common. And sea lion pups are just the tip of a larger shift in the Pacific and the rest of the world’s oceans if human emissions continue to warm the planet.
In recent weeks, emaciated young sea lions have been washing up on California beaches (though a few healthy ones have also shown up, including one who got to hang ten with a local surfer). Roughly 1,800 stranded pups have been found on California beaches through the first two-and-a-half months of 2015. That’s well above the 100 or so that usually turn up through the end of March and “at least as high as anything in the historical record,” according to Nate Mantua, a scientist at the Southwest Fisheries Science Center in La Jolla, Calif.
In 2013 and 2014, large numbers of disheveled sea lion pups were also stranded on California’s beaches, though not at the same levels as this year. One of the main causes has been the unusual and in some cases, record setting — warm water off the West Coast of the U.S. and stretching all the way to the Gulf of Alaska. The warm water is less rich in nutrients and the types of microscopic organisms and fish upon which sea lions usually feed. That has forced sea lion moms and pups alike to forage further for food, a tiring proposition for young sea lions.
While the sea lions have been the face of the recent intrusion of warm water, ecosystem disruptions are visible throughout the stretch of the eastern Pacific and Gulf of Alaska. Cold water copepods — small crustaceans at the base of the food chain — populations have dropped off sharply in the past year, while their warm water (less nutritious) brethren have shown up in huge quantities.
Further up the food chain, skipjack tuna have turned up in Alaska, thousands of miles beyond their usual range and Mantua said, “sportfish like marlin — things people travel to fish for in Baja — they’re catching them for day trips in southern California.”
Beyond the recent slew of strange sightings, Mantua warned that the impacts will linger over at least the next 2-3 years even if waters cool. He said juvenile salmon that have headed to sea are finding less hospitable waters, lowering their survival rates and reducing catches when they spawn back upriver.
West Coast commercial fisheries, including Alaska, brought in $2.7 billion in 2013, roughly half of the U.S. total that year. All these species shifts are likely to have ripple effects on local coastal communities that rely on them for livelihoods.
“Fisheries, they’ve already seen it,” Mantua said, though the exact economic impacts have yet to be quantified.
The warm water in the eastern Pacific over the past two years is a harbinger of things to come for the region. Ocean temperatures have been rising around the world and are expected to keep warming, and the eastern Pacific could see the odd conditions of the past two years become commonplace by mid-century. Just how far-reaching the impacts will be and which species will adapt and which will fail to is something scientists are still trying to untangle.
Monthly sea surface temperature anomalies. The red box outlines the origins of what Washington state climatologist Nick Bond has termed "the blob" of warm water. Credit: IRI Data Library
The causes for the current eastern Pacific warm temperatures — what Washington state climatologist Nick Bond has coined "the blob" — are not fully known, but are most likely natural. The blob has spread across an expanse of water 1,000 miles across with above-normal water temperatures running from the surface to as deep as 300 feet.
While human-induced warming is heating seas around the world, Bond said that’s not the main cause for this particular hot spot.
“It’s mostly a fluke of climate variability,” Bond said. “At least part of it can be linked to deep convection in the far western tropical Pacific.”
Mantua said the ridge that has kept California dry has also helped lock warm water into place and spread.
There’s also a chance that the warmth could mark a shift to the positive phase of a climate pattern called the Pacific Decadal Oscillation (PDO). That pattern is characterized by warm water along the West Coast, which would further hurt certain fisheries, particularly salmon in the Northwest. A positive PDO would also likely ramp up global temperatures.
Yet the natural variations behind this warming have researchers like Bond and Mantua paying close attention to what happens to everything from humble plankton to large predators.
“While the causes of the warm waters (today) are not the same as what the causes will be in the 2040s or 2050s, how it plays out in the ecosystems, how it works through the food chain, there may be some real parallels there,” Bond said.
The Pacific Northwest has already shown a willingness and ability to adapt to ocean acidification, which threatened to destroy its oyster industry in the mid-2000s. Despite continuing high rates of acidification in the region, the risks its poses to livelihoods are relatively low compared other parts of the U.S.
The connectedness of the ocean and climate also has scientists looking outside the region for clues of how the future will unfold.
“We know the tropical ocean temperatures in the western Pacific and Indian Oceans have long-term sustained warming trends,” Mantua said, noting that these parts of the ocean will be first to see a global warming signal. “So are they starting to disrupt historical climate patterns because they’re going into new territory? That’s what people are looking at right now.”
Source: http://www.climatecentral.org/news/the-west-coast-is-in-hot-water-18813
Ocean circulation
Published: June 7, 2007, 1:14 am
Updated: March 26, 2013, 3:33 pm
Author: Michael Pidwirny
Source: http://editors.eol.org/eoearth/wiki/Ocean_currents
Ocean Circulation Conveyor Belt. The ocean plays a major role in the distribution of the planet's heat through deep sea circulation. This simplified illustration shows this "conveyor belt" circulation which is driven by the difference in heat and salinity
Surface Ocean Currents
An ocean current can be defined as a horizontal movement of seawater in the ocean. Ocean currents are driven by the circulation of wind above surface waters, interacting with evaporation, sinking of water at high latitudes, and the Coriolis force generated by the earth's rotation. Frictional stress at the interface between the ocean and the wind causes the water to move in the direction of the wind. Large surface ocean currents are a response of the atmosphere and ocean to the flow of energy from the tropics to polar regions. In some cases, currents are transient features and affect only a small area. Other ocean currents are essentially permanent and extend over large horizontal distances.
On a global scale, large ocean currents are constrained by the continental masses found bordering the three oceanic basins. Continental borders cause these currents to develop an almost closed circular pattern called a gyre. Each ocean basin has a large gyre located at approximately 30° North and one at 30° South latitude in the subtropical regions. The currents in these gyres are driven by the atmospheric flow produced by the subtropical high pressure systems. Smaller gyres occur in the North Atlantic and Pacific Oceans centered at 50° North. Currents in these systems are propelled by the circulation produced by polar low pressure centers. In the Southern Hemisphere, these gyre systems do not develop because of the lack of constraining land masses.
A typical gyre displays four types of joined currents: two east-west aligned currents found respectively at the top and bottom ends of the gyre; and two boundary currents oriented north-south and flowing parallel to the continental margins. Direction of flow within these currents is determined by the direction of the macro-scale wind circulation interacting with the Coriolis force. Boundary currents play a role in redistributing global heat latitudinally.
Surface Currents of the Subtropical Gyres
On either side of the equator, in all ocean basins, there are two west-flowing currents: the North and South Equatorial (Figure 1). These currents flow between 3 and 6 kilometers per day and usually extend 100 to 200 meters in depth below the ocean surface. The Equatorial Counter Current, which flows towards the east, is a partial return of water carried westward by the North and South Equatorial currents. In El Niño years, this current intensifies in the Pacific Ocean.
Flowing from the equator to high latitudes are the western boundary currents. These warm water currents have specific names associated with their location: North Atlantic - Gulf Stream; North Pacific - Kuroshio; South Atlantic - Brazil; South Pacific - East Australia; and Indian Ocean - Agulhas. All of these currents are generally narrow, jet-like flows that travel at speeds between 40 and 120 kilometers per day. Western boundary currents are the deepest ocean surface flows, usually extending 1,000 meters below the ocean surface.
Flowing from high latitudes to the equator are the eastern boundary currents. These cold water currents also have specific names associated with their location: North Atlantic - Canary; North Pacific - California; South Atlantic - Benguela; South Pacific - Peru; and Indian Ocean - West Australia. All of these currents are generally broad, shallow moving flows that travel at speeds between 3 and 7 kilometers per day.
In the Northern Hemisphere, the east-flowing North Pacific Current and North Atlantic Drift move the waters of western boundary currents to the starting points of the eastern boundary currents. The South Pacific Current, South Indian Current and South Atlantic Current provide the same function in the Southern Hemisphere. These currents are associated with the Antarctic Circumpolar Current (West Wind Drift). Because of the absence of landmass at this latitude zone, the Antarctic Circumpolar flows in continuous fashion around Antarctica and only provides a partial return of water to the three Southern Hemispheric ocean basins.
Surface Currents of the Polar Gyres
The polar gyres exist only in the Atlantic and Pacific basins in the Northern Hemisphere. They are propelled by the counterclockwise winds associated with the development of permanent low pressure centers at 50° of latitude over the ocean basins. Note that the west-flowing current forming the southern margin of the polar gyres is also the eastward-flowing flowing current forming the northen margin of the subtropical gyres. Other currents associated with these gyres are shown on Figure 1.
Subsurface Currents
Figure 2: The following illustration describes the flow pattern of the major subsurface ocean currents. Near surface warm currents are drawn in red. Blue depicts the deep cold currents. Note how this system is continuously moving water from the surface to deep within the oceans and back to the top of the ocean. (Source: Arctic Climate Impact Assessment (ACIA)).
The world's oceans also have significant currents that flow beneath the surface (Figure 2). Subsurface currents generally travel at a much slower speed when compared to surface flows. The subsurface currents are driven by differences in the density of seawater. The density of seawater deviates in the oceans because of variations in temperature and salinity. Near-surface seawater begins its travel deep into the ocean in the North Atlantic. The downwelling of this water is caused by high levels of evaporation that cool and increase the salinity of the seawater as it flows poleward. The downwelling (sinking) of this cold, dense, saline water takes place between Northern Europe and Greenland and just north of of Labrador, Canada. This seawater then moves south at depth along the coast of North and South America until it reaches Antarctica. At Antarctica, the cold and dense seawater then travels eastward joining another deep current that is created by evaporation and sinking occuring between Antarctica and the southern tip of South America. Slightly into its eastward voyage, the deep cold flow splits off into two currents, one of which moves northward. In the North Pacific and in the northern Indian Ocean, these two currents are drawn up from the ocean floor to its surface by wind-induced upwelling. The water warms at the surface and forms a current that flows at the surface eventually back to the starting point in the North Atlantic, or creating a shallow flow that circles around Antarctica. One complete circuit of this flow of seawater is estimated to take about 1,000 years.
Citation
Pidwirny, M. (2013). Ocean circulation. Retrieved from http://www.eoearth.org/view/article/154990
For another, more extensive article on the oceans and climate, click here.
Q
Soaring ocean temperature is 'greatest hidden challenge of our generation'
IUCN report warns that ‘truly staggering’ rate of warming is changing the behaviour of marine species, reducing fishing zones and spreading disease
Source: https://www.theguardian.com/environment/2016/sep/05/soaring-ocean-temperature-is-greatest-hidden-challenge-of-our-generation
The scale of warming in the ocean is ‘truly staggering’, the report warns. Photograph: Ralph Lee Hopkins/Alamy
Oliver Milman in Honolulu
The soaring temperature of the oceans is the “greatest hidden challenge of our generation” that is altering the make-up of marine species, shrinking fishing areas and starting to spread disease to humans, according to the most comprehensive analysis yet of ocean warming.
The oceans have already sucked up an enormous amount of heat due to escalating greenhouse gas emissions, affecting marine species from microbes to whales, according to an International Union for Conservation of Nature (IUCN) report involving the work of 80 scientists from a dozen countries.
The profound changes underway in the oceans are starting to impact people, the report states. “Due to a domino effect, key human sectors are at threat, especially fisheries, aquaculture, coastal risk management, health and coastal tourism.”
Dan Laffoley, IUCN marine adviser and one of the report’s lead authors, said: “What we are seeing now is running well ahead of what we can cope with. The overall outlook is pretty gloomy.
“We perhaps haven’t realised the gross effect we are having on the oceans, we don’t appreciate what they do for us. We are locking ourselves into a future where a lot of the poorer people in the world will miss out.”
