The first IPCC report, issued in 1991, discussed changes we could expect decades in the future. Some of those are happening now, as reported in the IPCC's 2007 assessments. Our confidence in projecting future changes has also improved.
Some of the trends now under way—such as warmer nights during heat waves and heavier bursts of rain and snow—are expected to continue. Other changes will be less familiar, and there could be surprises along the way. This increased uncertainty makes planning for the future more difficult.
Our ability to adapt is one of our greatest strengths as a species. But in this case, the medicine could feed the disease. As we adapt to climatic changes already happening, some of those behaviors will affect the amount of greenhouse gases we put into the atmosphere, and thus affect the climate itself. Population growth, increases or decreases in air pollution, increased ability to purchase air conditioning or automobiles, and other social and economic changes are difficult to pin down decades into the future. This is why IPCC climate scientists have created a number of emissions scenarios; each one sketches a different set of possible future social, economic, and technological developments for use in projecting future changes in the climate.
Here's a look at some of the impacts we're already experiencing and some of the research at NCAR and in the wider research community that's focusing on the connections between global warming and Earth's ecosystems.
Current environmental impacts and prospects for the future
Changes in weather
Heat and heat waves
Record-breaking heat across the United States during July 2006 is shown in red on this map from NOAA's National Climatic Data Center. Click here or on the map to open a NOAA Web page with details on the extreme heat. (Image courtesy NOAA.)
The IPCC reports that hot days, hot nights, and heat waves all have become more frequent globally in the last 50 years.
Europe’s 2003 heat wave, which resulted in more than 40,000 deaths, was the hottest in 150 years of modern record keeping, and possibly the hottest in 500 years, by some estimates. There is at least double the risk of such deadly heat waves ocurring in Europe compared to what it would be if we were not adding greenhouse gases to the atmosphere, according to a 2004 study in the journal Nature.
Sacramento, California, saw its warmest overnight low on record (84 °F, or 27°C) during a July 2006 heat wave that killed more than 100 people across the state. The city’s previous record for warmest low was 79°F (26°C). Many other western U.S. cities also saw their hottest day or night ever reported.
What can we expect?
By the 2040s, the average summer in Europe may be similar to the scorching one of 2003, according to the Nature study cited above.
A report by two NCAR scientists found that Chicago’s heat waves could become 25% more frequent by the 2080s. Nighttime lows during the worst heat waves in the U.S. South and West are projected to warm by more than 5°F (3°C).
On average, precipitation has increased globally over the last century, including over the United States.
Days with heavy rain and snow are becoming more frequent over most of the globe’s land areas, including North America, according to IPCC Working Group I.
Despite this, the global extent of drought has more than doubled worldwide since the 1970s, according to an NCAR study.
The more precipitation/more drought paradox is because
rising temperatures allow more water to evaporate from oceans (adding extra moisture to the air for rain or snow),
but that warming also draws moisture out of the ground, worsening drought wherever it’s not raining.
What can we expect?
By the 2080s, most land areas north of latitude 40°N, from Europe to the northern U.S. states and Canada, will see a jump in the number of days with precipitation greater than 0.40 inch (1 centimeter), according to NCAR research.
Another study found widespread agreement among computer models that the U.S. Southwest, from the southern Great Plains to California, may be entering a semipermanent state of drought, with "normal" years by the 2030s becoming as dry as the 1930s Dustbowl or the persistent drought of the 1950s.
The strongest U.S. tornadoes have not become more frequent in the last 50 years. Reports of weaker tornadoes are increasing as more people watch for them.
Based on data since the 1970s, the most intense hurricanes (those ranked Category 4 or higher on the Saffir-Simpson scale) make up an increasing fraction of tropical cyclones worldwide.
Sea-surface temperatures have increased in the parts of the Atlantic and Pacific where warm water fuels hurricanes over the last century. The warming is more likely due to human-produced climate change than natural cycles, according to research reported in June and September 2006.
What can we expect?
Research continues on the effects of climate change on tornadoes, severe thunderstorms, and hurricanes. The trends should become more clear as the length of observation records grows. Because extremes are by definition rare, it takes a long time to gather enough data to make definitive statements.
Computer models of the global climate cannot directly simulate tornadoes and other small-scale weather features. More progress will emerge as fine-scale models that depict hurricanes and severe storms are linked to global simulations, as with the Nested Regional Climate Model now being developed at NCAR.
Changes in ecosystems
Even gradual warming can have dramatic impacts on ecosystems. By crossing important thresholds, such as when freezing or thawing occur, small shifts in climate can transform the way plants, animals, and landforms interact.
The polar and mountainous regions of Earth are especially vulnerable to climate change. The huge amounts of snow and ice in cold regions act as natural air conditioners—not because they're frozen, but because their light-colored surfaces span vast areas, reflecting most of the sunlight that hits them. If the ice melts, the darker surface underneath (whether land or sea) absorbs much more of the sunlight, like asphalt paving does on a hot day. That helps to speed further warming and melting in what’s known as a positive feedback loop.
Many plants and animals survive within a narrow range of very specific climate conditions. As climate zones shift, some plants and animals are adapting, but others are less-well equipped to do so.
