The presence of small amounts of heat-trapping greenhouse gases in the atmosphere warms Earth's surface, resulting in a planet that sustains liquid water and life. Jump to Greenhouse Gases Make the Earth Habitable
Culture, Climate Science & Education
Click the Double Arrows () to Explore this Principle
Principle Three: Life Affects Climate
The Cultural Value is Relatedness
Episode Three: Grizzly Bears and Wilderness
Episode 3: Grizzly Bears and Wilderness
Transcript with Description of Visuals
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Soft instrumental music: |
Flying above a long, finger-shaped lake that lies at the bottom of a timbered canyon. A snow covered peak lies at the head of the canyon. |
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Voice Over continues: |
A man and a girl, Alyssa Pretty On Top, hike in the canyon on a trail that runs along the base of a cliff. The camera view changes to an aerial shot of the two walking, then to a view of their feet as they hike up the trail. |
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Ryan Adams: |
The two stop at a rocky outcrop overlooking the lake. At the head of the canyon is a large mountain, McDonald Peak. Ryan talks as they look out across the wooded canyon. |
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Alyssa's voice over continues: |
Alyssa looking through binoculars, scanning an area across the canyon, looking for bears. Scene changes to a mother grizzly bear with two small cubs. All three are watching something in the distance. The cubs stand on their hind feet and watch intensely. |
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As I've learned today, changes in our climate affect all living things, from grizzly bears to small berries and nuts. |
Scene changes to Alyssa and Rylee, her cousin, walking with their grandfather along the shore of the McDonald Lake, the large lake in the bottom of the canyon. |
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Alyssa and Rylee's grandfather: |
Alyssa and Rylee sit on a large rock on the lake shore, listening to their grandfather, who is leaning against a boulder. |
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Alyssa's voice over continues: |
Scene changes to large adult grizzly bear, that appears to be standing, its head filling the camera frame. |
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As we face climate change, there is so much we can and need to do to help our relatives. The future of human beings is tied to the future of bears and all the other animals and plants. |
Scene changes back to Alyssa, Rylee, and their grandfather at the lake shore, as the camera flies over and past them and up the canyon above the lake. |
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Soft Instrumental Music |
The following credits in white text over a black background: |
Principle 3
What You Need to Know About Principle 3: Life Affects Climate, Climate Affects Life
Plants and animals, even microorganisms influence climate. They have also been influencing the Earth’s climate for billions of years, ever since microbes began changing the atmosphere.
This principle is about the relationship between the biosphere and the climate system, including the annual changes in the amount of carbon dioxide (CO2) in the atmosphere. Annually, the amount of CO2 increases in the spring and summer months and decreases in the winter because during the growing season plants use photosynthesis to draw CO2 from the atmosphere and release oxygen. Click the tabs below to learn more about how climate and living things interact.
The biosphere is the global sum of all ecosystems on Earth. It is the zone of life.
- Individual Plant and Animal Species Require Specific Climatic Conditions to Survive
Individual plants and animals survive within specific ranges of temperature, precipitation, humidity, and sunlight. Organisms exposed to climate conditions outside their normal range must adapt or migrate, or they will perish. Jump to Plant and Animal Species
- Greenhouse Gases Make the Earth Habitable
- Changes in the Climate can Affect Ecosystems
Changes in climate conditions can affect the health and function of ecosystems and the survival of entire species.The distribution patterns of fossils show evidence of gradual as well as abrupt extinctions related to climate change in the past. Jump to Changes in the Climate can Affect Ecosystems
- Over Most of the Last 10,000 Years, Earth’s Climate has been Unusually Stable
A range of natural records shows that the last 10,000 years have been an unusually stable period in Earth's climate history. Modern human societies developed during this time. The agricultural, economic, and transportation systems we rely upon are vulnerable if climate changes significantly. Jump to Earth’s Climate has been Unusually Stable
- Life on Earth is a Major Driver of the Global Carbon Cycle
Life — including microbes, plants, and animals and humans — is a major driver of the global carbon cycle and can influence global climate by modifying the chemical makeup of the atmosphere. The geologic record shows that life has significantly altered the atmosphere during Earth's history. Jump to Life on Earth is a Major Driver of the Carbon Cycle
Principle 3a
Individual Plant and Animal Species Require Specific Climatic Conditions to Survive
Individual organisms survive within specific ranges of temperature, precipitation, humidity, and sunlight.
Organisms exposed to climate conditions outside their normal range must adapt or migrate, or they will perish.
Scientists have a special term to describe changes in an individual organism over the course of its lifetime: phenotypic plasticity. That's a mouthful, but the idea is straightforward. An organism's phenotype is simply its set of features, and to be plastic means to be moldable or changeable — so phenotypic plasticity just means that an organism's features can be molded, or influenced to some degree, by its environment.
A grizzly bear changing its diet from berries to apples or corn during bad berry years is an example of phenotypic plasticity because it did not require a genetic change. Even though the bear did not evolve with corn or apples, it can change its diet to take advantage of them.
This is different from genetic adaptation, which involves a genetic change or mutation that becomes dominant through natural selection. An example would be a rabbit that grows white fur in the winter and brown fur in the summer, a genetic trait that was selected for because it improved the species’ survivability. Read More…
Individual Plant and Animal Species Require Specific Climatic Conditions to Survive
Individual organisms survive within specific ranges of temperature, precipitation, humidity, and sunlight.
Organisms exposed to climate conditions outside their normal range must adapt or migrate, or they will perish.
Scientists have a special term to describe changes in an individual organism over the course of its lifetime: phenotypic plasticity. That's a mouthful, but the idea is straightforward. An organism's phenotype is simply its set of features, and to be plastic means to be moldable or changeable — so phenotypic plasticity just means that an organism's features can be molded, or influenced to some degree, by its environment.
A grizzly bear changing its diet from berries to apples or corn during bad berry years is an example of phenotypic plasticity because it did not require a genetic change. Even though the bear did not evolve with corn or apples, it can change its diet to take advantage of them.
This is different from genetic adaptation, which involves a genetic change or mutation that becomes dominant through natural selection. An example would be a rabbit that grows white fur in the winter and brown fur in the summer, a genetic trait that was selected for because it improved the species’ survivability.
Some species that are capable of phenotypic plasticity will be able to survive the changes climate change brings to their habitats. Others will not and will simply go extinct. Some of the best available science indicates that if increases in greenhouse gases stay on pace, species will go extinct at an ever-increasing rate, according to a 2015 study published in Science. In the worst-case scenario, global warming will contribute to wiping out one of every six species.
The concept of phenotypic plasticity encompasses all sorts of changes to individual organisms, including developmental changes (e.g., an organism reaching a larger body size if it gets good nutrition as a juvenile, but reaching a smaller size with poor nutrition), behavioral changes (e.g., a polar bear eating goose eggs instead of seals, if seals become hard to catch and eggs are plentiful), and physical changes (e.g., a rabbit that grows white fur in the winter and brown fur in the summer). Phenotypic plasticity includes any sort of change to an individual that isn't caused by changes in its genes.
Recent research makes it clear that we can expect global warming to impact species in all of these ways. Some organisms will be able to cope because they have the right sort of phenotypic plasticity.
So, for example, birds that are able to change their ranges and live where the environment suits them are likely to benefit from being phenotypically plastic. As the climate warms, they will be able to "track" the shifting habitats that are best for their survival.
Other species, like the Canadian squirrel, may evolve as the Earth continues to warm. But, of course, the biggest and most worrying news is the many species that may fall into neither of these categories, lacking both the plasticity that would allow them to better cope with climate change and the genetic variation that would allow them to evolve in response to climate change.
Polar bears may be in this slowly sinking boat as are an estimated one of every six species on Earth. The long generation times of polar bears and their relatively small population sizes make evolutionary adaptation unlikely. And it's unclear if they are phenotypically plastic enough to successfully make a living in a new, warmer world. Unless we can mitigate the impact of climate change, many of the species we love and depend on may soon face extinction.
Adapted from: Coping with climate change.
UC Berkeley. May 2009
Climate Impacts on Ecosystems
Source: http://www.epa.gov/climatechange/impacts-adaptation/ecosystems.html
Climate is an important environmental influence on ecosystems. Climate changes and the impacts of climate change affect ecosystems in a variety of ways. For instance, warming could force species to migrate to higher latitudes or higher elevations where temperatures are more conducive to their survival. Similarly, as sea level rises, saltwater intrusion into a freshwater system may force some key species to relocate or die, thus removing predators or prey that were critical in the existing food chain.
Climate change not only affects ecosystems and species directly, it also interacts with other human stressors such as development. Although some stressors cause only minor impacts when acting alone, their cumulative impact may lead to dramatic ecological changes. [1] For instance, climate change may exacerbate the stress that land development places on fragile coastal areas. Additionally, recently logged forested areas may become vulnerable to erosion if climate change leads to increases in heavy rain storms.
Changes in the Timing of Seasonal Life-Cycle Events
For many species, the climate where they live or spend part of the year influences key stages of their annual life cycle, such as migration, blooming, and mating. As the climate has warmed in recent decades, the timing of these events has changed in some parts of the country. Some examples are:
Changes like these can lead to mismatches in the timing of migration, breeding, and food availability. Growth and survival are reduced when migrants arrive at a location before or after food sources are present. [4]
Range Shifts
As temperatures increase, the habitat ranges of many North American species are moving northward in latitude and upward in elevation. While this means a range expansion for some species, for others it means a range reduction or a movement into less hospitable habitat or increased competition. Some species have nowhere to go because they are already at the northern or upper limit of their habitat.