The scale of warming in the ocean, which covers around 70% of the planet, is “truly staggering”, the report states. The upper few metres of ocean have warmed by around 0.13C a decade since the start of the 20th century, with a 1-4C increase in global ocean warming by the end of this century.The ocean has absorbed more than 90% of the extra heat created by human activity. If the same amount of heat that has been buried in the upper 2km of the ocean had gone into the atmosphere, the surface of the Earth would have warmed by a devastating 36C, rather than 1C, over the past century.
Global sea surface temperatures are currently at their highest level since records began
Annual global sea surface temperature anomalies in degrees celsius
-0.500.5188019031926194919721995
At some point, the report says, warming waters could unlock billions of tonnes of frozen methane, a powerful greenhouse gas, from the seabed and cook the surface of the planet. This could occur even if emissions are drastically cut, due to the lag time between emitting greenhouse gases and their visible consequences.
Warming is already causing fish, seabirds, sea turtles, jellyfish and other species to change their behaviour and habitat, it says. Species are fleeing to the cooler poles, away from the equator, at a rate that is up to five times faster than the shifts seen by species on land.
Even in the north Atlantic, fish will move northwards by nearly 30km per decade until 2050 in search of suitable temperatures, with shifts already documented for pilchard, anchovy, mackerel and herring.
The warming is having its greatest impact upon the building blocks of life in the seas, such as phytoplankton, zooplankton and krill. Changes in abundance and reproduction are, in turn, feeding their way up the food chain, with some fish pushed out of their preferred range and others diminished by invasive arrivals.
With more than 550 types of marine fishes and invertebrates already considered threatened, ocean warming will exacerbate the declines of some species, the report also found.
The movement of fish will create winners and losers among the 4.3 billion people in the world who rely heavily upon fish for sustenance. In south-east Asia, harvests from fisheries could drop by nearly a third by 2050 if emissions are not severely curtailed. Global production from capture fisheries has already levelled off at 90m tonnes a year, mainly due to overfishing, at a time when millions more tonnes will need to be caught to feed a human population expected to grow to 9 billion by 2050.
Humans are also set to suffer from the spread of disease as the ocean continues to heat up. The IUCN report found there is growing evidence of vibrio bacterial disease, which can cause cholera, and harmful algal bloom species that can cause food poisoning. People are also being affected by more severe, if not more numerous, hurricanes due to the extra energy in the ocean and atmosphere.
Coral reefs, which support around a quarter of all marine species, are suffering from episodes of bleaching that have increased three-fold over the past 30 years. This bleaching occurs when prolonged high temperatures cause coral to expel its symbiotic algae, causing it to whiten and ultimately die, such as the mass mortality that has gripped the Great Barrier Reef.
Ocean acidification, where rising carbon dioxide absorption increases the acidity of the water, is making it harder for animals such as crabs, shrimps and clams to form their calcium carbonate shells.
The IUCN report recommends expanding protected areas of the ocean and, above all, reduce the amount of heat-trapping gases pumped into the atmosphere.
“The only way to preserve the rich diversity of marine life, and to safeguard the protection and resources the ocean provides us with, is to cut greenhouse gas emissions rapidly and substantially,” said Inger Andersen, director general of the IUCN.
Q
Principle 2c
The Atmosphere
Our atmosphere effects the amount of solar energy absorbed by the Earth and the amount of that energy that the Earth radiates back out into space. 
Greenhouse gases — water vapor, carbon dioxide, and methane — occur naturally in small amounts in our atmosphere. They absorb and release heat energy more efficiently than other gases like nitrogen and oxygen, which are actually more abundant.
Indeed, the greenhouse gases are so efficient that even a small increase in their concentration can have an enormous effect on our climate. Human released CO2 and methane are two greenhouse gases that are dramatically changing Earth’s climate. Read more…
The Atmosphere
Our atmosphere effects the amount of solar energy absorbed by the Earth and the amount of that energy that the Earth radiates back out into space. In the 1800s, scientist John Tyndall was studying the energy balance of the Earth, looking at incoming solar energy, primarily short-wave ultraviolet and visible light, and measuring that against outgoing infrared heat from the Earth after it has absorbed the energy from the sun. Tyndall set up an atmospheric laboratory in the basement of the Royal Institute in London and began experimenting with various trace gases in the atmosphere to determine their radiant properties. The primary gases in air— nitrogen (79%), oxygen (21%), and argon (~1%) — make up 99.9% of the gas in the atmosphere. But none of them absorb light and re-radiate infrared heat. Through his experiments, Tyndall determined that two gases in particular, water vapor (H2O) and carbon dioxide (CO2) do absorb light and re-radiate heat. He published his findings in 1872. From this research the concept of the “Greenhouse Effect” as an important component of the Earth’s energy balance was developed—so we have known about the greenhouse effect at least since then. Tyndall’s laboratory experiments contribute to today’s detailed understanding of how solar energy drives the Earth’s climate system.
Greenhouse gases — water vapor, carbon dioxide, and methane — occur naturally in small amounts in our atmosphere. They absorb and release heat energy more efficiently than other gases like nitrogen and oxygen, which are actually more abundant.
Indeed, the greenhouse gases are so efficient that even a small increase in their concentration can have an enormous effect on our climate. Human released CO2 and methane are two greenhouse gases that are dramatically changing Earth’s climate.With the setup below, Tyndall observed new chemical reactions produced by high frequency light waves acting on certain vapors. This work help lead to his discovery of the greenhouse effect.
Atmospheric composition
Published: July 14, 2010, 12:11 am
Updated: April 4, 2013, 5:45 pm
Author: Michael Pidwirny
Table 1 lists the eleven most abundant gases found in the Earth's lower atmosphere by volume. Of the most abundant, nitrogen, oxygen, water vapor, carbon dioxide, methane, nitrous oxide, and ozone are extremely important to the health of the Earth's biosphere.
The table indicates that nitrogen and oxygen are the main components of the atmosphere by volume. Together these two gases make up approximately 99% of the dry atmosphere. Both of these gases have very important associations with life. Nitrogen is removed from the atmosphere and deposited at the Earth's surface mainly by specialized nitrogen fixing bacteria, and by way of lightning through precipitation. The addition of this nitrogen to the Earth's surface soils and various water bodies supplies much needed nutrition for plant growth. Nitrogen returns to the atmosphere primarily through biomass combustion and denitrification.
Oxygen is exchanged between the atmosphere and life through the processes of photosynthesis and respiration. Photosynthesis produces oxygen when carbon dioxide and water are chemically converted into glucose with the help of sunlight. Respiration is the opposite process of photosynthesis. In respiration, oxygen is combined with glucose to chemically release energy for metabolism. The products of this reaction are water and carbon dioxide.
Figure 1:Global distribution of water vapor for January 2003 from the Earth's surface to the top of the atmosphere as measured in millimeters of precipitable water. During January, the atmosphere contains low amounts of water vapor over the continents of North America and Eurasia which are experiencing winter. The highest concentrations of water vapor are found over the equator, Brazil, Indonesia, northern Australia, the Indian Ocean, and the western side of South Pacific Ocean at the tropics and subtropics.(Source: NASA's Atmospheric Infrared Sounder)
The next most abundant gas on the table is water vapor. Water vapor varies in concentration in the atmosphere both spatially and temporally (see Figures 1 and 2). The highest concentrations of water vapor are found near the equator over the oceans and tropical rain forests. Cold polar areas and subtropical continental deserts are locations where the volume of water vapor can approach zero percent. Water vapor has several very important functional roles on our planet:
The fifth most abundant gas in the atmosphere is carbon dioxide. The volume of this gas has increased by over 35% in the last three hundred years (see Figure 3). This increase is primarily due to human activities such as combustion of fossil fuels, deforestation, and other forms of land-use change. Some scientists believe that this increase is causing global warming through an enhancement of the greenhouse effect. Carbon dioxide is also exchanged between the atmosphere and life through the processes of photosynthesis and respiration.
Figure 2:Global distribution of water vapor for July 2003 from the Earth's surface to the top of the atmosphere as measured in millimeters of precipitable water. Compared to the month of January, the continents of North America and Eurasia see a significant increase in atmospheric water vapor. Areas with the highest concentrations of water vapor are found over the equator, India, southeast Asia, the Indian Ocean, the Gulf of Mexico, central Africa, western side of the North Pacific Ocean at the tropics and subtropics, and along the east coast of the USA. (Source: NASA's Atmospheric Infrared Sounder)
Methane is a very strong greenhouse gas. Since 1750, methane concentrations in the atmosphere have increased by more than 150%. The primary sources for the additional methane added to the atmosphere (in order of importance) are: rice cultivation; domestic grazing animals; termites; landfills; coal mining; and oil and gas extraction. Anaerobic conditions associated with rice paddy flooding results in the formation of methane gas. However, an accurate estimate of how much methane is being produced from rice paddies has been difficult to ascertain. More than 60% of all rice paddies are found in India and China where scientific data concerning emission rates are unavailable. Nevertheless, scientists believe that the contribution of rice paddies is large because this form of crop production has more than doubled since 1950. Grazing animals release methane to the environment as a result of herbaceous digestion. Some researchers believe the addition of methane from this source has more than quadrupled over the last century. Termites also release methane through similar processes. Land-use change in the tropics, due to deforestation, ranching, and farming, may be causing termite numbers to expand. If this assumption is correct, the contribution from these insects may be important. Methane is also released from landfills, coal mines, and gas and oil drilling. Landfills produce methane as organic wastes decompose over time. Coal, oil, and natural gas deposits release methane to the atmosphere when these deposits are excavated or drilled.
The average concentration of the greenhouse gas nitrous oxide is now increasing at a rate of 0.2 to 0.3% per year. Its part in the enhancement of the greenhouse effect is minor relative to the other greenhouse gases already mentioned. However, it does have an important role in the artificial fertilization of ecosystems. In extreme cases, this fertilization can lead to the death of forests, eutrophication of aquatic habitats, and species exclusion. Sources for the increase of nitrous oxide in the atmosphere include: land-use conversion; fossil fuel combustion; biomass burning; and soil fertilization. Most of the nitrous oxide added to the atmosphere each year comes from deforestation and the conversion of forest, savanna and grassland ecosystems into agricultural fields and rangeland. Both of these processes reduce the amount of nitrogen stored in living vegetation and soil through the decomposition of organic matter. Nitrous oxide is also released into the atmosphere when fossil fuels and biomass are burned. However, the combined contribution to the increase of this gas in the atmosphere is thought to be minor. The use of nitrate and ammonium fertilizers to enhance plant growth is another source of nitrous oxide, yet how much is released from this process has been difficult to quantify. Estimates suggest that the contribution from this source represents from 50% to 0.2% of nitrous oxide added to the atmosphere annually.
Figure 3: Changing Content of Carbon Dioxide in the Earth's Atmosphere. The following graph illustrates the rise in atmospheric carbon dioxide from 1744 to 2005. Note that the increase in carbon dioxide's concentration in the atmosphere has been exponential during the period examined. An extrapolation into the immediate future would suggest continued increases. (Source: PhysicalGeography.net)
Ozone's role in the enhancement of the greenhouse effect has been difficult to determine. Accurate measurements of past long-term (more than 25 years in the past) levels of this gas in the atmosphere are currently unavailable. Moreover, concentrations of ozone gas are found in two different regions of the Earth's atmosphere. The majority of the ozone (about 97%) found in the atmosphere is concentrated in the stratosphere at an altitude of 15 to 55 kilometers above the Earth's surface. This stratospheric ozone provides an important service to life on the Earth as it absorbs harmful ultraviolet radiation. In recent years, levels of stratospheric ozone have been decreasing due to the buildup of human-created chlorofluorocarbons in the atmosphere. Since the late 1970s, scientists have noticed the development of severe holes in the ozone layer over Antarctica. Satellite measurements have indicated that the zone from 65° North to 65° South latitude has had a 3% decrease in stratospheric ozone since 1978.
Ozone is also highly concentrated at the Earth's surface in and around cities. Most of this ozone is created as a byproduct of human-created photochemical smog. This buildup of ozone is toxic to organisms living at the Earth's surface.
Citation
Pidwirny, M. (2013). Atmospheric composition. Retrieved from http://www.eoearth.org/view/article/150296
- See more at: http://www.eoearth.org/view/article/150296/#sthash.gMGIJDaL.dpuf
Q
Greenhouse effect
Published: September 17, 2008, 4:48 pm
Updated: July 17, 2012, 8:52 pm
Author: Michael Pidwirny
Figure 1: As illustrated in the diagram above, of all the sunlight that passes through the atmosphere annually, only 51% is available at the Earth's surface to do work. This energy is used to heat the Earth's surface and lower atmosphere, melt and evaporate water, and run photosynthesis in plants. Of the other 49%, 4% is reflected back to space by the Earth's surface, 26% is scattered or reflected to space by clouds and atmospheric particles, and 19% is absorbed by atmospheric gases and clouds. (Source: PhysicalGeography.net)
The greenhouse effect is a naturally occurring process that aids in heating the Earth's surface and atmosphere. It results from the fact that certain atmospheric gases, such as carbon dioxide, water vapor, and methane, are able to change the energy balance of the planet by absorbing longwave radiation emitted from the Earth's surface. Without the greenhouse effect life on this planet would probably not exist as the average temperature of the Earth would be a chilly -18° Celsius, rather than the present 15° Celsius.
As energy from the sun passes through the atmosphere a number of things take place (see Figure 1). A portion of the energy (26% globally) is reflected or scattered back to space by clouds and other atmospheric particles. About 19% of the energy available is absorbed by clouds, gases (like ozone), and particles in the atmosphere. Of the remaining 55% of the solar energy passing through the Earth's atmosphere, 4% is reflected from the surface back to space. On average, about 51% of the sun's radiation reaches the surface. This energy is then used in a number of processes, including the heating of the ground surface; the melting of ice and snow and the evaporation of water; and plant photosynthesis.
Figure 2: The diagram above illustrates the greenhouse effect. This process begins with the absorption of shortwave radiation from the sun. Absorption causes the solar energy to be converted into sensible heat at the Earth's surface. Some of this heat is transferred to the lower atmosphere by conduction and convection. After the heating of the ground and the lower atmosphere, these surfaces become radiators of infrared or longwave radiation and they begin to cool. This emission of energy is directed to space. However, only a portion of this energy actually makes it through the atmosphere. About 70% of the longwave radiation emitted from the Earth's surface is absorbed by the atmosphere's greenhouse gases. (Source: PhysicalGeography.net)
The heating of the ground by sunlight causes the Earth's surface to become a radiator of energy in the longwave band (sometimes called infrared radiation). This emission of energy is generally directed to space (see Figure 2). However, only a small portion of this energy actually makes it back to space. The majority of the outgoing infrared radiation is absorbed by the greenhouse gases (see Figure 3).
Absorption of longwave radiation by the atmosphere causes additional heat energy to be added to the Earth's atmospheric system. The now warmer atmospheric greenhouse gas molecules begin radiating longwave energy in all directions. Over 90% of this emission of longwave energy is directed back to the Earth's surface where it once again is absorbed by the surface. The heating of the ground by the longwave radiation causes the ground surface to once again radiate, repeating the cycle described above, again and again, until no more longwave is available for absorption.
Figure 3: Annual (1987) quantity of outgoing longwave radiation absorbed in the atmosphere. Image created by the CoVis Greenhouse Effect Visualizer. (Source: PhysicalGeography.net)
The amount of heat energy added to the atmosphere by the greenhouse effect is controlled by the concentration of greenhouse gases in the Earth's atmosphere. All of the major greenhouse gases have increased in concentration since the beginning of the Industrial Revolution (about 1700 AD). As a result of these higher concentrations, scientists predict that the greenhouse effect will be enhanced and the Earth's climate will become warmer. Predicting the amount of warming is accomplished by computer modeling. Computer models suggest that a doubling of the concentration of the main greenhouse gas, carbon dioxide, may raise the average global temperature between 1 and 3° Celsius. However, the numeric equations of computer models do not accurately simulate the effects of a number of possible negative feedbacks. For example, many of the models cannot properly simulate the negative effects that increased cloud cover would have on the radiation balance of a warmer Earth. Increasing the Earth's temperature would cause the oceans to evaporate greater amounts of water, causing the atmosphere to become cloudier. These extra clouds would then reflect a greater proportion of the sun's energy back to space reducing the amount of solar radiation absorbed by the atmosphere and the Earth's surface. With less solar energy being absorbed at the surface, the effects of an enhanced greenhouse effect may be counteracted.
A number of gases are involved in the human-caused enhancement of the greenhouse effect (see Table 1). These gases include: carbon dioxide (CO2); methane (CH4); nitrous oxide (N2O); chlorofluorocarbons (CFXClX); and tropospheric ozone (O3). Of these gases, the single most important gas is carbon dioxide which accounts for about 63% of the change in the intensity of the Earth's greenhouse effect as measured in 2005 (Foster et al., 2007). The contributions of the other gases are 18% for methane, 10% for chlorofluorocarbons, and 6% for nitrous oxide. Ozone's contribution to the enhancement of greenhouse effect is still yet to be quantified.
In summary, the greenhouse effect causes the atmosphere to trap more heat energy at the Earth's surface and within the atmosphere by absorbing and re-emitting longwave energy. Of the longwave energy emitted back to space, 90% is intercepted and absorbed by greenhouse gases. Without the greenhouse effect the Earth's average global temperature would be -18° Celsius, rather than the present 15° Celsius. In the last few centuries, the activities of humans have directly or indirectly caused the concentration of the major greenhouse gases to increase. Scientists predict that this increase may enhance the greenhouse effect making the planet warmer. Some experts estimate that the Earth's average global temperature has already increased by 0.3 to 0.6° Celsius, since the beginning of this century, because of this enhancement. Predictions of future climates indicate that by the middle of the next century the Earth's global temperature may be 1 to 3° Celsius higher than today.
Further Reading
- PhysicalGeography.net
- Forster, P., V. Ramaswamy, P. Artaxo, T. Berntsen, R. Betts, D.W. Fahey, J. Haywood, J. Lean, D.C. Lowe, G. Myhre, J. Nganga, R. Prinn, G. Raga, M. Schulz and R. Van Dorland. 2007. Changes in Atmospheric Constituents and in Radiative Forcing. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.). Cambridge University Press, Cambridge, United Kingdom.
Citation
Pidwirny, M. (2012). Greenhouse effect. Retrieved from http://www.eoearth.org/view/article/153146
Q
Greenhouse gas
Published: May 9, 2010, 5:02 pm
Updated: September 22, 2012, 11:56 am
Author: Dave Reay
Author: C Michael Hogan
Methane clathrate deep ocean deposit. Source: Wikimedia Commons
A greenhouse gas is one of several gases that can absorb and emit longwave (infrared) radiation in a planetary atmosphere. This phenomenon is often termed the greenhouse effect. Of the sunlight that falls on the Earth's surface, approximately 40% of that energy is reradiated upward into the atmosphere in the form of longwave radiation. Approximately 75% of that upward radiated longwave energy is absorbed by water vapor, carbon dioxide, methane and other greenhouse gases. Since this absorption process is molecular in nature, the subsequent re-radiation of energy by these gases is multidirectional. As a result, about 50% of the longwave emission is reradiated back toward the Earth where it is once again turned into heat energy. Through this process, greenhouse gases contribute to the amount of heat energy released at the Earth's surface and in the lower atmosphere.
Since the beginning of Industrial Revolution, concentrations of carbon dioxide, methane, and nitrous oxide have all risen dramatically because of human activities. Fossil fuel combustion, land-use change, increasingly intensive agriculture, and an expanding global human population are the primary causes for these increases. Other greenhouse gases found in our planet's atmosphere include water vapor, ozone, sulfur hexafluoride and chlorofluorocarbons.
Carbon Dioxide
Before 1700, levels of carbon dioxide were about 280 ppm (parts per million). Concentrations of carbon dioxide in the atmosphere are now about 390 ppm (Figure 1). This increase in carbon dioxide in the atmosphere is mainly due to activities associated with the Industrial Revolution. Emissions from the combustion of fossil fuels account for about 65% of the carbon dioxide added to the atmosphere. The remaining 35% is derived from deforestation and the conversion of prairie, woodland, and forested ecosystems primarily into less productive agricultural systems. Natural ecosystems can store 20 to 100 times more carbon dioxide per unit area than agricultural systems. Both deforestation and natural land-use change reduce the amount of standing plant mass or biomass found on the Earth’s surface. This reduction causes a net export of carbon stored in biomass into the atmosphere through decomposition and burning.
Figure 1. The following graph illustrates the rise in atmospheric carbon dioxide from 1744 to 2006. Note that the increase in carbon dioxide's concentration in the atmosphere is exponential in nature. An extrapolation into the immediate future would suggest continued annual increases. (Image Copyright: Michael Pidwirny, Data Source: Neftel, A., H. Friedli, E. Moore, H. Lotscher, H. Oeschger, U. Siegenthaler, and B. Stauffer. 1994. Historical carbon dioxide record from the Siple Station ice core. pp. 11-14. In T.A. Boden, D.P. Kaiser, R.J. Sepanski, and F.W. Stoss (eds.) Trends'93: A Compendium of Data on Global Change. ORNL/CDIAC-65. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, Oak Ridge, Tenn. USA and C.D. Keeling and T.P. Whorf. 2001. Carbon Dioxide Research Group, Scripps Institution of Oceanography, University of California, La Jolla, California 92093-0444, USA.).
Fossil Fuel Combustion
Fossil fuel combustion currently contributes about 8.7 gigatonnes of carbon as carbon dioxide to the atmosphere each year. Coal combustion for electricity generation represents the primary source (Figure 2), with oil and gas combustion also being significant contributors.
Figure 2. The Lakeview coal-fired power plant in Mississauga, Ontario, Canada. (Source: Wikimedia Commons, Photographer Hmvh1. This image is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license).
Deforestation Emissions
Deforestation includes tree removal, charcoal production, slash-and-burn practices and forest degradation. In total, these activities contribute approximately 25% of the carbon added to the atmosphere due to human activities, largely as carbon dioxide (Figure 3). Deforestation and land-use change can have a double impact on greenhouse gas fluxes: carbon is released when forests are burned or logged, and the land-based 'sink' of carbon dioxide (the long term uptake and storage of carbon by plants and soils) is reduced when forest is replaced by cropland or rangeland. The majority of carbon dioxide emissions due to deforestation arise from activities in Africa, Asia and South America according to UN FAO sources. It is worth noting that the terrestrial carbon sink - primarily the forests and soils - currently absorbs around 1 billion tonnes of carbon each year from the atmosphere.
Figure 3. Deforestation in Brazil for the purpose of expanding rangeland for livestock..
Source: Antonio Cruz, da Abr. licensed under the Creative Commons Attribution 2.5 Brazil
Carbon Dioxide Sinks
Terrestrial ecosystems emit approximately 119 billion tonnes of carbon each year via the process of respiration and absorb approximately 120 billion tonnes of carbon each year via photosynthesis - a net sink of 1 billion tonnes of carbon. The oceans emit approximately 88 billion tonnes of carbon each year and absorb about 90 billion tonnes of carbon each year - a net sink of about 2 billion tonnes of carbon. Our planet's oceans and terrestrial ecosystems represent net sinks for carbon dioxide, together absorbing approximately 3 billion tonnes of carbon more from the atmosphere each year than they emit. Since the Industrial Revolution these sinks have absorbed about 40% of the carbon dioxide emissions released by human activities.