For example, boreal forests are invading tundra, reducing habitat for the many unique species that depend on the tundra ecosystem, such as caribou, arctic fox, and snowy owl. Other observed changes in the United States include expanding oak-hickory forests, contracting maple-beech forests, and disappearing spruce-fir forests. As rivers and streams warm, warmwater fish are expanding into areas previously inhabited by coldwater species. [5] Coldwater fish, including many highly valued trout species, are losing their habitats. As waters warm, the area of feasible, cooler habitats to which species can migrate is reduced. [5] Range shifts disturb the current state of the ecosystem and can limit opportunities for fishing and hunting.
See the Agriculture and Food Supply Impacts & Adaptation page for information about how habitats of marine species have shifted northward as waters have warmed.
Food Web Disruptions
The impact of climate change on a particular species can ripple through a food web and affect a wide range of other organisms. For example, the figure shows the complex nature of the food web for polar bears. Declines in the duration and extent of sea ice in the Arctic leads to declines in the abundance of ice algae, which thrive in nutrient-rich pockets in the ice. These algae are eaten by zooplankton, which are in turn eaten by Arctic cod, an important food source for many marine mammals, including seals. Seals are eaten by polar bears. Hence, declines in ice algae can contribute to declines in polar bear populations. [4] [5] [6]
Threshold Effects
In some cases, ecosystem change occurs rapidly and irreversibly because a threshold, or "tipping point," is passed.
One area of concern for thresholds is the Prairie Pothole Region in the north-central part of the United States. This ecosystem is a vast area of small, shallow lakes, known as "prairie potholes" or "playa lakes." These wetlands provide essential breeding habitat for most North American waterfowl species. The pothole region has experienced temporary droughts in the past. However, a permanently warmer, drier future may lead to a threshold change—a dramatic drop in the prairie potholes that host waterfowl populations and provide highly valued hunting and wildlife viewing opportunities. [3]
Similarly, when coral reefs become stressed, they expel microorganisms that live within their tissues and are essential to their health. This is known as coral bleaching. As ocean temperatures warm and the acidity of the ocean increases, bleaching and coral die-offs are likely to become more frequent. Chronically stressed coral reefs are less likely to recover.
Pathogens, Parasites, and Disease
Climate change and shifts in ecological conditions could support the spread of pathogens, parasites, and diseases, with potentially serious effects on human health, agriculture, and fisheries. For example, the oyster parasite, Perkinsus marinus, is capable of causing large oyster die-offs. This parasite has extended its range northward from Chesapeake Bay to Maine, a 310-mile expansion tied to above-average winter temperatures. [8] For more information about climate change impacts on agriculture, visit the Agriculture and Food Supply Impacts & Adaptation page. To learn more about climate change impacts on human health, visit the Health Impacts & Adaptation page.
View enlarged image
The Arctic food web is complex. The loss of sea ice can ultimately affect the entire food web, from algae and plankton to fish to mammals. Source: NOAA (2011)
Extinction Risks
Climate change, along with habitat destruction and pollution, is one of the important stressors that can contribute to species extinction. The IPCC estimates that 20-30% of the plant and animal species evaluated so far in climate change studies are at risk of extinction if temperatures reach levels projected to occur by the end of this century. [1] Projected rates of species extinctions are 10 times greater than recently observed global average rates and 10,000 times greater than rates observed in the distant past (as recorded in fossils). [2] Examples of species that are particularly climate sensitive and could be at risk of significant losses include animals that are adapted to mountain environments, such as the pika, animals that are dependent on sea ice habitats, such as ringed seals, and cold-water fish, such as salmon in the Pacific Northwest. [5]
References
1. Fischlin, A., G.F. Midgley, J.T. Price, R. Leemans, B. Gopal, C. Turley, M.D.A. Rounsevell, O.P. Dube, J. Tarazona, A.A. Velichko (2007). Ecosystems, their Properties, Goods, and Services. In: Climate Change 2007: Impacts, Adaptation and Vulnerability . 
Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Parry, M.L., O.F. Canziani, J.P. Palutikof, P.J. van der Linden, and C.E. Hanson (eds.). Cambridge University Press, Cambridge, United Kingdom.
2. Millennium Ecosystem Assessment (2005). Ecosystems and Human Well-Being: Biodiversity Synthesis (PDF). World Resources Institute, Washington, DC, USA.
3. CCSP (2009). Thresholds of Climate Change in Ecosystems . A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. Fagre, D.B., Charles, C.W., Allen, C.D., Birkeland, C., Chapin, F.S. III, Groffman, P.M., Guntenspergen, G.R., Knapp, A.K., McGuire, A.D., Mulholland, P.J., Peters, D.P.C., Roby, D.D., and Sugihara, G. U.S. Geological Survey, Department of the Interior, Washington DC, USA.
4. CCSP (2008). The Effects of Climate Change on Agriculture, Land Resources, Water Resources, and Biodiversity in the United States . A Report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research. Backlund, P., A. Janetos, D. Schimel, J. Hatfield, K. Boote, P. Fay, L. Hahn, C. Izaurralde, B.A. Kimball, T. Mader, J. Morgan, D. Ort, W. Polley, A. Thomson, D. Wolfe, M. Ryan, S. Archer, R. Birdsey, C. Dahm, L. Heath, J. Hicke, D. Hollinger, T. Huxman, G. Okin, R. Oren, J. Randerson, W. Schlesinger, D. Lettenmaier, D. Major, L. Poff, S. Running, L. Hansen, D. Inouye, B.P. Kelly, L Meyerson, B. Peterson, and R. Shaw. U.S. Environmental Protection Agency, Washington, DC, USA.
5. USGCRP (2009). Global Climate Change Impacts in the United States . Karl, T.R., J.M. Melillo, and T.C. Peterson (eds.). United States Global Change Research Program. Cambridge University Press, New York, NY, USA.
6. ACIA (2004). Impacts of a Warming Arctic: Arctic Climate Impact Assessment . Arctic Climate Impact Assessment. Cambridge University Press, Cambridge, United Kingdom.
7. NRC (2008). Understanding and Responding to Climate Change: Highlights of National Academies Reports . National Research Council. The National Academies Press, Washington, DC, USA.
8. NRC (2008). Ecological Impacts of Climate Change . National Research Council. The National Academy Press, Washington, DC, USA.
Q
How a Few Species Are Hacking Climate Change
Animals can be surprisingly adaptable—but can they change quickly enough?
BYLINE
By Emma Marris, for National Geographic
http://news.nationalgeographic.com/news/2014/05/140506-climate-change-adaptation-evolution-coral-science-butterflies/
PUBLISHED MAY 06, 2014
European larger banded snails (Cepaea nemoralis), such as this one in Italy, with light colored shells are becoming more prevalent over time in the Netherlands.
PHOTOGRAPH BY FRANCESCO TOMASINELLI, VISUALS UNLIMITED/CORBIS
As the Earth heats up, animals and plants are not necessarily helpless. They can move to cooler climes; they can stay put and adapt as individuals to their warmer environment, and they can even adapt as a species, by evolving.
The big question is, will they be able to do any of that quickly enough? Most researchers believe that climate change is happening too fast for many species to keep up. (Related: "Rain Forest Plants Race to Outrun Global Warming.")
But in recent weeks, the general gloom has been pierced by two rays of hope: Reports have come in of unexpected adaptive ability in endangered butterflies in California and in corals in the Pacific.
Two isolated reports don't, of course, diminish the gravity of the global threat. But they do highlight how little we still know about nature's ability to cope with climate change.
"Most of the models that ecologists are putting out are assuming that there's no adaptive capacity. And that's silly," says Ary Hoffmann, a geneticist at the University of Melbourne in Australia and the co-author of an influential review of climate change-related evolution. "Organisms are not static."
Nature on the Move
That species are on the move is becoming obvious not just to scientists but also to gardeners and nature-lovers everywhere. Butterflies are living higher up on mountains; trees are moving north in North America and Europe. In North Carolina, residents are still agog at encountering nine-banded armadillos, which have invaded the state from the south.
A 2011 review of data on hundreds of moving species found a median shift to higher altitudes of 36 feet (11 meters) per decade and a median shift to higher latitudes of about 10.5 miles (17 kilometers) per decade.
There's also a clear warming-related trend in the timing of natural events. One study suggests that spring shifted 1.7 days earlier between 1954 and 2007. Insects are emerging earlier; birds are nesting earlier; plants are flowering and leafing out earlier. The latest of such natural events studies, out last month, shows that climate change has stretched out the wildflower bloom season in Colorado by 35 days.
The report last month from a butterfly conference in England was a bit different, however. It concerned the endangered quino checkerspot butterfly (Euphydryas editha quino), well known for being threatened by climate change. Many experts believed the species was doomed unless humans collected the butterflies and moved them north; their path to higher ground seemed to be blocked by the megalopolis of Los Angeles.
But at the conference, according to an account in the Guardian, Camille Parmesan of the Marine Sciences Institute at Plymouth University in the U.K., who has studied the quino checkerspot for years, reported that it had miraculously shifted its range to higher altitudes. Furthermore, it had somehow learned to lay its eggs on a new host plant.
"Every butterfly biologist who knew anything about the quino in the mid-1990s thought it would be extinct by now, including me," Parmesan told the Guardian. (Parmesan confirmed the account for National Geographic, but declined to elaborate until she could publish her own research paper on the subject.)
Resilience in Corals
Another uplifting tale of unexpected resilience appeared in Science on April 24. While surveying the waters of the future National Park of American Samoa off Ofu Island, researcher Peter Craig noticed isolated coral pools that were considerably warmer than the rest. High water temperatures can cause corals to "bleach": They spit out the photosynthesizing algae that live inside them, thereby losing both their color and their means of collecting energy. Yet these particular corals didn't seem to be suffering too much from the heat.