The response of these land and ocean carbon sinks to climate change in the 21st century remains a key area of uncertainty. Elevated temperatures, changes in rainfall patterns, and acidification of the oceans may serve to reduce the size of the land and ocean sinks - further increasing the concentration of carbon dioxide in the atmosphere.
Methane
Since 1750, atmospheric concentrations of the greenhouse gas methane have increased more than 150% (Figure 4). The primary sources of the man-made methane added to the atmosphere are rice cultivation, ruminant livestock, landfill out-gassing, oil and gas extraction, and coal mining. Key natural sources include wetlands, termites and geological sources such as the thawing of methane clathrates.
Figure 4. The following graph illustrates the rise in atmospheric methane from 1008 to 2001. Note that the increase in methane's concentration in the atmosphere is exponential in nature. An extrapolation into the immediate future would suggest continued annual increases. (Image Copyright: Michael Pidwirny, Data Source: D.M. Etheridge, L.P. Steele, R.J. Francey, and R.L. Langenfelds. 2002. Historical CH4 Records Since About 1000 A.D. From Ice Core Data. In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., USA and Steele, L. P., P. B. Krummel and R. L. Langenfelds. 2002. Atmospheric CH4 concentrations from sites in the CSIRO Atmospheric Research GASLAB air sampling network (October 2002 version). In Trends: A Compendium of Data on Global Change, Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, TN, USA.).
Worldwide the countries responsible for generating significant amounts of methane include China, India, Brazil, Mexico and Russia. These same nations are also projected to still be the greatest generators of methane in the year 2050. The USA and combined European Union countries provide lesser emissions, and the trends in those two advanced regions are flat to down.
Rice Cultivation
Rice cultivation presently accounts for about 20% of worldwide methane emissions, including both natural and human-made sources. Anaerobic conditions associated with rice paddy flooding results in the formation of methane gas. An accurate estimate of how much methane is being produced from rice paddies has been difficult to determine. More than 60% of all rice paddies are found in India and China where scientific data concerning emission rates are hard to obtain. Nevertheless, scientists believe that the contribution of rice paddies is large because this type of crop production has more than doubled since 1950. Much of the recent expansion of rice paddy methane emissions is attributed to the need to feed an expanding human population by increasing crop yields through the cultivation of more land (Figure 5). 
Figure 5. Rice paddy terraces in Sapa, Vietnam. Source: A.J. Oswald/Wikimedia Commons
Ruminant Livestock Emissions
Ruminant grazing is another important source of methane emissions (Figure 6). Grazing animals release methane to the environment as a result of herbaceous digestion. For example, one cow typically produces approximately 150 grams of methane per day. In the USA, the 2010 standing herd of bovines amounted to 106 million animals. These methane emissions are further magnified by the millions of sheep and goats kept worldwide for human use. Some researchers believe the addition of methane from livestock has more than quadrupled over the last century.
Figure 6. Intensive cattle production is a source of significant methane. Image Source: Agricultural Research Service, United States Department of Agriculture
Landfills
Landfills are the second biggest source of methane in the United States. Methane is created in landfills when organic waste decomposes anaerobically (without oxygen). The amount of methane produced depends on factors like the type of waste, moisture content of the waste, and the design and management practices at the landfill. Some landfills reduce methane emissions by burning this gas to produce electrical energy which is sold to utility companies.
Fossil Fuel Extraction
The process of extracting of natural gas, petroleum, and coal from the lithosphere is a significant source of methane emissions (called fugitive emissions) into the atmosphere (Figure 7). Methane emissions also occur during the processing, storage, and distribution of these fossil fuels. Fossil fuel use because of human activities is the fourth largest source of methane emissions in the United States.
Figure 8. Strip coal mining operation in the United States. The mining of coal releases significant quantities of methane to the atmosphere. (Image Source: Wikimedia Commons, Photographer Stephen Codrington. This image is licensed under the Creative Commons Attribution 2.5 Generic license).
Methane Clathrates
Frozen methane clathrate deposits found at the bottom of seabeds and in deep permafrost is a natural source of potential greenhouse gases that may have a significant effect on our planet's climate. Recent scientific studies have found that significant amounts of methane may have been recently released into the atmosphere from methane clathrate deposits found in the Arctic. Research has identified that the release of this methane into the atmosphere may be occurring because of global warming. Further, NASA scientist James Hansen has suggested that methane clathrate emissions may continue to grow because a warmer planet leads to a positive feedback situation (Figure 8).
Figure 8. The future warming of methane clathrate deposits may release methane to the atmosphere creating more global warming. This positive feedback process with feed additional methane release because of the increase in temperature, This cycle could repeat itself many times. Image Source: Michael Pidwirny.
Nitrous Oxide
The average concentration of nitrous oxide in the atmosphere is now increasing at a rate of 0.2 to 0.3% per year (Figure 9). The role of nitrous oxide in the enhancement of the greenhouse effect is smaller than the other greenhouse gases already discussed, but still represents about 6% of climate forcing though human-induced greenhouse gas emissions. Sources for the increase of nitrous oxide in the atmosphere include land-use conversion, fossil fuel combustion, biomass burning, and soil fertilization. Most of the nitrous oxide added to the atmosphere each year due to human activities comes from agricultural soils, where nitrogen-rich fertilizer and manure is converted to nitrous oxide by soil bacteria. Nitrous oxide is also released into the atmosphere when fossil fuels and biomass are burned. 
Figure 9. The following graph illustrates the rise in atmospheric nitrous oxide from 1978 to 2010. An extrapolation into the immediate future would suggest continued annual increases. (Image Copyright: Michael Pidwirny, Data Source: National Oceanic and Atmospheric Administration's (NOAA) Climate Monitoring and Diagnostics Laboratory, http://www.esrl.noaa.gov/gmd/hats/combined/N2O.html).
Chlorofluorocarbons and 'F-gases'
'F-gases' are man-made gases that included chlorofluoracarbons (CFCs), hydrofluorocarbons (HFCs) and sulphur hexafluoride (SF6). They are used as refrigerants, propellants and in electronics manufacture, but are highly persistent in the Earth's atmosphere. They are typically thousands of times more potent as greenhouse gases than carbon dioxide. While reductions in the use of CFCs have been underway in Western Nations for over twenty years, these chemicals are still used in some developing countries. The Montreal Protocol, the international agreement that phases out ozone-depleting substances, requires the end of chlorodifluoromethane production by 2020 in developed countries and 2030 in developing countries. CFCs have been gradually phased out in most nations and replaced by hydrofluorocarbons (HFCs) which avoid ozone depletion problems, but are still very potent greenhouse gases. The Kyoto Protocol aims to reduce emissions of these HFCs by tighter controls and the use of new alternatives such as using butane or propane as the coolant in refrigerators rather than HFCs.
Climate Forcing Effects
In climate science, the relative climate-forcing strength of different greenhouse gases is described relative to that of carbon dioxide. Methane is much more effective at absorbing infrared radiation (heat) and is thus a more powerful greenhouse gas. Yet its lifetime in the atmosphere is only about 10 years, compared to between 30 and 1000 years for a molecule of carbon dioxide. As such, the climate-forcing strength of a kilogram of methane on a 100 year time-horizon – its Global Warming Potential (GWP) – is 25. That is, every kilogram of methane in the atmosphere has the equivalent global warming potential of 25 kilograms of carbon dioxide. The GWP of nitrous oxide is 298.
Our impact on the global climate since the Industrial Revolution has been difficult to interpret. While emissions of greenhouse gases, like carbon dioxide and methane have had a net warming effect, emissions of sulphate aerosols have had a net cooling effect. The net effect is warmer global temperatures, but the complex interaction of these positive and negative influences on the Earth's climate system make predicting future effects difficult.
The problem is exacerbated by our poor level of understanding of exactly how some factors, like land surface albedo (the reflectivity of the land) and cloud cover, operate and interact with changes in global temperature. Another very important greenhouse gas is water vapor and, though human activities are not directly responsible for changes in its concentration in the atmosphere, an indirect increase through elevated surface and lower atmosphere (troposphere) temperatures may lead to an signifcant positive feedback process - making global temperatures even warmer.
The Future
While many developed nations have had carbon emission reduction programs underway for several years, often as part of the United Nations Framework Convention on Climate Change and its 'Kyoto Protocol', their combined emissions have continued to increase. In the coming decades, growth in carbon emissions is likely to be dominated by emissions from developing and transition economies like China and India.
From a technological standpoint, the most straightforward methods of greenhouse gas mitigation are through increased energy efficiency, in production and/or use. Carbon Capture and Storage technologies have been touted as a way to continue fossil fuel based energy generation while reducing emissions of carbon dioxide to the atmosphere. On methane emissions reduction, there is promising research in ruminant feeds, which is leading to per capita cutbacks in animal methane output. In the case of rice farming, changes in land management and crop varieties also hold significant potential.
References
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- Holmes, A. and D. Duff. 1993. Holmes Principles of Physical Geology. Fourth Edition. Routledge, Taylor & Francis Group Ltd., Oxford.
- NOAA. 2010. Emissions of Potent Greenhouse Gas Increase Despite Reduction Efforts U.S. Dept. of Commerce, Washington DC.
- Peake, S. and J. Smith. Climate Change: From Science to Sustainability. Second Edition. Oxford University Press, Oxford.
- Pittock, A.B. 2009. Climate Change: The Science, Impacts and Solutions. Second Edition. CSIRO Publishing, Collingwood, Australia.
- Ruddiman, W.F. 2008. Earth's Climate: Past and Future. Second Edition. W.H. Freeman and Company, New York.
- Schmidt, G. 2004. Methane: A Scientific Journey from Obscurity to Climate Super-Stardom. NASA Goddard Space Center.
- Shakhova, N., I. Semiletov, A. Salyuk, D. Kosmach, and N. Bel’cheva (2007), Methane release on the Arctic East Siberian shelf, Geophysical Research Abstracts, 9, 01071.
- Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (Eds.). 2007. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, 2007. Cambridge University Press, Cambridge, United Kingdom.
- Takahashi, J. and B.A. Young (Editors). 2002. Greenhouse Gases and Animal Agriculture. Proceedings of the 1st International Conference on Greenhouse Gases and Animal Agriculture, Obihiro, Japan, 7-11 November, 2001. Elsevier Sciences, Amsterdam, The Netherlands.
Citation
Reay, D., & Hogan, C. (2012). Greenhouse gas. Retrieved from http://www.eoearth.org/view/article/153147
- See more at: http://www.eoearth.org/view/article/153147/#sthash.UkE2OoDf.dpuf
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Principle 2d
Carbon Cycling
click the image to enlarge the graphic
1. The first involves the sediments at the bottom of the oceans: Carbon dioxide dissolves into cold ocean water at high latitudes. That CO2 is then carried to the deep ocean by sinking currents where it stays in sediments for hundreds of years. Thus deep ocean currents pump carbon from the atmosphere into the sea for storage.
2. Plants also reduce carbon in the atmosphere through photosynthesis: They use energy from the sun to combine CO2 from the atmosphere and water from the soil to make carbon-rich carbohydrates like glucose.Thus plants extract CO2 from the atmosphere and accumulate it in their tissues. Conversely, cutting down trees, or deforestation, and the burning of fossil fuels increases CO2 in the atmosphere.
3. Some carbon is transformed into calcium carbonate (limestone), the largest carbon reservoir on Earth. Read more…
Carbon Cycling
This diagram of the fast carbon cycle shows the movement of carbon between land, atmosphere, and oceans. Yellow numbers are natural fluxes, and red are human contributions in gigatons of carbon per year. White numbers indicate stored carbon. All numbers are in gigatons. (Diagram adapted from U.S. DOE, Biological and Environmental Research Information System.)