Marine ecologist Stephen Palumbi of Stanford University in California tested the heat tolerance of some of the Acropora hyacinthus corals from unusually hot pools. He plopped them into a container, then cranked up the heat inside to 34 degrees Celsius (93 degrees Fahrenheit) for three hours. Just 20 percent of the individual coral animals spit out their algae, whereas 55 percent of coral from an otherwise similar but much cooler pool spit out their algae during the test.
The more revealing test came next. Palumbi took corals from the cool pool and put them in the hot pool. One year later, he measured their heat tolerance—and found it had greatly improved. The heat stress test caused only 32.5 percent of the transplanted corals to spit out their algae, instead of 55 percent.
Palumbi's experiment helped tease out the two different mechanisms by which organisms can adapt. Individual transplanted corals were able to adapt to the hotter water, without any change in their genes. Biologists call that phenotypic plasticity.
But the transplanted corals were still not as good at taking the heat as corals that were native to the hot pools; 32.5 percent of them bleached during the stress test, compared with just 20 percent of the hot-pool natives. That gap might reflect the operation of another mechanism of adaptation: genetic evolution. Over many generations, natural selection may have changed the genes of corals in the hot pools by allowing the most heat-tolerant ones to survive and produce more offspring.
For the Samoan corals in a warming ocean, the combination of plastic adaptation and genetic evolution could be "the difference between dead and more or less unfazed," Palumbi says. The results suggest to him that previous predictions of extinction for all coral might be a bit too pessimistic.
More generally, such individual stories of adaptive ability suggest that the quality of resilience has been left out of our models and predictions about how the natural world will respond to climate change. "I do think there is more hidden adaptability out there," says Palumbi.
Snails, Salmon, Owls, and Thyme
So far, evidence of adaptability is available for only a few species. Juha Merilä of the University of Helsinki in Finland, who edited a special issue of the journal Evolutionary Applications in January rounding up the evidence for such changes, guesses that there are perhaps 20 studies robustly linking adaptation through phenotypic plasticity to climate change, and another 20 or so clearly linking climate change with genetic evolution. But, he says, it's likely that this is a tiny fraction of the species in which adaptation is occurring.
There are better data on shifts in ranges and the timing of events, thanks in part to citizen science efforts like Project Budburst and the Great Backyard Bird Count. But these studies don't prove whether the shifts are due to plasticity or genes, or even that climate change is the underlying cause—they're just highly suggestive correlations between rising temperatures and the location and behavior of species.
Among the most solid examples of actual evolution in response to climate change is a shift in the proportion of European larger banded snails (Cepaea nemoralis) with light colored shells. Shell color is genetic, and the genes responsible are known. It has been shown that, in a given environment, snails with light colored shells have a lower body temperature than those with dark colored shells. And light colored shells are becoming more prevalent over time in the Netherlands, even in wooded, shady environments where you might expect dark shells to dominate.
A few other studies have caught species actually evolving in response to climate change. Pink salmon in Auke Creek, Alaska, which is heating up .03 degrees Celsius (.054 degrees Fahrenheit) per year, are now migrating out of the creek earlier, and scientists have shown that that change is genetic.
Wild thyme (Thymus vulgaris) in France has evolved in response to fewer extreme cold events since the 1970s, producing more pungent oils to deter herbivores (at the cost of becoming less cold-hardy).
Tawny owls (Strix aluco) can be light gray or brown, depending on the genes they inherit from their parents. As snow cover in Finland has declined since the late 1970s, the light gray owls, best camouflaged during snow, no longer have much of an advantage, and scientists have shown that brown owls are now much more common.
Such studies require patience. "It is really hard to get the evidence because you need long-term studies and it is very hard to make science over these kinds of periods," says Merilä. The snails have been studied for at least 45 years, the owls for 36, and the salmon for 32.
And such studies also leave unresolved how one ought to feel about these subtle transformations. When we see spring springing earlier or snails changing color, should we mourn the changes as sad, human-caused degradation, or embrace them as evidence of plucky nature fighting back? "A bit of both," says Hoffmann. "We have to accept that things will change."
"I think we should feel impressed by the impact that we have, that we can change the course of evolution around us by the way we change the environment," says Menno Schilthuizen, who studies how invertebrates adapt to climate change at the Naturalis Biodiversity Center in Leiden, Netherlands. "Our impact is much further and deeper than we tend to think."
Some Will Die
Researchers on this topic are quick to point out that evolution and individual plasticity won't save all species. Climate change is happening too fast, they say, for some species to survive.
Hypotheses abound on which species are likely to keep up with climate change. Species with short lives, like fruit flies, have more generations in which to evolve, compared with long-lived species that don't begin to breed for decades. And some species, like some conifer trees, simply have more gene variants to work with in their populations.
Conversely, long-lived species with low genetic variability—including many rare mammals—will have less adaptive ability. "In general, you might expect that weedy, short-lived species and ones that are able to disperse widely might be favored," says Steven Franks, who studies how plants adapt to climate change at Fordham University in New York.
There's also a widespread but still poorly tested hypothesis that tropical species may have a harder time evolving than temperate species do. Having evolved in a region with less climate variability over both the years and the millennia, tropical species may harbor a less diverse set of genes related to heat tolerance and similar traits. "The tropics are hot, but they are not particularly variable," Hoffmann says. "It is not like they are being challenged all the time."
Predicting which species will survive on their own can help researchers zero in on which species might benefit most from human help. A key goal of such an intervention would be to bring back genetic diversity to small, isolated populations so that evolution has something to work with. "Where we have a fragmented landscape, we should connect it up again, restore the flow," says Hoffmann. "We are restoring a process, and that process is really powerful."
Where it's not possible to connect fragmented populations with contiguous habitat, "restoring the flow" could mean moving seeds or individuals from population to population. In dire cases, Hoffmann says, conservationists might want to create hybrids of two related species or subspecies, if each one is insufficiently able to adapt on its own. "People think 'genetic pollution!'" he says. "But you could achieve a lot in terms of saving these populations."
Palumbi, meanwhile, thinks the adaptability he found in Samoan corals won't save them as much as provide a grace period; eventually, he says, human-made climate change could outstrip the corals'—and many other species'—ability to adapt.
"That delay of a couple of decades is the good news here," he says. "Let's use the decades to solve the problem." And when he says "the problem," he means the root of the problem: carbon emissions.
Q
Adaptation or plasticity?
Many recent changes in organisms have been chalked up to climate change. Which of those represent adaptation and which represent phenotypic plasticity? Here are a few examples from each category:
Adaptation:
Canadian squirrels have evolved earlier breeding times. Squirrels with genes for earlier breeding were probably favored because this allows them to take advantage of an earlier spring and hoard more pinecones for winter survival.
A North American mosquito species has evolved to wait longer before going dormant for the winter. Mosquitoes with genes that cause them to go dormant later were probably favored because it allows the insects to gather more resources during our new, extra-long summers.
Plasticity:
Some plant species around Walden Pond are flowering as much as three weeks earlier than they did 150 years ago. In these species, flowering is partly triggered by temperature, so climate change is the likely cause of this shift.
Most butterfly species in central California have been taking flight about 24 days sooner in comparison to 30 years ago. When butterfly species mature is closely related to temperature, so climate change is the likely cause of this shift
Alpine plant species in Austria and Switzerland have changed their range and are now found at higher altitudes than they were 100 or so years ago. Many plant species are restricted to certain areas by ambient temperatures, so climate change has likely allowed these species to move into new habitats.
Many recent changes in organisms have been chalked up to climate change. Which of those represent adaptation and which represent phenotypic plasticity? Here are a few examples from each category:
Adaptation:
Canadian squirrels have evolved earlier breeding times. Squirrels with genes for earlier breeding were probably favored because this allows them to take advantage of an earlier spring and hoard more pinecones for winter survival.
A North American mosquito species has evolved to wait longer before going dormant for the winter. Mosquitoes with genes that cause them to go dormant later were probably favored because it allows the insects to gather more resources during our new, extra-long summers.
Plasticity:
Some plant species around Walden Pond are flowering as much as three weeks earlier than they did 150 years ago. In these species, flowering is partly triggered by temperature, so climate change is the likely cause of this shift.
Most butterfly species in central California have been taking flight about 24 days sooner in comparison to 30 years ago. When butterfly species mature is closely related to temperature, so climate change is the likely cause of this shift
Alpine plant species in Austria and Switzerland have changed their range and are now found at higher altitudes than they were 100 or so years ago. Many plant species are restricted to certain areas by ambient temperatures, so climate change has likely allowed these species to move into new habitats.
Principle 3b
Greenhouse Gases Make the Earth Habitable
Heat-trapping greenhouse gases are not all bad.
In fact, their presence in small amounts in the atmosphere makes life on Earth possible. That’s because they warm the Earth's surface, resulting in a planet that sustains liquid water and life.
Earth is the Goldilocks planet: “not too hot, not too cold, but just right” for liquid water to exist. Read more…
Greenhouse Gases Make the Earth Habitable
Heat-trapping greenhouse gases are not all bad.
In fact, their presence in small amounts in the atmosphere makes life on Earth possible. That’s because they warm the Earth's surface, resulting in a planet that sustains liquid water and life.
Earth is the Goldilocks planet: “not too hot, not too cold, but just right” for liquid water to exist.
If it weren’t for the planet’s greenhouse effect and what some scientists have described as its "self-regulating” nature, the planet would be frozen, and life as we currently know it wouldn’t exist.
Photosynthesis, which involves two heat trapping gases, CO2 and H2O, generates carbon-based sugars that form the base of the food chain. It also provided the starting material for the generation of fossil fuels. Photosynthesis is the often-overlooked process linking carbon, climate and energy.
Principle 3c
Changes in the Climate can Affect Ecosystems
Changes in the climate can affect the health of ecosystems and the survival of entire species.
The distribution patterns of fossils show evidence of gradual as well as abrupt extinctions related to climate change in the past.
The Earth has experienced at least five major mass extinctions in the past when the climate and/or environment shifted.
Some scientists suggest we are in the midst of another mass extinction, this one caused by human-caused climate change.
Over billions of years, organisms have been able to adapt to and evolve with the changing circumstances. But changes, especially in terms of temperature and precipitation, can spell the end of individual organisms and sometimes entire species.
Read More…
Changes in the Climate can Affect Ecosystems
Changes in the climate can affect the health of ecosystems and the survival of entire species.
The distribution patterns of fossils show evidence of gradual as well as abrupt extinctions related to climate change in the past.
The Earth has experienced at least five major mass extinctions in the past when the climate and/or environment shifted.
Some scientists suggest we are in the midst of another mass extinction, this one caused by human-caused climate change.
Over billions of years, organisms have been able to adapt to and evolve with the changing circumstances. But changes, especially in terms of temperature and precipitation, can spell the end of individual organisms and sometimes entire species.
Roughly 251 million years ago, an estimated 70 percent of land plants and animals died, along with 84 percent of ocean organisms—an event known as the “End Permian extinction”. The cause is unknown but it is known that this period was also an extremely warm one. A new analysis of the temperature and fossil records over the past 520 million years reveals that the end of the Permian is not alone in this association: global warming is consistently associated with planet-wide die-offs.
"There have been three major greenhouse phases in the time period we analyzed and the peaks in temperature of each coincide with mass extinctions," says ecologist Peter Mayhew of the University of York in England, who led the research examining the fossil and temperature records.
Pairing these data—the relative number of different shallow sea organisms alive during a given time period and the record of temperature—reveals that eras with relatively high concentrations of greenhouse gases bode ill for the number of species on Earth. "The rule appears to be that greenhouse worlds adversely affect biodiversity," Mayhew says.
That also bodes ill for the fate of species currently on Earth as the global temperatures continue to rise to levels similar to those seen during the Permian. "The risk of future extinction through rapid global warming is expected to occur through mismatches between the climates to which organisms are adapted in their current range and the future distribution of those climates.”
That is not to say that global warming was the cause of this Permian wipeout or that all mass extinctions are associated with warmer worlds—witness the disappearance of 60 percent of different groups of marine organisms during the cooling at the end of the Ordovician period roughly 430 million years ago.
But these scientists argue that the evidence of a link between climate change and mass extinctions gives reason to be concerned for the future. "We need to know the mechanism behind the associations and we need to know if associations of this sort also occur in shorter-term climatic fluctuations," Mayhew says. "That will help us decide if this is really a worry for the next generation or if the threat is merely a distant future threat."
Source: Scientific American: http://www.scientificamerican.com/article/mass-extinctions-tied-to-past-climate-changes/
Preventing the Sixth Mass Extinction Requires Dealing With Climate Change Photo credit: David Smith, University of California Museum of Paleontology
Source: Huffington Post: Posted: 11/18/2014 7:37 pm EST Updated: 01/18/2015 5:59 am EST
Last week the United States and China signed a landmark agreement to combat climate change. This is an important step in guarding against even more damage from rising seas that threaten major cities, increasingly common and severe storms that devastate lives and property, wildfires, drought, and the huge economic costs that already are mounting from climate catastrophes.
However, from my perspective as a paleontologist who has spent decades studying the impacts of climate change, both before and after people got into the act, there is an even bigger reason to forge global climate agreements. Allowing the climate change we're now causing to continue would virtually guarantee that human beings will be the first species in the planet's history bring on a mass extinction of life on Earth.
Mass extinction means that at least three out every four species you are familiar with die out. Forever. Extinction of that magnitude has happened only five times in the past 540 million years, most recently 66 million years ago, when the last big dinosaurs were killed by an asteroid strike.
Today, even without human-caused climate change thrown into the mix, most scientists agree that we — Homo sapiens — have been pushing the world towards the sixth mass extinction from such long-recognized human pressures as habitat destruction (for instance from deforestation or pollution), poaching, and overfishing. The magnitude of those pressures is overwhelming when you start to think on the global scale. We've completely plowed, paved, or otherwise transformed 50 percent of Earth's lands, taking all those places out of play for the species that used to live there. With 7 billion of us (and more added every day) on the planet, the human race now takes more than a third of all the energy produced by plant photosynthesis — so-called net primary productivity — just to support itself. That means a third less energy is available to sustain life for all the other species on the planet.
The International Union for the Conservation of Nature has determined that, as a result of such pressures, at last count, well over 20,000 species are now threatened with extinction. That is more than a quarter of all evaluated species. Of course, the actual number of species hanging on by a thread is likely much higher, given that many species have not even been evaluated yet.
Adding today's human-caused climate change -- and especially the accelerated changes projected under business-as-usual scenarios -- into the milieu of extinction drivers is like adding a match to gasoline. One reason is that the planet is rapidly heating up to a temperature that most species on Earth today have never experienced. For example, never in the 160,000-year history of the human species have we seen an Earth as hot as it will be by mid-century. Keep that warming going until the year 2100 and Earth would be hotter than it has been in the past 14 million years; that is the trajectory we are now on. Most species alive today, however, have only evolved to cope with climatic conditions that have existed over the past 2 million years.
The rapidity of human-caused climate change is the second big problem causing extinctions. Today, climate is changing at least 10 times more quickly than living species have ever experienced in their evolutionary history. That means that evolving to cope with the newly emerging climatic conditions is not an option for most species, because evolution has a speed limit usually reckoned in thousands to millions of years. Evolving to meet such a severe climate challenge over a hundred years or so simply exceeds most species' adaptive capacity, ultimately because genetic mutation rates are so slow. The exceptions — the adaptive winners in the climate change game, if you will — are species that reproduce quickly and in prodigious numbers, like flies, mosquitoes, rats, and mice.
Easier than adapting, of course, is simply up and moving, which species have been known to do during past times of climate change, though none of those past climate changes was as rapid as what is happening today. But even in cases where species could theoretically run quickly enough, on today's landscape, and especially given the shifting climatic regimes of the coming decades, there is nowhere to run to. Not only are the few remaining patches of habitat that contain diverse species separated by impenetrable human-modified and human-dominated landscapes and seascapes, but ongoing climate change promises to steal the very habitats that now support most species on the planet. On land, as much as two thirds of all species live in tropical and subtropical forests, yet climate models indicate that by the time babies today are middle-aged, the climate required to support those tropical and subtropical species will disappear over large swaths of the lands where they currently live and will be found nowhere on Earth.
In the oceans, it looks every bit as grim if we do nothing to slow climate change. Both experimental and modeling research indicates that warming waters and the other byproduct of elevated greenhouse gases, rising acidity in the oceans, would likely cause coral reefs to disappear almost entirely by 2070. These "rainforests of the sea" support 25 percent of all the ocean's species -- and 10 percent of the world's fisheries, which provide the principal protein for hundreds of millions of people and inject billions of dollars per year into the world economy.
Avoiding such dire scenarios requires a multi-pronged effort to address all known extinction drivers -- including protecting remaining habitats, halting poaching, cleaning up pollution, slowing and stabilizing human population growth, and ascribing economic value to biodiversity in general and to keeping species like elephants and tigers alive rather than selling their bodies for parts. And indeed, efforts focused in those directions have proven successful in bringing some species back from the brink.
But human-caused climate change has fundamentally changed the extinction game to one we are destined to lose if we simply continue business as usual. The only way to prevent the extinction of thousands of species will be to slow greenhouse warming dramatically, which requires rapidly shifting from a fossil-fuel economy to one dominated by carbon-neutral energy. Numerous analyses have shown the technology and expertise exists to make this possible. All that's standing in the way is deciding it's the right thing to do.
It is still unclear whether the world is ready to do anything about climate change. The follow-up to last week's historic climate agreement between the United States and China will be telling. And while it's appropriate that world leaders are weighing the immediate human impacts against the costs of climate action, it's also essential that they, and the rest of us, see the bigger picture. The most critical accounting needs to be reckoned in lives, not only of individuals but of entire species. That accounting under a business-as-usual scenario rapidly adds up to the sixth mass extinction. And, while many impacts of climate change may come and go and vary from place to place, extinction is forever.
Anthony D. Barnosky is a professor in the Department of Integative Biology, a curator at the Museum of Paleontology, and a research paleoecologist at the Museum of Vertebrate Zoology at the University of California, Berkeley. His new book, Dodging Extinction: Power, Food, Money, and the Future of Life on Earth (University of California Press, fall 2014) explains how we can get climate change and other extinction drivers under control to avoid the sixth mass extinction. He also talks about these issues in the upcoming film Mass Extinction: Life on the Brink, to be released on the Smithsonian Channel Nov. 30.
Q
9 animals that are feeling the impacts of climate change
Climate change is one of the greatest challenges of our time. We are already seeing its effects with rising seas, catastrophic wildfires and water shortages. These changes are not only having a dramatic impact on diverse ecosystems but also on the wildlife that call these places home. Here are 9 species that are already being affected by climate change.
If we don’t act on climate now, this list is just the tip of the iceberg of what we can expect in years to come. Future generations shouldn’t just see these animals in history books -- we owe it to them to protect these creatures and their habitats.
1. Moose
Rising temperatures and booming parasite populations are expected to cause this cold-weather species that calls the northern United States and Canada home to move farther north. That’s because milder winters and less snow can lead to higher numbers of winter ticks. Tens of thousands of these parasites can gather on a single moose to feed on its blood -- weakening the animal’s immune system and often ending in death, especially the calves. Photo by National Park Service.