The level of greenhouse gases in the atmosphere is controlled by cycles. Those cycles move carbon between the ocean, land, different life forms, and the atmosphere. Here are three examples:
1. The first involves the sediments at the bottom of the oceans: Carbon dioxide dissolves into cold ocean water at high latitudes. That CO2 is then carried to the deep ocean by sinking currents where it stays in sediments for hundreds of years. Thus deep ocean currents pump carbon from the atmosphere into the sea for storage.
2. Plants also reduce carbon in the atmosphere through photosynthesis: They use energy from the sun to combine CO2 from the atmosphere and water from the soil to make carbon-rich carbohydrates like glucose.Thus plants extract CO2 from the atmosphere and accumulate it in their tissues. Conversely, cutting down trees, or deforestation, and the burning of fossil fuels increases CO2 in the atmosphere.
3. Some carbon is transformed into calcium carbonate (limestone), the largest carbon reservoir on Earth.
These are three examples of cycles that directly or indirectly relate affect our climate. Of these, the carbon cycle has been involved in long-term climatic change in geological history. Carbon cycling involves many carbon-containing compounds, including short-term organic, long-term organic, and inorganic compounds.
Biological processes involving the carbon cycle have relatively short time spans influenced by photosynthesis and diurnal (day-night) and annual cycles. On a longer time span, carbon dioxide is moved from the atmosphere and the ocean and into terrestrial deposits through biologic and geologic processes.
Carbon cycle
Published: May 31, 2010, 7:46 pm
Updated: May 7, 2012, 11:29 am
Author: Michael Pidwirny
Figure 1: Carbon cycle. (Source: PhysicalGeography.net)
All life is based on the element carbon. Carbon is the major chemical constituent of most organic matter, from fossil fuels to the complex molecules (DNA and RNA) that control genetic reproduction in organisms. Yet by weight, carbon is not one of the most abundant elements within the Earth's crust. In fact, the lithosphere is only 0.032% carbon by weight. In comparison, oxygen and silicon respectively make up 45.2% and 29.4% of the Earth's surface rocks.
Carbon is stored on our planet in the following major sinks (Figure 1 and Table 1): (a) as organic molecules in living and dead organisms found in the biosphere; (b) as the gas carbon dioxide in the atmosphere; (c) as organic matter in soils; (d) in the lithosphere as fossil fuels and sedimentary rock deposits such as limestone, dolomite and chalk; and (e) in the oceans as dissolved atmospheric carbon dioxide and as calcium carbonate shells in marine organisms.
Photosynthesis and respiration
Ecosystems gain most of their carbon dioxide from the atmosphere. A number of autotrophic organisms have specialized mechanisms that allow for absorption of this gas into their cells. With the addition of water and energy from solar radiation, these organisms use photosynthesis to chemically convert the carbon dioxide to carbon-based sugar molecules. Each year, photosynthesis by terrestrial plants moves about 110 petagrams (1 petagram = 1015 grams = 1012 kilograms = 1 billion metric tons; so 110 petagrams = 110 billion metric tons) of carbon from the atmosphere to the biota. These molecules can then be chemically modified by these organisms through the metabolic addition of other elements to produce more complex compounds like proteins, cellulose, and amino acids. Some of the organic matter produced in plants is passed down to heterotrophic animals through consumption.
Figure 1: Carbon cycle. (Source: PhysicalGeography.net)
Carbon is released from ecosystems as carbon dioxide gas by the process of respiration. Respiration takes place in both plants and animals and involves the breakdown of carbon-based organic molecules into carbon dioxide gas and some other compound byproducts. The detritus food chain contains a number of organisms whose primary ecological role is the decomposition of organic matter into its abiotic components. Each year, respiration by organisms other than detrivores returns to the atmosphere almost half (50 petagrams or 50 billion metric tons) of the carbon dioxide that is absorbed by photosynthesis. Another portion of the carbon that flows from the atmosphere to the biota becomes part of the detritus food chain. Partially decomposed organic matter becomes part of the soil carbon storage pool. Eventually, the organic material in the soil is decomposed to its constituents, water and carbon dioxide, which return to the atmosphere. This flow of carbon is known as decay and accounts for about 60 petagrams (60 billion metric tons). Together with respiration, these flows account for most but not all of the carbon removed from the atmosphere by photosynthesis.
Carbon in the oceans
| Table 1: Estimated major stores of carbon on the Earth. | Sink | Amount in Billions of Metric Tons | |
| Atmosphere | 578 (as of 1700) - 766 (as of 1999) | ||
| Soil Organic Matter | 1500 to 1600 | ||
| Ocean | 38,000 to 40,000 | ||
| Marine Sediments and Sedimentary Rocks | 66,000,000 to 100,000,000 | ||
| Terrestrial Plants | 540 to 610 | ||
| Fossil Fuel Deposits | 4000 | ||
CO2 + H2O ? H2CO3
This reaction has a forward and reverse rate. These two reqctions achieve a chemical equilibrium in which they both occur at equal rates, thus mainting a relatively stable ratio of CO2 to H2CO3. Another reaction that is important in controlling the acidity (i.e. pH levels) of the oceans is the release of hydrogen ions and bicarbonate:
H2CO3 ? H+ + HCO3−
This reaction buffers seawater against large changes in pH.
Certain forms of sea life biologically fix bicarbonate with calcium (Ca+2) to produce calcium carbonate (CaCO3). This substance is used to produce shells and other hard body parts by organisms such as coral, clams, oysters, some protozoa, and some algae. When these organisms die, their shells and body parts sink to the ocean floor where they accumulate as carbonate-rich deposits. After long periods of time, these deposits are physically and chemically altered into sedimentary rocks. Ocean deposits are by far the biggest sink of carbon on the planet (Table 1).
Carbon in the lithosphere
Carbon is stored in the lithosphere in both inorganic and organic forms. Inorganic deposits of carbon in the lithosphere include fossil fuels like coal, oil, and natural gas, oil shale, and carbonate-based sedimentary deposits like limestone. Organic forms of carbon in the lithosphere include litter, organic matter, and humic substances found in soils. Some carbon dioxide is released from the interior of the lithosphere by volcanoes. Carbon dioxide released by volcanoes enters the lower lithosphere when carbon-rich sediments and sedimentary rocks are subducted and partially melted beneath tectonic boundary zones.
Human role in the carbon cycle
Until recently, the flow of carbon stored in fossil fuels to the atmosphere was minuscule—nearly zero. The fossil fuel storage represented a “dead-end” for the carbon cycle. The Industrial Revolution increased the use of coal, oil, and natural gas. Burning fossil fuels completes the process of break-down back to carbon dioxide and water. In 2000, humans burned about 5.1 billion short tons (4.6 billion metric tons) of coal, 28.1 billion barrels of oil, and 89 trillion cubic feet of natural gas, which caused about 6.5 petagrams (6.5 billion metric tons) of carbon to flow from the fossil fuel storage pool to the atmosphere.
The combustion of fossil fuels is not the only flow in the carbon cycle affected by economic activity. Prior to the expansion of human civilization, the amount of carbon stored in biota changed very slowly from year to year because the amount taken up through photosynthesis was nearly equal to the amount emitted through respiration and decomposition. But human activity has disturbed the biotic storage pool. Over the last several hundred years, humans have reduced the area covered by forests, a process known as deforestation. By reducing the number of trees through burning and/or chopping them down and allowing them to decay, deforestation reduces the amount of carbon stored in the biota. This carbon flows to the atmosphere. In the 1990’s, deforestation and other changes in land use caused 1-2 petagrams (1-2 billion metric tons) of carbon to flow from the biota to the atmosphere annually.
The other important set of flows moves carbon from the atmosphere to the ocean and from the ocean to the atmosphere. For a long time, these two flows were approximately equal. This balance was created and maintained by the spontaneous flow of carbon from the storage of high concentration to the storage with the lower concentration. These movements created an equilibrium between the amount of carbon in the atmosphere and ocean.
This equilibrium has been disrupted by the combustion of fossil fuels and deforestation. These two flows add carbon to the atmosphere, which causes the concentration of carbon to increase in the atmosphere relative to the ocean. The increased atmospheric concentration of carbon causes carbon to flow spontaneously from the atmosphere to the ocean. The size of this flow is limited by a negative feedback loop, termed the Revelle Factor, which slows the flow of carbon from the atmosphere to the ocean relative to the flow of carbon to the atmosphere. As carbon dioxide dissolves in the ocean, it reduces the ocean’s pH (makes it more acidic). The lower pH slows the rate at which carbon dioxide dissolves in the ocean. Currently, the flow of carbon from the atmosphere to the ocean is about 2 petagrams (2 billion metric tons) greater than the flow of carbon from the ocean to the atmosphere.
The “missing” carbon
Despite the scientific certainty that the global carbon cycle is governed by the law of conservation, scientists are not able to “balance” the storages and flows. That is, summing the best estimates for the flows of carbon to and from the atmosphere indicates that there is less carbon in the atmosphere than expected. During the 1990’s, the atmosphere was missing about 3 petagrams (3 billion metric tons) of carbon per year. This missing carbon is associated with an unknown carbon sink.
Figure 2. Spatial distribution of estimated increase in net primary production from 1982 to 1999. (Source: Climate-Driven Increases in Global Terrestrial Net Primary Production from 1982 to 1999. Ramakrishna R. Nemani, Charles D. Keeling, Hirofumi Hashimoto, William M. Jolly, Stephen C. Piper, Compton J. Tucker, Ranga B. Myneni, and Steven W. Running (6 June 2003). Science 300 (5625), 1560.)
The unknown carbon sink is either an unknown mechanism that removes carbon from the atmosphere and/or a known mechanism that removes carbon faster than estimated by scientists. There are several hypotheses concerning the unknown carbon sink. Many are based on negative feedback loops that include the atmospheric concentration of carbon dioxide. One hypothesis is that the increasing concentration of carbon dioxide in the atmosphere increases net primary production, and this speeds the rate at which carbon is pulled from the atmosphere. Experiments indicate that plants grow faster at higher concentration of carbon dioxide, but it is not clear whether this increase is significant in the real world. If the growth of plants is not limited by the availability of carbon in the atmosphere, increasing its concentration will not increase growth. On the other hand, the mechanism may be boosted by human activities that increase the availability of nitrogen to plants.
Another hypothesis for the unknown carbon sink focuses on climate. The increasing concentration of carbon dioxide in the atmosphere is partially responsible for the global increase in temperature. As the world gets warmer, this could enhance plant growth, which would speed the rate at which plants remove carbon from the atmosphere via net primary production (Figure 2). Recent research suggests that climatic changes have enhanced plant growth in northern mid-latitudes and high latitudes. Global changes in climate have eased several critical climatic constraints to plant growth, such that net primary production increased 6% (3.4 petagrams of carbon over 18 years) globally. The largest increase was in tropical ecosystems. Amazon rain forests accounted for 42% of the global increase in net primary production, owing mainly to decreased cloud cover and the resulting increase in solar radiation.
Alternatively, the increase in temperature could accelerate the rate of decay. Decay frees up nutrients that were previously “tied up” in the organic material. If these nutrients are limiting in a Leibigian sense, the increased supply could accelerate net primary production and therefore speed the rate at which carbon dioxide is removed from the atmosphere. But if the nutrients were not limiting, accelerated rates of decay would increase the flow of carbon dioxide to the atmosphere.
Recent trends in atmospheric carbon dioxide
Even though scientists cannot balance the global carbon cycle, it is clear that the amount of carbon entering the atmosphere is greater than the amount of carbon leaving the atmosphere. Over the last 30 years, the amount of carbon stored in the atmosphere has increased, which we see as a significant increase in the atmospheric concentration of carbon dioxide (CO2) (Figure 3). The so-called Mauna Loa curve shows that between 1959 and 2008, the concentration of carbon in the atmosphere increased from about 317 parts per million (ppm) to 380 ppm. This increase is worrisome because the amount of carbon dioxide in the atmosphere influences the amount of heat retained, which may alter global climate. Notice too that the increase in is not steady. Within each year, the concentration of carbon dioxide rises and falls. This intrannual cycle allows us to watch the planet “breathe.”