2. Salmon
Salmon require cold, fast-flowing streams and rivers to spawn. Changing stream flows and warming waters in the Pacific Northwest are already impacting some salmon species and populations. Higher temperatures have also led a harmful salmon parasite to invade Alaska’s Yukon River. So while salmon might currently be on the menu, climate change is expected to impact major commercial and recreational fishing industries in the coming years. Photo by Bureau of Land Management.
3. Snowshoe Hares
To help hide from predators, this North American rabbit has evolved to turn white in winter to blend in with the snow. With climate change, snow in some areas is melting earlier than the hares have grown accustomed to, leaving stark white hares exposed in snow-less landscapes. This increased vulnerability might cause declines in hare populations that could lead to implications for other species. Snowshoe hares are critical players in forest ecosystems. Photo by National Park Service.
4. American Pikas
About the size and shape of a hamster, the American pika typically lives at high elevations where cool, moist conditions prevail. Research by U.S. Geological Survey has found that pika populations are now disappearing from numerous areas that span from the Sierra Nevadas to the Rocky Mountains. Populations within some areas are migrating to higher elevations likely to avoid reduced snowpacks and warmer summer temperatures. Unfortunately, pikas are strongly tied to rocky-talus habitat that is limited and patchily distributed. This gives them few options as temperatures continue to rise. Photo by Jon LeVasseur (www.sharetheexperience.org).
5. Sea Turtles
Various populations of sea turtle species and their nesting sites are vulnerable to sea-level rise, increased storminess and changing temperatures -- all impacts of climate change. These factors may result in current nesting and foraging sites becoming unsuitable for federally threatened and endangered turtle species -- especially loggerhead sea turtles. Photo by USGS.
6. Puffins
These colorful-billed birds that look like miniature penguins are experiencing population declines in the United States and elsewhere. In the Gulf of Maine, puffins are having difficulty finding their major food sources of white hake and herring. As the sea warms, the fish are moving into deeper waters or further north, making it harder for puffins to catch a meal and feed their young. Adult puffins are compensating by feeding their young butterfish, but young puffins are unable to swallow these large fish and many are dying of starvation. Delayed breeding seasons, low birth rates and chick survival are all affecting the reproductive ability of these birds. Photo by USFWS.
7. Alaskan Caribou
Caribou are always on the move -- it’s not uncommon for them to travel long distances in search of adequate food. But as temperatures increase and wildfires burn hotter and longer in Alaska, it could considerably change the caribou’s habitat and winter food sources. Ultimately, this will affect subsistence hunters who rely on caribou for nutritional, cultural and economic reasons. Photo courtesy of Jacob W. Frank.
8. Piping Plovers
The piping plover is an iconic shorebird that breeds and nests along the Atlantic Coast, the Great Lakes and the Great Plains. Increased human use of their beach habitats, including intense coastal development, as well as rising sea levels and storm surges associated with climate change threaten the species. Photo by USFWS.
9. Polar Bears
Polar bears in many ways have become the symbol of climate change. In 2008, they were listed as a threatened species under the Endangered Species Act -- the first species to be listed because of forecasted population declines from the effects of climate change. The primary cause of their decline: loss of sea ice habitat attributed to Arctic warming. Polar bears need sea ice to hunt seals -- a main source of food -- as well as to move across the large home ranges they need for foraging habitat. Polar bears aren’t alone in feeling the effects of shrinking sea ice. Walruses and other Arctic species are facing similar challenges as summer sea ice continues to retreat. Photo by National Park Service.
Learn more about Interior's work on climate change at www.doi.gov/climate.
Q
Principle 3d
Over Most of the Last 10,000 Years, the Climate has been Unusually Stable
A range of natural records shows that the last 10,000 years have been an unusually stable period in Earth's climate history.
Modern human societies developed during this time.
The agricultural, economic, and transportation systems we rely upon are vulnerable if climate changes significantly. Read More…
Over Most of the Last 10,000 Years, the Climate has been Unusually Stable
A range of natural records shows that the last 10,000 years have been an unusually stable period in Earth's climate history.
Modern human societies developed during this time.
The agricultural, economic, and transportation systems we rely upon are vulnerable if climate changes significantly.
The “Holocene”, the geological epoch that began roughly 11,700 years ago, is an interglacial (warm) period in the current ice age (an interglacial period is geological interval of warmer global average temperature lasting thousands of years that separates consecutive glacial periods within an ice age).
The Holocene has been relatively steady in terms of climate. During the Holocene, human societies began to settle into communities. They engineered water systems for use in agriculture. They developed commerce, weapons systems, smelting metals, and harnessing animals. All thanks in large part to a relatively stable climate.
Humans have always been vulnerable to severe weather and changes in climate. The Vikings settled in Greenland during a brief warm period there but died off or retreated when the climate turned colder again. Droughts have been linked as a key component in the breakdown of entire societies, and there is some evidence that a megadrought in the 16th Century in Mexico triggered an epidemic of hemorrhagic fever that killed between five and fifteen million people.
During the Holocene the human population grew from a few million people around the planet to several hundred million people two thousand years ago. By around 1800 there were a billion people. By the mid 1950s, it had risen to three billion. In the past fifty years the population has more than doubled and it will continue to grow until, whether by circumstances or design, there are fewer people being born than are dying.
The exponential population growth, fueled in part by the exponential growth in the use of fossil fuels, has also led to more people being put in harm’s way through “disasters by design”, such as building in floodplains and along coastlines. Today more than half the U.S. population lives on or near the coasts, which are vulnerable to coastal storms and sea level rise.
Climate change and drought in the American Southwest
Rudy Baum | October 2015
Source: http://climate.org/effects-of-21st-century-climate-change-on-drought-disk-in-the-american-southwest/
Introduction
Drought is a common occurrence in the American Southwest. Since the beginning of the 20th century, the region has experienced four major multiyear droughts: the Dustbowl (1929-1940), the Southwest/Great Plains drought (1946-1956), a turn-of-the-century drought that lasted from 1999-2005, and the ongoing 2012-2015 drought. Other, shorter dry spells occurred during the same period as well.
During the current drought, many states in the region have seen record or near-record persistent high temperatures, as well as extreme lows in precipitation, streams flows, and soil moisture. California has been hit especially hard. 2012-2015 have been the driest four years in the state’s recorded history, and in 2015 the Sierra Nevada snowpack hit a 500-year low. Drought conditions in California in 2014 represented a 200-year event, while the cumulative 2012-2015 drought may be completely unprecedented within the past 10,000 years.
There is a strong consensus that rising global temperatures forced by anthropogenic CO2 emissions will increase the frequency, intensity, and duration of droughts across the American Southwest. Increased evaporation due to warmer surface temperatures and decreased precipitation will drive significant reductions in soil moisture across the region. This poses serious environmental and economic risks for the Southwest. Between 1980 and 2003, droughts caused an estimated $190 billion dollars in economic damage across the United States (adjusted to 2015 dollars), making it the most costly form of natural disaster over that period. Droughts can decrease the amount of water available for agriculture, reduce power generating capacity, and increase the risk of forest fires. Between growing demand for water and the predicted increase in drought frequency, the Southwest’s water infrastructure may struggle to adapt to a new, drier climate regime.
Climate and Paleoclimate of the Southwest
The American Southwest covers over four million square kilometers. Four of western North America’s major watersheds lie within its boundaries: the Colorado River basin, the Rio Grande basin, the Sacramento-San Joaquin watershed, and most of the Great Basin. Annual mean precipitation across much of the region ranges between 10 and 60 centimeters per year, low enough to qualify as arid or semi-arid. Some areas, such as the Sierra Nevada in California and the high peaks of the Colorado Plateau, receive significantly more precipitation, mostly in the form of large quantities of snow. Much of the Southwest’s summer water supply comes from the melting of these alpine snowpacks.
The combination of low annual precipitation and hot, dry summers makes the Southwest especially drought-prone. 10-15% of the years between 1895 and 1995 saw severe or extreme drought conditions in the region. At most, these modern droughts last about ten years; however, reconstructions of the Southwest’s paleoclimate have shown that the region is also susceptible to extraordinary megadroughts that can last for decades or even centuries. A fifty-year drought struck the Southwest, Northern Mexico, and the Rocky Mountains between about AD 1540 and 1590, which contributed to the abandonment of nearly a dozen native pueblos and may have aggravated an outbreak of an unknown, indigenous hemorrhagic virus that killed 7 to 17 million people. Three hundred years before, the Great Drought of AD 1267-1299 was at least partially responsible for the abandonment of Ancestral Pueblo sites throughout the Colorado Plateau.
Some of the most severe megadroughts to strike the Southwest occurred in California. Between about AD 1250 and 1350, a century-long drought struck the Sierra Nevada region. Another, longer drought in the region has also been identified between AD 900 and 1100, although subsequent research has suggested that this earlier interval may not have been a single, uninterrupted drought, but rather a series of decade-long droughts following one after another. Precipitation was so low during this period that the shorelines of many lakes throughout the Sierra Nevada were tens of meters lower than they are today, which allowed mature pine trees to grow for decades in areas that today are underwater. These century-scale droughts caused significant disruptions for native cultures in California and the Great basin, leading to major migrations, site abandonments, and the collapse of long-distance trade routes.
Both the California megadroughts and the Great Drought (which was part of a larger pattern of increased aridity in the Colorado Plateau) occurred during a period of elevated global temperatures known as the Medieval Climate Anomaly. In both cases, the droughts were caused by persistent, anomalously cold sea surface temperatures in the eastern Pacific consistent with the La Niña phase of the El Niño-Southern Oscillation (ENSO).
Causes of Future Drought
Although drought is often thought of as the result of a shortfall in precipitation, most studies of drought instead look at deficits in the total moisture content of soils. Drought is therefore most often measured by comparing moisture supply into soils (precipitation) minus moisture demand from soils (evaporation).
21st century drought in the Southwest will primarily be driven by increased evaporation due to warmer global surface temperatures. Relative humidity will decrease as temperatures rise, which will lead to increased evaporative demand from soils. Enhanced evaporation due to global warming will reduce soil moisture in the Southwest by an average of 3 cm/year. By 2099, soils in the region will be 10-20% drier than they are today, which will increase the risk of drought by at least 20%.
One of the characteristic features of climate change is that, for almost all weather phenomena, the risk of extreme events increases more quickly than it does for moderate events. Accordingly, the risk of a severe, multidecade drought occurring in the Southwest between 2050 and 2099 is more than 80% greater than it is today. Soil desiccation will be exacerbated by an increased likelihood of extreme daily high temperatures. Extreme hot days are already five times more likely than they were prior to the Industrial Revolution, and with another 1°C of warming they will become five times again more likely. In some cases, evaporative demand from warmer surface temperatures will exceed available soil moisture—in other words, there will be periods in the coming century during which some soils in the Southwest dry out completely. This excessive drying may feed back into even warmer surface temperatures: there is evidence that as soil moisture content reaches zero, the loss of cooling heat fluxes due to evaporation will cause additional warming.
Changes in precipitation will also play a role in determining the future severity of drought conditions in the Southwest, although not as great as that of evaporation. As the planet warms, the downward arms of the Hadley Cells will expand poleward. Hadley Cells are a form of atmospheric circulation where air rises at the equator and descends at about 30° latitude on either side (about the latitude of the U.S.-Mexico border in North America). The downward arms of the Hadley Cells are associated with high atmospheric pressure and arid climates. Hadley cell expansion over the American Southwest is predicted to decrease precipitation there by 3-15% by the end of the 21st century. The increased high atmospheric pressure over the region will also reduce cloud formation, which will worsen evaporation by allowing more solar energy to reach earth’s surface. The decrease in overall precipitation will be exacerbated by changes in the way precipitation falls: more intense, less frequent precipitation will lead to longer dry spells. Increased winter rains, reduced snow packs, and earlier snow melts will also lead to less moisture being available during summer months, when evaporation is most intense.
One major source of uncertainty in predicting future Southwestern droughts is the response of ENSO to rising global temperatures. La Niña (the cool or negative phase of ENSO), which is characterized by cool sea surface temperatures in the eastern equatorial Pacific Ocean, is strongly associated with drought conditions across the American Southwest. Indeed, the megadroughts of the 11th-13th centuries are thought to have been caused by unusually persistent La Niña-like conditions. However, it is unclear how ENSO will react to a warming climate. Climate models are split over whether ENSO will become more intense, or remain relatively unchanged. There is also the possibility that ENSO will evolve non-linearly over the course of the 21st century, initially becoming more intense before returning to normal variability after 2040. The uncertainty surrounding ENSO’s response to global warming thus makes it difficult to predict the precise details of future climate regimes in the Southwest.
Predicted Effects
As global temperatures continue to rise, perhaps by as much as 2-4°C by 2100, the Southwest will become increasingly dry. Average surface temperatures in the region have already risen by at least 1°C since the beginning of the 20th century. At present, record hot days are occurring at twice the rate of record cold days. By the end of the 21st century, much of the region will experience at least moderate drying. This will lead to significant changes in regional climate types and plant communities, with many temperate climate zones in the region transitioning to semi-aridity.
Changes in precipitation and evaporation will have significant impacts on snow pack levels, water availability, stream flow levels, and soil moisture. Warmer temperatures mean that more winter precipitation will fall as rain instead of snow. Earlier snowmelts have already been observed across the southwest, and in some basins rainwater has come to replace snowmelt as the dominant water source. Given that snowpack serves as a particularly important reservoir during the Southwest’s hot, dry summer months—snow melt accounts for between 30% and 75% of the region’s stream flows, depending on the basin—a decrease in total snowpack has serious economic consequences. Further, warmer temperatures will result in earlier snow melts, which in turn will lead to earlier peak stream flows, as well as more extreme low flows later in the year. By the end of the 21st century, stream flows in the Sierra Nevada are predicted to drop at least 25% below their historical averages; essentially every stream in the Colorado River basin will have below-normal summer flows, with many previously perennial streams developing intermittent flows; and the Rio Grande’s upper basin will see total stream flow reductions of over 400 million m3/year.
The economic and environmental impacts of increased Southwestern drought are substantial. The Colorado River is a major source of drinking water for 40 million people, while the Sierra Nevada snowpack, which accounts for 30% of California’s water supply, is a crucial reservoir not just for the state’s 38 million residents, but its lucrative agricultural industry as well. The 2012-2015 drought has cost California’s economy $2.74 billion (with $1.84 billion in losses coming from the agricultural industry alone) and 21,000 jobs. As surface water supplies decrease, groundwater is being increasingly relied on to make up the difference. Faced with a surface-water deficit of 10.7 km3, California will extract 7.4 km3 of groundwater in 2015 alone. In the Colorado River basin, groundwater is currently being depleted at a rate of 5.6 km3/year. (Note that, as California draws some water from the Colorado River, there will be some overlap between these numbers.) Reduced stream flows also have implications for power generation in the Southwest. By the mid-21st century, hydropower capacity along the Colorado River and in California could drop by 2-5%.
On the environmental side, extended droughts may increase tree mortality, and, as a consequence, fuel loading in forests. This can lead to increased forest fire frequency and intensity, which can damage human health and property, as well as alter the ecological composition of burn areas. Research suggests that forest fires in the region are already becoming more common. Since 1986, the frequency of large-scale forest fires in the western United States has increased by a factor of four, and the total area burned has increased by a factor of six. Drought also imperils the viability of regional stream ecologies. As a result of increased surface temperatures and low stream flows, warmer annual mean temperatures are predicted in many streams across the Southwest. This could prove especially damaging for coldwater fish species such as trout. Total suitable habitat for all trout species found in the American west could decline by 47% by the end of the 21st century.
Conclusion
Drought is a regular feature of the American Southwest’s climate regime, as can be seen in both the modern record, and through reconstructions of the region’s paleoclimate. Over the course of the 21st century, the Southwest will experience significant increases in drought frequency and overall aridity as a result of human-caused global warming. Warmer surface temperatures will increase evaporative demand, leading to reduced soil moisture content. Decreased precipitation across the region will also contribute to the increase in drought frequency, although its role will be secondary to that of evaporation. The effects of increasing regional aridity are expected to include changes in plant communities, reduced snowpacks and earlier snow melt, lower stream flows, warmer stream temperatures (Reynolds 2015), increased groundwater extraction, reduced hydropower generating capacity, increased tree mortality, and increased wildfire risk.
In short, in the future the American Southwest will be hotter and drier than it is today. Drought conditions, as defined relative to 20th century averages, will become the norm—a permanent drought, in essence. There will still be wet years, as well as some truly exceptional dry years, but that natural variability will fluctuate around a mean climate state that, overall, will be much drier than the previous century’s.
Human adaptation to a dryer Southwest will be a challenging proposition. As populations throughout the Southwest continue to grow, so too will the demand placed on the region’s diminishing water resources. The Southwest is a marginal landscape, characterized by rugged terrain, low precipitation, and high summer temperatures, and civilization in the region has often balanced on a hydrological knife edge. Within the past 1,000 years, several severe, multidecade droughts have struck the region, causing societal collapse, mass migrations, and in extreme cases perhaps even widespread human mortality. Future droughts in the region will be as or more severe than the megadroughts of the past. Due to its wealth, the United States has substantial capacity for climate change adaptation, but the scale of the challenges facing the Southwest in the coming century should not be underestimated. In the past, native civilizations in the region experienced major societal reorganizations or even collapsed in the face of severe, long-term aridification—civilizations that, although less technologically advanced than the modern United States, were nevertheless very well adapted to life in the water-scarce Southwest. The possibility that climate change will fundamentally alter the economy and social structure of the Southwest cannot be ignored.
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- Fischer EM, Beyerle U, Knutti R. 2013. Robust spatially aggregated projections of climate extremes. Nature Climate Change 3: 1033-1038.
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Q
Earth's Climate History: Implications for Tomorrow
By James E. Hansen and Makiko Sato — July 2011
Humans lived in a rather different world during the last ice age, which peaked 20,000 years ago. An ice sheet covered Canada and parts of the United States, including Seattle, Minneapolis and New York City. The ice sheet, more than a mile thick on average, would have towered over today's tallest buildings. Glacial-interglacial climate oscillations were driven by climate forcings much smaller than the human-made forcing due to increasing atmospheric CO2 — but those weak natural forcings had a long time to operate, which allowed slow climate feedbacks such as melting or growing ice sheets to come into play.
The past is the key to the future. Contrary to popular belief, climate models are not the principal basis for assessing human-made climate effects. Our most precise knowledge comes from Earth's paleoclimate, its ancient climate, and how it responded to past changes of climate forcings, including atmospheric composition. Our second essential source of information is provided by global observations today, especially satellite observations. which reveal how the climate system is responding to rapid human-made changes of atmospheric composition, especially atmospheric carbon dioxide (CO2). Models help us interpret past and present climate changes, and, in so far as they succeed in simulating past changes, they provide a tool to help evaluate the impacts of alternative policies that affect climate.
Paleoclimate data yield our best assessment of climate sensitivity, which is the eventual global temperature change in response to a specified climate forcing. A climate forcing is an imposed change of Earth's energy balance, as may be caused, for example, by a change of the sun's brightness or a human-made change of atmospheric CO2. For convenience scientists often consider a standard forcing, doubled atmospheric CO2, because that is a level of forcing that humans will impose this century if fossil fuel use continues unabated.