Figure 3. The Mauna Loa atmospheric carbon dioxide curve: 1958-2008. (Image Source: Wikimedia, Artist Robert A. Rohde. Data Source : Keeling, C.D. and T.P. Whorf. 2005. Atmospheric CO2 records from sites in the SIO air sampling network. In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A. This image is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license.).
The Mauna Loa atmospheric CO2 measurements constitute the longest continuous record of atmospheric CO2 concentrations available in the world. The Mauna Loa site is considered one of the most favorable locations for measuring undisturbed air because possible local influences of vegetation or human activities on atmospheric CO2 concentrations are minimal and any influences from volcanic vents may be excluded from the records. The methods and equipment used to obtain these measurements have remained essentially unchanged during the monitoring program that has been running for more than 50 years.
Further Reading
- Houghton, Richard. Understanding the Global Carbon Cycle. The Woods Hole Research Center.
- Nemani, Ramakrishna R., Keeling, Charles D., Hashimoto, Hirofumi, Jolly, William M., Piper, Stephen C., Tucker, Compton J., Myneni, Ranga B.,and Running, Steven W. 2003. Climate-Driven Increases in Global Terrestrial Net Primary Production from 1982 to 1999. Science, 300(5625):1560.
- PhysicalGeography.net
Pidwirny, M. (2012). Carbon cycle. Retrieved from http://www.eoearth.org/view/article/150923
- See more at: http://www.eoearth.org/view/article/150923/#sthash.kf7GCTpl.dpuf
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Deforestation in Amazonia
Published: March 30, 2007, 3:24 pm
Updated: April 5, 2013, 5:29 pm
Author: Philip M. Fearnside
Massive defoestation in Mato Grosso, Brazil. Source: Pedro Biondi
Introduction
Transamazon Highway. (Source: Philip M. Fearnside)
Tropical forests in Amazonia are being cleared rapidly, representing an important worldwide element of land-use and land-cover change. While some processes are common to forests throughout the world, others are not. Amazonian clearing is dominated by large cattle ranchers, with an increasing role being played by soybeans. Small farmers and estate crops such as oil palm have less relative importance here than elsewhere. Deforestation in Brazilian Amazonia has a significant contribution from “ulterior” motives such as land speculation, money laundering and tax evasion. Infrastructure projects, especially highway construction and improvement, represent key governmental decisions unleashing chains of activity that escape from government control. Deforestation sacrifices environmental services such as maintenance of biodiversity, water cycling and carbon stocks. The substantial impact of this deforestation on loss of environmental services has so far not entered into decision-making on infrastructure projects, making strengthening of the environmental assessment and licensing system a high priority for containing future loss of forest.
History
Deforestation has been a feature of Amazonian landscape since long before the arrival of Europeans in the 1500s. Indeed, no forest in the region can be considered “virgin” in the sense of being unaffected by past human activities. Prior to decimation of their populations by disease and violence from the Europeans, indigenous peoples maintained extensive areas of agriculture and they enriched the surrounding forest with useful species such as Brazil nuts. These human influences would be merged with forest regrowth during the lapse of three centuries before non-tribal populations reached levels sufficient to begin exerting significant pressure on the forest. Contrary to the claims of some, this history of past human disturbance in no way diminishes the rationale for conserving Amazonian forests today. Likewise, the exuberant forests that now stand on formerly cleared areas do not justify the myth of a future recovery-that forests being cleared today may one day regrow to their former stature. In practice, secondary forests are recleared for cattle pasture or other uses long before they regain the biomass and diversity of “primary” forests.
Fig. 1. Map describing major ecoregions of Brazil, indicating ten sampling localities of An. darlingi. Ecoregions are: north Amazon River (NAR); south Amazon River (SAR); Cerrado (CER); coastal Atlantic Forest (CAF); interior Atlantic Forest (IAF). These ecoregions are from 10 states: AM: Amazonas, AP: Amapá, ES: Espírito Santo, GO: Goiás, MT: Mato Grosso, PA: Pará, PR:Paraná, RJ: Rio de Janeiro, SP: São Paulo, TO: Tocantins. http://dx.doi.org/10.1016/j.meegid.2012.04.002
In Brazil, deforestation over the course of several centuries destroyed the Atlantic forest of the south-central part of the country (note: the names of Brazil’s regions treat Rio de Janeiro as the “center” of the country). The pace of clearing was especially dramatic in the case of state of Paraná, where the forest was almost completely cleared in less than 30 years in the middle of the 20th century. At the beginning of this period prominent citizens frequently made statements to the effect that Paraná’s forests were so vast that human efforts would “never” put more than a dent in them. The similarity of these statements to those sometimes made today with reference to the Amazon forest is evident, as is the irony of their baselessness.
Deforestation in Amazonia has proceeded with a succession of different forces in different periods. The Amazon rubber boom lasted from the invention of the pneumatic tire in the 1880s to the beginning of commercial rubber production from plantations in Southeast Asia in 1914. During this period “agricultural colonies” such as those in the 35,000-square-kilometer (km2) Zona Bragantina near Belém, in the state of Pará, supplied the rapidly growing urban centers, and, to a certain extent, the population engaged full-time in exploitation of the natural rubber trees in the Amazonian interior. Much of the agricultural land was abandoned to secondary forest when the rubber boom collapsed. More recent clearing surges occurred with the opening of the Belém-Brasília Highway in the late 1950s, and especially the Transamazon Highway in 1970 (the event often taken as the beginning of the “modern” period of Amazonian clearing). The Transamazon Highway was settled by small farmers, many of whom were brought from other parts of Brazil by the federal government and settled in official colonization projects. This much-publicized initiative was soon overshadowed in terms of its impact on deforestation by the large cattle ranchers who received generous tax incentives and subsidized financing from the government though the Superintendency for the Development of Amazonia (SUDAM). Large and medium-sized ranchers continue to account for the bulk of clearing in Brazilian Amazonia. The relative role of small versus large actors is an important difference between different locations in Brazilian Amazonia, between different historical periods, and between Brazil and other countries.
Current rates and causes
Arc of Deforestation in the region of Terra do Meio. (Source: Philip M. Fearnside)
Global generalizations about the role of “poverty” in tropical deforestation generally do not apply to Brazil, where most clearing is done by the rich. Cattle ranching is the use put to the great majority of land cleared, either immediately upon clearing in the case of large ranchers, or after a harvest or two of an annual crop in the case of small farmers. Although the government incentives programs of the 1970s and 1980s have been either discontinued or have diminished in importance, government infrastructure investment and agricultural credit continue to encourage clearing. Logging has a key role in serving as a source of funds for landholders to pay for deforestation. Logging also provides initial access roads, which can then be used and improved by those who later deforest the areas. Unlike the clear cutting that is done for timber harvesting in temperate and boreal forests, logging in Amazonia is always selective because only a few species have commercial value. The disturbed forest that remains after logging is much more susceptible to fire than are unlogged forests.
Deforestation in Amazonia is often not “rational” from the normal financial perspective of paying an attractive return on money invested, at least when only legal money flows are considered. In practice, deforesters make their decisions based on the combined total of all benefit streams, including those that may be undeclared and/or illegal. Investment in Amazonian land can serve as a means of laundering money from illegal sources such as drug trafficking, corruption, sale of stolen goods and income from legitimate activities that is undeclared to tax authorities. For money from these sources the sale of any beef or other products produced in the Amazonian landholdings represents legal income, whereas the investment needed to produce it is highly variable and easily underdeclared to tax authorities.
Burning and deforestation of the Amazon forest to make grazing lands. Source: (NASA LBA-ECO Project)
“Ulterior” motives for clearing also include potential returns from land speculation. The value of land in Amazonia has generally climbed upward and invariably shoots to much higher levels where a road is built or improved. Buying land or claims to land at low prices and reselling it later at much higher prices can give greater returns to a landholder than do the ranching and agriculture that are undertaken during his tenure. Clearing a portion of the land is the only practical way to maintain claim to the area and avoid it being invaded by landless peasants, taken over by another large operator, or confiscated by the government for agrarian reform. Prior to the 1994 “Plano Real” economic reform, Brazil’s rate of inflation was much higher than it is today and land speculation represented a more powerful force, as was shown by the drop by over 50% in the deforestation rate in 1996 and 1997 in parallel with falling land values resulting from the removal of inflation as a driving force. Today, although there is no longer a need to invest funds in real estate as an escape from inflation, profits can still be made by individual landholders when infrastructure projects lead to increasing land values.
A state of lawlessness prevails in substantial areas in Amazonia, leading to distinctive “leaps” in the deforestation frontier. Most notorious is the “Terra do Meio”, or “Middle Lands” to the west of the Xingu River encompassing the Iriri River basin. This area, the size of Switzerland, has effectively been outside of the control of the Brazilian government and is the realm of drug traffickers, illegal loggers and grileiros, or large land thieves who appropriate land through fraudulent (and sometimes violent) means. Declaration of a series of reserves in the area in 2005, following the assassination of Sister Dorothy Stang, is a hopeful sign that the lawless condition is subject to change. The activities of grileiros continue in other locations, most recently increasing in the southern part of the state of Amazonas.
A new and increasing force driving deforestation is export commodities such as soybeans and beef. Soybeans have taken over much of the cerrado (central Brazilian savanna) and are advancing in some rainforest areas such as Santarém, Pará. Soybeans have a large indirect force on deforestation by providing economic justification for highway construction projects that spur forest loss through cattle ranching, logging and land speculation. Beef export has traditionally not been a force behind deforestation in Brazil (in sharp contrast to the “hamburger connection” of Central America) because the presence of foot-and-mouth disease made major markets in Europe, Japan and North America unwilling to import beef in frozen form. Since 1996 states in Brazil have successively been certified as free of foot-and-mouth disease, starting in the extreme south of the country and now including three of the nine Amazonian states. The impact of beef export on deforestation already affects all of Amazonia, even though most of the area is still uncertified and cannot export beef directly. Instead, beef produced outside of Amazonia, for example in the state of São Paulo, can be exported while the people in São Paulo eat beef raised in Pará.
Over 80% of both the cumulative clearing and the current clearing activity is concentrated in the “arc of deforestation,” which is a band along the eastern and southern edges of the forest. Deforestation advances from this band towards the center of the region. However, in addition to the expansion from existing clearings in the arc of deforestation, smaller clearings that appear far from the existing frontier have an importance that is much greater than their small area would suggest. These new clearings can serve as the seeds for much greater clearing activity in the future in the remaining blocks of undisturbed forest. Decisions on building highways that open these areas to migration and to investment are critical in speeding the deforestation process.
Future paths
Intact Amazon forest near Manaus. (Source: Philip M. Fearnside)
The future path of deforestation depends on human decisions. It is not foreordained that the Amazon forest will be destroyed, although this is obviously the endpoint if present trends continue unchanged. Various modeling efforts have projected clearing patterns in Amazonia and agree that vast areas would be cleared if trends continue and planned infrastruture projects are built. Attempts to model what might happen under hypothetical “governance” scenarios are less convincing, since they rely on simple assumptions of restraint and obedience to environmental regulations that are at variance with observed behavior to date. Nevertheless, the potential to change deforestation behavior is real, both through creation of protected areas and through command and control measures to repress illegal clearing. An important historical example is the deforestation licensing and control program that was carried out by the state government in Mato Grosso over the 1999-2001 period, where clearing patterns indicated that the program had a real effect on deforestation rates. This is important as a demonstration that deforestation can be controlled if government authorities are serious about doing so. The example is historical, as the election of Brazil’s largest soybean entrepreneur as state governor in 2002 put an end to the program in practice.