We show from paleoclimate data that the eventual global warming due to doubled CO2 will be about 3°C (5.4°F) when only so-called fast feedbacks have responded to the forcing. Fast feedbacks are changes of quantities such as atmospheric water vapor and clouds, which change as climate changes, thus amplifying or diminishing climate change. Fast feedbacks come into play as global temperature changes, so their full effect is delayed several centuries by the thermal inertia of the ocean, which slows full climate response. However, about half of the fast-feedback climate response is expected to occur within a few decades. Climate response time is one of the important 'details' that climate models help to elucidate.
Figure 1: Global temperature relative to peak Holocene temperature, based on ocean cores.
We also show that slow feedbacks amplify the global response to a climate forcing. The principal slow feedback is the area of Earth covered by ice sheets. It is easy to see why this feedback amplifies the climate change, because reduction of ice sheet size due to warming exposes a darker surface, which absorbs more sunlight, thus causing more warming. However, it is difficult for us to say how long it will take ice sheets to respond to human-made climate forcing because there are no documented past changes of atmospheric CO2 nearly as rapid as the current human-made change.
Ice sheet response to climate change is a problem where satellite observations may help. Also ice sheets models, as they become more realistic and are tested against observed ice sheet changes, may aid our understanding. But first let us obtain broad guidance from climate changes in the 'recent' past: the Pliocene and Pleistocene, the past 5.3 million years.
Figure 1 shows global surface temperature for the past 5.3 million years as inferred from cores of ocean sediments taken all around the global ocean. The last 800,000 years are expanded in the lower half of the figure. Assumptions are required to estimate global surface temperature change from deep ocean changes, but we argue and present evidence that the ocean core record yields a better measure of global mean change than that provided by polar ice cores.
Civilization developed during the Holocene, the interglacial period of the past 10,000 years during which global temperature and sea level have been unusually stable. Figure 1 shows two prior interglacial periods that were warmer than the Holocene: the Eemian (about 130,000 years ago) and the Holsteinian (about 400,000 years ago). In both periods sea level reached heights at least 4-6 meters (13-20 feet) greater than today. In the early Pliocene global temperature was no more than 1-2°C warmer than today, yet sea level was 15-25 meters (50-80 feet) higher.
The paleoclimate record makes it clear that a target to keep human made global warming less than 2°C, as proposed in some international discussions, is not sufficient — it is a prescription for disaster. Assessment of the dangerous level of CO2, and the dangerous level of warming, is made difficult by the inertia of the climate system. The inertia, especially of the ocean and ice sheets, allows us to introduce powerful climate forcings such as atmospheric CO2 with only moderate initial response. But that inertia is not our friend — it means that we are building in changes for future generations that will be difficult, if not impossible, to avoid.
Figure 2: Greenland (a) and Antarctic (b) mass change deduced from gravitational field measurements by Velicogna (2009) and best-fits with 5-year and 10-year mass loss doubling times.
One big uncertainty is how fast ice sheets can respond to warming. Our best assessment will probably be from precise measurements of changes of the mass of the Greenland and Antarctic ice sheets, which can be monitored via measurements of Earth's gravitational field by satellites.
Figure 2 shows that both Greenland and Antarctic ice sheets are now losing mass at significant rates, as much as a few hundred cubic kilometers per year. We suggest that mass loss from disintegrating ice sheets probably can be approximated better by exponential mass loss than by linear mass loss. If either ice sheet were to lose mass at a rate with doubling time of 10 years or less, multi-meter sea level rise would occur this century.
The available record (Fig. 2) is too brief to provide an indication of the shape of future ice mass loss, but the data will become extremely useful as the record lengthens. Continuation of these satellite measurements should have high priority.
References
Hansen, J.E., and Mki. Sato, 2011:Paleoclimate implications for human-made climate change.In Climate Change: Inferences from Paleoclimate and Regional Aspects.A. Berger, F. Mesinger, and D. Šijači, Eds. Springer, in press.
Velicogna, I., 2009: Increasing rates of ice mass loss from the Greenland and Antarctic ice sheets revealed by GRACE. Geophys. Res. Lett., 36, L19503, doi:10.1029/2009GL040222.
Q
Principle 3e
Life on Earth is a Major Driver of the Global Carbon Cycle
click the image to enlarge it and read about stromatolites
It does so by modifying the chemical makeup of the atmosphere. The geologic record shows that life has significantly changed the atmosphere during Earth's history.
Life on Earth is a Major Driver of the Global Carbon Cycle
Life — everything from microbes to humans — is a major driver of the global carbon cycle and can influence global climate.
It does so by modifying the chemical makeup of the atmosphere. The geologic record shows that life has significantly changed the atmosphere during Earth's history.
Beginning over a billion years ago, organisms like algae and photosynthesizing bacteria captured solar energy and transformed it into carbohydrates, pumping out oxygen and removing CO2 from the atmosphere in the process (click on the photo above to see some of the fossils of those billion-year-old bacteria—they are called stromatolites—in Glacier National Park).
Later, plants evolved and removed even more CO2. Under the right geologic conditions of time and pressure, these carbohydrates turned into hydrocarbons, which we use today for fuels (we call them fossil fuels). The combustion of fossil fuels, as super concentrated forms of “buried solar energy” in effect reverses the process of photosynthesis.
Therefore, living things link to climates of the past while impacting climate in the future.
Living things also affect the reflectance of the Earth's surface, which can impact Earth's energy balance.
Stromatolites in Glacier Park
Some of the best known fossils are found on the east side of the park, which is composed of nearly 1.5 billion year old limestone. Here we find massive beds of stromatolites, fossils of bacteria that formed in the bottoms of shallow, warm seas and through photosynthesis, created the oxygen rich atmosphere we live in today.
Life Makes a Mark
Source: American Museum of Natural History
http://www.amnh.org/explore/science-bulletins/earth/documentaries/the-rise-of-oxygen/article-life-makes-a-mark
Consider the forces that have shaped planet Earth over time, and one tends to picture the grand geophysical events: earthquakes and volcanoes, erosion by wind and water, the drift of continental plates, the warming and cooling of the global climate. But there is another crucial force, microscopic in size yet global in its impact: the microbe.
Single-celled microscopic organisms—microbes—are the oldest and most abundant form of life on Earth. The term "microbes" spans a bewildering range of life-forms, from plants to animals to the ambiguously classified fungi. And microbes occupy an astonishing range of habitats, from the familiar (your shower curtain) to the most forbidding (inside volcanoes on the seafloor). In 1683, Antoni van Leeuwenhoek, the first scientist to view living bacteria through a microscope, exclaimed: "There are more animals living in the scum on the teeth in a man's mouth than there are men in a whole kingdom."
Since their first emergence on Earth perhaps more than 3.8 billion years ago, microbes have dramatically altered the chemistry of the atmosphere and, with it, the planet's surface. Among the countless kinds of microbes that have evolved, none have quite equaled the accomplishments of the first cyanobacteria (the stromatolites in Glacier National Park in Montana and in the Mission Mountains were formed by stromatolites). These organisms were photosynthetic organisms that, like plants, drew on the Sun's energy to create oxygen, and in doing so helped create an oxygen-rich atmosphere. Earth today is habitable to multicellular creatures like us largely because cyanobacteria made it so. "One cannot separate the study of Earth's early atmosphere from the study of the evolution of life on this planet," says Jay Kaufman, a geoscientist at the University of Maryland. "They are intimately linked."
Wherever they may live, microbes thrive on basic chemistry. Think of them as molecular scrap-metal workers: They take apart commonplace chemical compounds and reassemble the individual parts, or ions, into altogether different molecules. For example, phytoplankton, microscopic plants that flourish near the ocean surface, convert carbon dioxide (CO2) and water (H2O) into carbohydrates and oxygen (O2). Though small in size, these microbes are so abundant that they generate half the oxygen we breathe.
What does a microbe earn for its labors? An infusion of energy, gained through the handling of miniscule, negatively charged particles called electrons. Every atom is surrounded by electrons, which help bind atoms together into molecules. As molecules are broken down and reformed, their electrons are exchanged and redistributed. A microbe, in the course of reshuffling ions and molecules, siphons off an electron or two for itself, to be used later in still other chemical reactions in its pursuit of food and energy. The molecules it generates, meanwhile, can become fodder for all sorts of other microbes. Leeuwenhoek was right: dental plaque is in fact an assembly line involving several species of bacteria, each playing a different role in the conversion of sugars and carbohydrates into cavity-causing acids. Your teeth are the platform for an entire atomic economy that runs on a currency of electrons.
Through eons of evolution, microbes have adopted impressive strategies to exploit and metabolize the many kinds of molecules that exist on Earth. The bacterium Pyrococcus furiosus thrives in the hot water that boils from undersea volcanic vents. This heat-loving microbe doesn't breathe oxygen; in fact, oxygen is toxic to it. Instead it takes in sulfur and releases hydrogen sulfide, the same gas that makes rotten eggs stink. This hydrogen sulfide is part of a bizarre seafloor food chain that never sees sunlight and includes creatures like albino clams and tubeworms.
A scrap-metal business thrives, or doesn't, depending on the availability of certain prized metal parts. So too with microbes. Oxygen-breathing organisms—microbes as well as larger, multicellular creatures like us—abound today only because there's plenty of atmospheric oxygen to breathe. Before about 2.4 billion years ago, when there was no atmospheric oxygen, different organisms, all of them microbial, dominated Earth. The sulfur-breathing bacterium P. furiosus is a descendant of the oldest branch of life, the Archaea, which some scientists believe may date back to that early oxygen-less era. Today, many Archaean microbes are relegated to murky, oxygen-free corners of the planet, including seafloor volcanoes and the intestines of cows.
Whatever a microbe produces—oxygen, methane, hydrogen sulfide—the task does require some effort, and the microbe must derive the initial energy to perform it from somewhere. Many scientists think that the earliest microbes derived their energy indirectly from Earth's internal heat, much as P. furiosus does today. Photosynthesis, the ability to convert the Sun's energy into microbial labor, developed somewhat later, perhaps as early as 3.5 billion years ago.
Photosynthesis was a major evolutionary invention, as it freed organisms from the ocean depths and enabled them to thrive just below the sea surface. But the greatest innovation was yet to come. Photosynthetic microbes, though able to utilize solar energy, were still restricted to the shallows; ultraviolet radiation from the Sun was so strong that nothing could live exposed on land. Then, around 2.7 billion years ago, a class of organisms called cyanobacteria appeared. Unlike their other photosynthetic cousins, these photosynthetic microbes produced oxygen. (To learn about the fossil evidence for cyanobacteria, watch the accompanying video "Early Fossil Life.")
The appearance of cyanobacteria signaled the beginning of a global transformation. Free oxygen began to accumulate in the atmosphere, forming two gases new to Earth. One was molecular oxygen (O2), well known to those of us who breathe it. The other was ozone (O3), a gas that forms high in Earth's atmosphere and, acting as a sort of global sunscreen, shields Earth's surface from the most harmful UV radiation. In the long run, the gradual rise of oxygen had two sensational effects: It permitted life to evolve on dry land, and it permitted the evolution of organisms that could thrive on oxygen. You can breathe easily, thanks to those early cyanobacteria.
"Imagine an early Earth that had no global sunscreen, no oxygen, hence no ozone," says Kaufman. "The production of oxygen through photosynthesis created that sunscreen. So biology actually made the surface environments habitable for future life by producing the oxygen we breathe today."
The role of microbes didn't end 2.4 billion years ago. Microscopic organisms are equally prevalent today, although they tend not to draw the same media attention that flashier, multicellular creatures do. And they're still churning out free oxygen, replenishing atmospheric O2 as quickly as other animals and chemical processes use it up. Like an earthquake or volcano, the lowly microbe is a planetary force to be reckoned with and respected.
"The atmosphere we have today is strongly influenced by biological activity," says Kaufman's colleague James Farquhar, a geochemist at the University of Maryland. "It's influenced by the types of gases that bacteria and other organisms produce. Life is critical in determining atmospheric composition, just as atmospheric composition is critical in controlling the conditions that are required to allow life to exist as it does."
Q
Principle 3f
Local Relevance
Coral With Leaves: Millions of Trees Joining the List of Climate Change Casualties
Mass die-offs in California and the Southwest are not only tied to global warming, they add to it
BY BOB BERWYN, INSIDECLIMATE NEWS
Just a few years after mountain pine beetles killed millions of acres of lodgepole pine forests in the Rocky Mountains, the U.S. Forest Service is reporting widespread tree deaths in drought-hammered Southern California. Even Europe's cool, moist forests have been losing trees at a fast rate. Large-scale simultaneous forest loss on different continents could have an impact on forests' ability to absorb atmospheric carbon, scientists say.
A recent aerial survey by the U.S. Forest Service tallied 26 million more dead trees in Southern and Central California between last October and April. In those six months, evergreen forests across 1,200 square miles—beset by drought and pine beetles—perished, transforming from living, breathing organisms into sticks of dead tinder and providing fuel for wildfires. In total, the agency has counted 66 million dead trees in the state since 2010.
"We're seeing almost an entire species lost, of the predominant species for this area," said Mariposa County Supervisor Kevin Cann, in a May 23 video by the California State Association of Counties. "It's inevitable that you want to deny this reality. You don't want to believe that your entire ponderosa forest can be wiped out. This summer, we're going to hold our breath for a while and try to be really prepared to react as fires happen."
Scientists have increasingly linked forest mortality with climate impacts—and in Southern California, it is most directly tied to a steady increase in droughts that weaken trees, making them more susceptible to pine beetles. A 2015 study in the journal Geophysical Research Letters found that human-caused warming "substantially increased the overall likelihood of extreme California droughts."
Widespread climate impacts to forests have also been documented in other regions, including the Southwest, and in Europe. Global forest mortality has potentially profound ecological and societal implications, given the importance of forests to everything from water supplies, wildlife habitat and food to the global carbon cycle. Collectively, the world's forests suck up about a quarter of human-caused carbon emissions.
"From a forester's perspective it is a catastrophe. Environmental services are under threat for an extended period of time," said Klaus Katzensteiner, a forest ecologist at the University of Vienna, Austria. In many places, he said the global forest changes will affect water flows and water quality, increase wildfire danger and alter the carbon balance of forests for a long time.
Drought is believed to be the main culprit in California, weakening millions of trees across the state. One study published in the Proceedings of the National Academy of Sciences shows how California forests lost huge amounts of water during the drought; another study in the International Journal of Wildland Fire shows the link between regional moisture deficits and wildfire activity.
Warmer temperatures since the 1980s have also enabled pine beetles to breed in record numbers. The insects lay their eggs beneath the bark of trees during the summer, introducing a fungus that interrupts the flow of moisture and nutrients from the roots to the rest of the tree. Within a year, the trees die.
Pine beetles and related insects are native to forests and play an important ecological role by killing older trees to make way for new growth. In the past, their populations have been checked by extreme cold in winter. But in recent decades, those cold periods have been less common in many mountain regions. More larvae survive the winter and get a head start on attacking new trees earlier in the spring. Warmer temperatures have also enabled the insect to spread to higher elevations and, in some areas, to breed more than once a year.
In 2002, then a record-warm year for the planet, ips beetles started to spread across the Southwest and within two years, they killed nearly 90 percent of the piñon pines across millions acres in Colorado, Utah and Arizona. Researchers have reported little forest regeneration.
According to one study published in the journal Ecosphere in 2012, the piñon pines across New Mexico and Oklahoma were producing fewer seeds, with the biggest drop in production occurring in areas that warmed the most during the March to October growing season. Overall, average temperatures in the study areas had increased by about 2.3 degrees Fahrenheit in the past 40 years.
The semi-arid Southwest, where forests historically have experienced extreme conditions, is a global hotspot for climate impacts. Along with the piñon decline, other forest researchers have projected that 72 percent of the region's needleleaf evergreen forests could die by 2050, with nearly 100 percent mortality by 2100, due to warmer and drier conditions, according to a 2014 study published in the journal Nature Climate Change.
Some scientists have raised concern that the issue is being underestimated.
"We surmise that mortality vulnerability is being discounted in part due to difficulties in predicting threshold responses to extreme climate events," according to a comprehensive forest study published last year in the journal Ecosphere by leading forest and climate researchers. The research documented tree deaths due to hotter and more frequent droughts, as well as warming feedbacks from forest die-offs.
In the decades of warming ahead, "there are key climate change drivers we know with high confidence will drive forest deaths around the world," the researchers said.
Adapted from: https://insideclimatenews.org/news/29062016/coral-millions-trees-joining-list-climate-change-casualties-california
Principle 3g
Misconceptions about this Principle
The Misconception
Isn’t it true that animals and plants can adapt to changes in the climate?
The misconception goes something like this: Aren’t corals, trees, birds, mammals, and butterflies adapting well to the routine reality of changing climate? It seems like I still see the same plants and animals that I have always seen. I don’t see a sudden wave of extinctions.
The Science
The rate of climate change is so fast that most species are having trouble adapting to climate change and the impacts on many will be far-reaching and severe.
While a small percentage of species may be able to adapt to a changing climate, the science tells us that a large number of ancient mass extinction events have been strongly linked to global climate change. Because current climate change is so rapid, the way species typically adapt (for example by migrating) is, in most cases, simply not possible. Global change is too pervasive and occurring too rapidly. Read More…
Source: http://www.skepticalscience.com/global-cooling-mid-20th-century.htm
The Science
The rate of climate change is so fast that most species are having trouble adapting to climate change and the impacts on many will be far-reaching and severe.
While a small percentage of species may be able to adapt to a changing climate, the science tells us that a large number of ancient mass extinction events have been strongly linked to global climate change. Because current climate change is so rapid, the way species typically adapt (for example by migrating) is, in most cases, simply not possible. Global change is too pervasive and occurring too rapidly.
Global warming to date has certainly affected species’ geographical distributional ranges and the timing of breeding, migration, flowering, and so on. The most well known study to date, by a team from the UK, estimated that 18 and 35% of plant and animal species will be committed to extinction by 2050 due to climate change.
A large number of ancient mass extinction events have been strongly linked to global climate change, including the most sweeping die-off that ended the Palaeozoic Era and the Palaeocene–Eocene Thermal Maximum, 55 million years ago.
There are a number of reasons why future impacts on biodiversity will be particularly severe:
A. Human-induced warming is already rapid and is expected to further accelerate.
B. A low-range optimistic estimate of 2°C of 21st century warming will shift the Earth’s global mean surface temperature into conditions which have not existed for 3 million years. More than 4°C of atmospheric heating will take the planet’s climate back, within a century, to the largely ice-free world that existed prior to about 35 million years ago.
C. Most habitats are already degraded and their populations depleted, to a lesser or greater extent, by past human activities.
D. Past adaptation to climate change by species was mainly through shifting their geographic range to higher or lower latitudes or up and down mountain slopes. Now, because of points A to C described above, this type of adaptation will, in most cases, simply not be possible or will be inadequate to cope. Global change is simply too pervasive and occurring too rapidly.
Principle 3
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.