So far the principal measures that have been used to limit deforestation are creation of reserves and repression by fining those who clear without required authorizations. These are the measures that agencies such as the Brazilian Institute for the Environment and Renewable Natural Resources (IBAMA) are empowered to implement. However, the better-funded government agencies such as the Ministry of Transportation continue to plan and build roads and other infrastructure projects without regard for impact on deforestation. While the environmental licensing process for infrastructure projects may lead to compensatory actions, such as creation of reserves and funding of programs for monitoring and enforcement of regulations, the licensing has on many occasions shown itself to be incapable of stopping damaging projects and either diverting development efforts to less-damaging alternatives to achieve the same objectives or forcing a rethinking of the wisdom of the objectives themselves. Environmental impact studies (EIS) have only been required in Brazil since 1986 and the system is still subject to continual challenges and (often successful) attempts to build infrastructure with either no EIS (e.g., the proposed BR-319 Highway) or with an inadequate EIS that is effectively replaced with a package of parallel activities that escape from the legal requirement of serving as prerequisites for the infrastructure (e.g., the proposed BR-163 Highway). Building and improving highways is one of the principal ways that government decisions affect the deforestation process; the consequences of these decisions are much more far reaching than are the effects of any compensatory programs such as environmental education, promotion of agroforestry and the like. One of the most basic measures needed is strengthening the environmental impact assessment and licensing system such that it serves its intended role of informing major decisions before they are made, rather than as a formality to legalize decisions that have already been made.
Indigenous lands and various categories of parks and reserves represent a primary defense against deforestation.
Indigenous peoples, whose officially recognized lands represent approximately 20% of Brazilian Amazonia, actively defend their territories against invasion. An essential complement to this is the general understanding that invasion of indigenous land will not be rewarded by a land title or by any sort of compensation. In many places in the arc of deforestation the only forest that remains standing is what is in indigenous areas.
Since the mid 1990s tremendous progress has been made in “demarcating” indigenous areas, that is, marking the limits of these areas on the ground (as opposed to merely drawing them on a map). At the same time, large areas have been protected in newly created conservation units, both by federal and state governments. These include an increasing number of “sustainable use” reserves, although a number of new reserves have also been created in the “integral protection” category. Conservation units now total roughly 10% of Brazilian Amazonia. Decreeing a reserve, even if only on paper, can have a significant effect in discouraging both small squatters and large grileiros from clearing forest with the expectation of eventually receiving legal title to their claims. In the longer term “paper parks” are not enough—the reserves must be adequately guarded. Expansion of the reserve network must be done quickly because the opportunity to create reserves is often lost once deforestation advances into an area. Reserve creation is a critical step in guiding the development of Amazonia towards a future that maintains substantial areas of tropical forest.
Impacts
Amazonian deforestation causes serious impacts that, if counted in decision making, would often be seen to outweigh the benefits derived from clearing. Loss of biodiversity is one such impact, which implies both loss of the value of the direct uses to which the species lost might be put by humans and the loss of existence values that are independent of such direct uses. Deforestation impacts are magnified by the pattern of clearing that leaves the remaining forest divided into fragments, which then degrade both biodiversity and carbon stocks.
BR-319 Highway. (Source: Philip M. Fearnside)
Deforestation also affects water cycling, because conversion of forest to cattle pasture results in the water running off into the rivers and flowing directly to the ocean without being recycled through the trees. A significant part of the rainfall in Amazonia, especially in the dry season, depends on water that has been recycled through the trees of the forest. This water is critical to preventing droughts from exceeding the forest’s tolerance for water stress, leading to death of trees and degradation of the forest through fire and further drought. Water from Amazonia is also critical to maintaining rainfall in the heavily populated regions in south-central Brazil, such as São Paulo, and in neighboring countries such as Argentina.
Global warming receives a substantial input of greenhouse gases from Amazonian deforestation, although the majority of the gases released by humanity as a whole come from burning fossil fuels such as petroleum and coal rather than from deforestation. However, over three-fourths of Brazil’s contribution to this global problem is the result of Amazonian deforestation. Half of the dry weight of the trees is carbon, and when forest is cut this carbon is released to the atmosphere either as carbon dioxide or as methane, both from burning and from decomposition of wood that fails to burn. The fact that most deforestation is for cattle pastures that do little either for the national economy or for providing employment to the population offers an opportunity to slow deforestation as part of a program for mitigating global warming. The value of the damage done by greenhouse-gas emissions from deforestation far exceeds the value of the timber, beef and other products that are sold as a result of the clearing.
Alternatives
Discussion of “alternatives to deforestation” often focuses on the extraction of non-timber forest products such as rubber and Brazil nuts, sustainable forest management for timber, and increasing the production and sustainability of land uses in already deforested areas, for example by encouraging agroforestry. These “alternatives” all have their places, but they also have limitations and are often misrepresented with respect to their role in slowing deforestation. The economic logic that activities expand when they prove to be profitable applies to those undertaken in deforested areas, and what may be intended as an “alternative” can, if it proves highly successful, advance into the forest and have the opposite effect on deforestation. Proposals for intensified pasture production and for extensive production of biofuels are subject to these reservations. The same applies to annual crops: the notion that farmers and ranchers who reap greater per-hectare yields will be satisfied with their harvests and refrain from further deforestation is unrealistic as a basis for programs aimed at reducing deforestation. Unfortunately, people do not stop clearing when their stomachs are full, but instead use their increased wealth to expand their clearings.
Uses of standing forest such as sustainable (i.e., low intensity) harvesting of both non-timber and timber products often produce low financial returns. This is to be expected, but the rationale for promoting and subsidizing these uses lies in their role in maintaining environmental services, not in their efficiency as commodity sources. These activities are valuable as transitional mechanisms for maintaining traditional populations who can serve as forest guardians. The same activities can also serve as parts of future mechanisms whereby environmental services of standing forest become the primary means of generating income to support the rural population, and the basis of the economy is shifted from its present reliance on forest destruction. Among the environmental services of the forest, carbon storage is the closest to becoming the basis of substantial financial flows through international negotiations, but the equally valuable services of maintaining biodiversity and water cycling can eventually be expected to gain similar status.
Further Reading
- Publications on Human Carrying Capacity, Agroecosystems, Deforestation, and Development Planning in Brazilian Amazonia, National Institute for Research in the Amazon (INPA).
- Expanding Deforestation in Mato Grosso, Brazil, NASA Earth Observatory
- Deforestation in the Amazon, Rhett A Butler, Mongabay.com.
Citation
Fearnside, P. (2013). Deforestation in Amazonia. Retrieved from http://www.eoearth.org/view/article/151675
Q
Principle 2e
Aerosols
Aerosols are simply particles that are airborne. They have a complex effect on the Earth's energy balance: (1) They can cause cooling, by reflecting incoming sunlight back out to space. (2) They can cause warming, by absorbing and releasing heat energy in the atmosphere.
Small solid and liquid particles can be carried into the atmosphere through a variety of natural and man-made processes, including volcanic eruptions, sea spray, forest fires, and emissions generated through human activities (things like exhaust from your car or a power plant). Read more…
Aerosols
Aerosols are simply particles that are airborne. They have a complex effect on the Earth's energy balance: (1) They can cause cooling, by reflecting incoming sunlight back out to space. (2) They can cause warming, by absorbing and releasing heat energy in the atmosphere. 
Small solid and liquid particles can be carried into the atmosphere through a variety of natural and man-made processes, including volcanic eruptions, sea spray, forest fires, and emissions generated through human activities (things like exhaust from your car or a power plant).
While the role of aerosols in the climate system has been known since the late 1800s, their complex interactions on climate are still being studied. Some may have a cooling effect in the short term but a warming effect in the long term. Black carbon, an important aerosol, is now considered to be the second largest contributor to global warming after carbon dioxide. However, since black carbon remains in the atmosphere for only days to weeks, reducing it before it enters the atmosphere may prove to be an efficient way to slow near-term climate change. (In contrast, CO2 stays in the atmosphere for hundreds of years.) However, when black carbon falls on snow or ice, it reduces the albedo of those surfaces. Albedo, meaning "whiteness", relates to the ability of a surface to reflect solar energy. Therefore, black carbon contributes to a positive feedback loop: as albedo is reduced, more radiation is absorbed by the surface, which leads to an increased rate of melting of snow and ice, which leads to even more reduced albedo. Burning of forests and savannahs and combustion of fossil fuels account for about 80% of black carbon, commonly known as soot, in the atmosphere.
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When viewed from space, a number of patterns emerge from Earth’s aerosols—some driven by nature and others by man.
Nature generates broad swaths of particles—detectable by satellites—over both water and land. The strong winds of the “roaring forties” latitudes, for example, create a heavy band of airborne salt north of Antarctica. A thinner and more evenly dispersed veil of aerosols—primarily salt from whitecaps and sulfates from microalgae—usually covers most of the world’s oceans. Over land, massive plumes of dust blow above deserts.
Meanwhile, the eastern portion of the United States and urban areas in Europe are hotspots for the production of human-made aerosols. Plumes of industrial aerosols — typically sulfates from coal power plants and black and organic carbon from vehicle traffic — rise from cities such as New York, Pittsburgh, London, and Berlin.
The western portion of the United States is comparatively clear, though some areas experience aerosol loads that rival the worst conditions in the East. Industrial aerosols, dust, and wildfire smoke frequently pollute the air in the Los Angeles Basin. Agriculture can produce heavy loads of soil dust, especially in California’s San Joaquin and Imperial valleys, and the largest localized source of dust in the western U.S. is Owens Dry Lake, a river bed that was drained to provide water for LA. Likewise, the port of Houston has some of the most aerosol-laden air in the world.
Aerosols and Incoming Sunlight (Direct Effects)
Source: http://earthobservatory.nasa.gov/Features/Aerosols/page3.php
The Sun provides the energy that drives Earth’s climate, but not all of the energy that reaches the top of the atmosphere finds its way to the surface. That’s because aerosols—and clouds seeded by them—reflect about a quarter of the Sun’s energy back to space.
Aerosols play an important role in Earth’s climate. Most aerosols are brighter than land or ocean, and cool the Earth by reflecting sunlight back to space. (NASA astronaut photograph.)
Different aerosols scatter or absorb sunlight to varying degrees, depending on their physical properties. Climatologists describe these scattering and absorbing properties as the “direct effect” of aerosols on Earth’s radiation field. However, since aerosols comprise such a broad collection of particles with different properties, the overall effect is anything but simple.
Although most aerosols reflect sunlight, some also absorb it. An aerosol’s effect on light depends primarily on the composition and color of the particles. Broadly speaking, bright-colored or translucent particles tend to reflect radiation in all directions and back towards space. Darker aerosols can absorb significant amounts of light.
Pure sulfates and nitrates reflect nearly all radiation they encounter, cooling the atmosphere. Black carbon, in contrast, absorbs radiation readily, warming the atmosphere but also shading the surface. Organic carbon, sometimes called brown carbon or organic matter, has a warming influence on the atmosphere depending on the brightness of the underlying ground. Dust impacts radiation to varying degrees, depending on the composition of the minerals that comprise the dust grains, and whether they are coated with black or brown carbon. Salt particles tend to reflect all the sunlight they encounter.
Black carbon aerosols, similar to the soot in a chimney, absorb sunlight rather than reflecting it. This warms the layer of the atmosphere carrying the black carbon, but also shades and cools the surface below. (Maps adapted from Chung, 2005.)
Aerosols can have a major impact on climate when they scatter light. In 1991, the eruption of Mount Pinatubo in the Philippines ejected more than 20 million tons of sulfur dioxide—a gas that reacts with other substances to produce sulfate aerosol—as high as 60 kilometers (37 miles) above the surface, creating particles in the stratosphere. Those bright particles remained above the clouds and didn’t get washed from the sky by rain; they settled only after several years.
Climatologists predicted global temperatures would drop as a result of that global sulfate infusion. They were right: Following the eruption, global temperatures abruptly dipped by about a half-degree (0.6°C) for about two years. And Pinatubo isn’t a unique event. Large, temperature-altering eruptions occur about once per decade.
Large volcanic eruptions may lift sulfate aerosols into the stratosphere, which usually cools the global climate for the following year or two. (Graph by Robert Simmon, based on aerosol data from GISS and temperature data from the UAE CRU.)
In addition to scattering or absorbing radiation, aerosols can alter the reflectivity, or albedo, of the planet. Bright surfaces reflect radiation and cool the climate, whereas darker surfaces absorb radiation and produce a warming effect. White sheets of sea ice, for example, reflect a great deal of radiation, whereas darker surfaces, such as the ocean, tend to absorb solar radiation and have a net warming effect.
Aerosols, particularly black carbon, can alter reflectivity by depositing a layer of dark residue on ice and other bright surfaces. In the Arctic especially, aerosols from wildfires and industrial pollution are likely hastening the melting of ice.
Dark aerosols dramatically change the reflectivity of the Earth’s surface when they land on snow. Black ash covered the summit of New Zealand’s Mount Ruapehu after an eruption in 2007, but was soon covered by fresh snow. Long-term accumulation of black carbon aerosols in the Arctic and Himalaya is leading to increased melting of snow. (Photograph ©2007, New Zealand GeoNet.)
Scientists believe the cooling from sulfates and other reflective aerosols overwhelms the warming effect of black carbon and other absorbing aerosols over the planet. Models estimate that aerosols have had a cooling effect that has counteracted about half of the warming caused by the build-up of greenhouse gases since the 1880s. However, unlike many greenhouse gases, aerosols are not distributed evenly around the planet, so their impacts are most strongly felt on a regional scale.
Despite considerable advances in recent decades, estimating the direct climate impacts of aerosols remains an immature science. Of the 25 climate models considered by the Fourth Intergovernmental Panel on Climate Change (IPCC), only a handful considered the direct effects of aerosol types other than sulfates.
Q
Principle 2f
Feedback Loops
A big change in any one component of the climate system can influence the entire Earth system. Positive feedback loops can amplify these effects and trigger abrupt changes in the climate system—changes more rapid and on a larger scale than projected by current climate models.
Feedback loops are found in many natural processes. For example: The relationship between snow and ice cover and greenhouse gases trapped under snow and ice generates a positive feedback loop that releases additional greenhouse gases as the planet warms (see the diagram at right). Read more…
Feedback Loops
The woolly mammoth was one of the large mammals that became extinct in North America at the onset of the Younger Dryas approx. 13,000 years ago.
A big change in any one component of the climate system can influence the entire Earth system. Positive feedback loops can amplify these effects and trigger abrupt changes in the climate system—changes more rapid and on a larger scale than projected by current climate models.
Feedback loops are found in many natural processes. For example: The relationship between snow and ice cover and greenhouse gases trapped under snow and ice generates a positive feedback loop that releases additional greenhouse gases as the planet warms
Abrupt climate change triggered by feedback loops in the climate system have occurred many times in Earth’s history. One of the most well-known examples of abrupt change is referred to as the Younger Dryas event or "Big Freeze", and it occurred 14,500 years ago as the Earth's climate began to shift from a cold glacial world to a warmer interglacial state. Partway through this transition, temperatures in the Northern Hemisphere suddenly returned to near glacial conditions for about 1,300 years.
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What is causing Arctic sea ice decline?
Readers sometimes ask us, “What are the reasons behind Arctic sea ice decline?” In summer months, ice extent has declined by more than 30 percent since the start of satellite observations in 1979. But is climate change really the culprit, or could other factors be contributing?
Scientists have long suspected that the decline in summer sea ice was too strong to be caused by natural variations, such as weather patterns that cause fast changes in ice extent. Climate model simulations have shown that sea ice will decline as the Arctic gets warmer. But Arctic ice has declined faster than models predicted, raising the possibility that massive sea ice loss was caused at least in part by natural variations in weather.
This month, researchers at the Max Planck Institute for Meteorology in Germany released a new study examining all the possible drivers for the observed sea ice retreat. Study lead Dirk Notz said, “There has always been the chance that we simply observed a freak encounter of unusual natural variability with very low ice cover.”
Looking for a smoking gun
Notz said, “The whole study was based on ruling out one possible cause after the other.” The team looked at each possible cause of ice loss, using statistical analyses to determine whether a particular cause could explain the ice decline. The scientists first considered natural variability, or the effect of short-term and seasonal weather conditions and winds. While variable winds and weather clearly play a role in how much ice melts each summer, they found that the amount of variability was far too low to explain the intensity of the decline.
The researchers then looked at the possibility that ice loss was leading to more ice loss, in a vicious cycle known as a positive feedback loop. As ice declines, the increased areas of open water absorb more heat, which can then melt more ice. This is one reason that researchers are concerned about declining sea ice. However, the new study concluded that such a feedback cannot explain the amount of ice loss that has already occurred. Notz said, “After each year with an extreme ice loss, the ice cover always recovered somewhat. Self acceleration is not a major player in the Arctic at the moment.”
Notz and colleagues then looked at other possible drivers for ice decline, ranging from solar radiation and cosmic rays, to volcanic eruptions, wind patterns, and oceanic heat transport. For all of these potential causes, their analysis showed that none of these were correlated with ice extent.
“In the end, only the increase in CO2 remained on our list of possible drivers,” Notz said, “We find a clear, physically plausible correlation of increasing CO2 and decreasing sea-ice cover.” While other research has previously shown a connection between sea ice decline and global warming, most of those studies focused on climate models. The new study provides an independent confirmation that sea ice is in fact declining because of human-caused climate change.
The Arctic Ocean has lost more than 30 percent of its summer ice cover in the last thirty years. Scientists have long thought that climate change is to blame, but a new study provides more evidence for that idea. Credit: Patrick Kelley, U.S. Coast Guard. High Resolution Image
Q
Principle 2g
Local Relevance
Burning on the Prairies of the Great Plains
What does it mean for the carbon cycle?
Adapted From: https://asr.science.energy.gov/science/research-highlights/RNDcz/viewThe deep drought in the United States that fueled wildfires and damaged crops in 2012 continued well into 2013.
However, long before the droughts and fires wreaked havoc, a team of scientists from the U.S. Department of Energy’s (DOE) Lawrence Berkeley National Laboratory (LBNL) and the U.S. Department of Agriculture’s (USDA) Grazing Lands Research Laboratories were already collaborating—to ask the question, “How do these events impact carbon cycling on prairies, an ecosystem that once dominated the Great Plains?”
In a recent paper, team leader Marc L. Fischer (LBNL), discusses how they may have found the beginnings of an answer in grass—or more accurately, the lack of it.
For two years, 2005 and 2006, rainfall on the U.S. Great Plains was lower than average. The DOE/USDA team used that time to capture the impacts of dry years and fires on prairies. In a controlled manner, they burned a pasture in Oklahoma that contained tall grass species native to the region. During the two years, the research team measured growth of grass species and the rate of exchange of carbon, water, and heat on the burned patch. The Atmospheric Radiation Measurement (ARM) Climate Research Facility, which maintains a large climate research facility in Oklahoma, provided the samples and instrumentation necessary for this team effort.
The scientists also made the same measurements on an adjacent unburned pasture that was similar in all respects to the one they burned. The results of the study appeared last December in the journal Agricultural and Forest Meteorology.
Fischer and his team found that under normal to somewhat dry conditions, like those of 2005, grass production during growing season—which follows the dry season when fires typically break out—captured most of the carbon that the patch had lost during burning. Grass production captures and stores atmospheric carbon, whereas decay and burning releases carbon back into the atmosphere; the latter produces soot and gases that release carbon faster than the slower decay process.
The capture and release of carbon is an important component of the carbon cycle—the continuous and life-sustaining process of recycling carbon between the earth, ocean, soil, organisms, and atmosphere. In 2006, however, which had a very dry growing season, Fischer and his team found that grass production was stunted both in the burned as well unburned fields: so much so, that both fields exchanged very little carbon. The researchers concluded that it is the dry conditions that control the rate of carbon exchange rate on the prairies by reducing uptake.
Today prairie grasslands cover more than 20 percent of the Earth’s surface and hold more than 10 percent of the Earth’s total carbon. To evaluate how drawn-out (at times for decades) extreme droughts and accompanying fires impact the carbon cycle on grasslands, the research team have undertaken experiments to monitor carbon, water, and heat exchange rates in crop and prairie fields in the Southern Great Plains.
Principle 2h
Misconceptions about this Principle
The Misconception
Isn’t it true that the planet cooled mid-century during a period of post World War II industrialization when CO2 emissions were rising?
The misconception goes something like this: If CO2 really is responsible for global warming, then why don’t we see a consistent rise in temperatures during the 20th century since CO2 levels were rising throughout the century and especially during the post WWII period? Instead we see a cooling period from the 1940s to the 1970s.
The Science
CO2 was increasing during the period following WWII, but so were sulphate aresols, which had a pronounced cooling effect because they reflect incoming solar energy back into space and lead to cooling.
The science says: Although temperatures increased overall during the 20th century, three distinct periods can be observed. Global warming occurred both at the beginning and at the end of the 20th century, but a cooling trend is seen from about 1940 to 1975. As a result, changes in 20th century trends offer a good framework through which to understand climate change and the role of numerous factors in determining the climate at any one time. Read more…
Source: http://www.skepticalscience.com/global-cooling-mid-20th-century.htm
The Science
CO2 was increasing during the period following WWII, but so were sulphate aresols, which had a pronounced cooling effect because they reflect incoming solar energy back into space and lead to cooling.
The science says: Although temperatures increased overall during the 20th century, three distinct periods can be observed. Global warming occurred both at the beginning and at the end of the 20th century, but a cooling trend is seen from about 1940 to 1975. As a result, changes in 20th century trends offer a good framework through which to understand climate change and the role of numerous factors in determining the climate at any one time.
Early and late 20th century warming has been explained primarily by increasing solar activity and increasing CO2 concentrations, respectively, with other factors contributing in both periods. So what caused the cooling period that interrupted the overall trend in the middle of the century? The answer seems to lie in solar dimming, a cooling phenomenon caused by airborne pollutants.
The main culprit is likely to have been an increase in sulphate aerosols, which reflect incoming solar energy back into space and lead to cooling. This increase was the result of two sets of events.
Industrial activities picked up following the Second World War. This, in the absence of pollution control measures, led to a rise in aerosols in the lower atmosphere (the troposphere).
A number of volcanic eruptions released large amounts of aerosols in the upper atmosphere (the stratosphere). Combined, these events led to aerosols overwhelming the warming trend at a time when solar activity showed little variation, leading to the observed cooling. Furthermore, it is possible to draw similar conclusions by looking at the daily temperature cycle. Because sunlight affects the maximum day-time temperature, aerosols should have a noticeable cooling impact on it. Minimum night-time temperatures, on the other hand, are more affected by greenhouse gases and therefore should not be affected by aerosols. Were these differences observed? The answer is yes: maximum day-time temperatures fell during this period but minimum night-time temperatures carried on rising.
The introduction of pollution control measures reduced the emission of sulphate aerosols. Gradually the cumulative effect of increasing greenhouse gases started to dominate in the 1970s and warming resumed.
As a final point, it should be noted that in 1945, the way in which sea temperatures were measured changed, leading to a substantial drop in apparent temperatures. Once the data are corrected, it is expected that the cooling trend in the middle of the century will be less pronounced.
Principle 2
Check your Knowledge of this Principle
To pass this knowledge check you will need to have read the main paragraphs for each topic of the principle.