During recent summers, the ice that covers the Arctic Ocean has been retreating further than ever measured. The extent of Arctic ice in September 2006 was only about 80–85% of what it was in the 1980s and 1990s.
Many glaciers on the coasts of Greenland and West Antarctica are melting at an accelerating clip. When ice shelves and glacier tongues break away from the coast (as in the spectacular Larsen B collapse of 2002), it allows the ice upstream to flow more quickly toward the sea. A major chunk of Antarctica's Wilkins Ice Shelf collapsed in the spring of 2009 and is being monitored for further losses. For time lapse video of melting glaciers around the world, see the Extreme Ice Survey website.
Over frigid and desolate East Antarctica, the ice cover may be increasing as temperatures warm and snow becomes heavier. Ironically, this increased precipitation could also be related to global warming.
Permafrost (permanently frozen soil) is thawing in parts of Canada, Alaska, and Siberia. The impacts include building and road damage, sinkholes, and “drunken forests” in and near such cities as Fairbanks, Alaska, and Irkutsk, Russia. The thawing is destabilizing both modern and traditional ways of life in Arctic regions.
Glaciers are also retreating in midlatitude and tropical mountains such as the Andes, Himalayas, and Alps. Based on the available data, this appears to be mainly due to gradual warming, but in some cases—such as Mt. Kilimanjaro in Africa—reduced precipitation may be a more significant factor.
Summer sea ice in the Arctic could decrease dramatically by the 2020s, according to climate-model studies that also suggest virtually ice-free Arctic summers are possible by 2040. The ice loss threatens the survival of polar bears and other Arctic species.
The melting of ice from Greenland, West Antarctica, and glaciers elsewhere will add to sea-level rise, which could range from 7 to 24 inches by 2100 according to the IPCC’s most recent estimates. However, some aspects of melting that could speed glacial loss are not fully represented in models or in the IPCC’s own estimates because they remain poorly understood. An NCAR study in 2006 found that the Arctic’s summer warmth by 2100 could match that of 130,000 years ago, when sea levels were rising to 20 feet above today’s levels. Even if levels rise far less than that, a 2009 study suggests the coastal United States, and particularly the northeast from New York up through Canada, is especially vulnerable.
Most of the world’s permafrost could thaw by the end of this century, an NCAR study found in 2004.
Tropical and midlatitude glaciers will continue to retreat. Some projections show, for example, that the namesakes of Glacier National Park could be gone by 2030.
Huge swaths of forest in Canada, Alaska, and Russia have been ravaged over the last decade by forest fires, fed by record summer heat and drought. These fires add large amounts of carbon dioxide, which is also the major human-produced greenhouse gas, to the atmosphere. However, a 2006 study found that high-latitude fires may have an overall cooling effect in the long term, as snowfall on the newly exposed ground reflects winter sunlight for many years afterward.
As the climate warms, forests are also moving north into land that was once Arctic tundra. These trees will act to warm the climate by darkening the surface.
In some northern high latitudes, the growing season is up to two weeks longer than in the 1950s. Sakura, Japan's most common species of cherry blossom, now blooms five days earlier. Some plant species are moving northward in search of the cooler climate they need to reproduce.
Warmer winter nights and fewer cold snaps in New England have helped reduce yields of maple syrup. This climate-related decline is one of several factors involved in shifting syrup production from the United States to Canada over the last 40 to 50 years.
What can we expect?
Periods of high fire risk will continue to lengthen across northern forests, with large increases in the areas burned, according to the IPCC.
Planting trees is one suggested response to climate change, because trees absorb carbon dioxide, the most abundant greenhouse gas produced by human activity, as they grow. But new research shows that, depending on where they grow, some forests can intensify global warming, rather than easing it.
At higher latitudes, such as Canada and Russia, snow cover reflects sunlight back into space, which helps cool the region. But trees block the process and so contribute to warming.
In the tropics, forests catch rainfall and evaporate it back into the air, helping cool that region.
In midlatitudes, where the bulk of the United States is located, tree planting appears to have little overall effect on climate, even when the carbon absorption is taken into account.
Some animal species are already shifting toward higher elevations or higher latitudes, as warming intersects with other natural and human-produced environmental change. A landmark 2003 survey found that more than a third of 677 species examined had been affected by climate change, moving an average of 3.7 miles poleward per decade and/or 20 feet up in elevation. Pika, diminutive rodents found in mountainous parts of North America and Asia, have disappeared from more than half of their range in the U.S. Great Basin in the last century. A 2006 report based on 800 scientific studies concludes that many species cannot keep pace with climate change and face extinction.
Warmer ocean temperatures, most evident during El Niño events, have weakened or killed off coral species during "bleaching" incidents. More than 15% of the world’s reefs were damaged by ocean warming associated with the 1997–98 El Niño. Warming waters and related changes are also helping push some algae, plankton, and fish species poleward.
Another threat to coral reefs arises from changes in the chemistry of ocean water that make the water less alkaline as it absorbs carbon dioxide from the atmosphere. Scientists are investigating the potential harm to marine life from this process of ocean acidification.
A reduction in the intensity of winter cold snaps is expanding the range where some insects can flourish. Mountain pine beetles and spruce budworm have invaded forests across western North America. The U.S. range of fire ants has expanded each year since the 1960s by an area the size of New Hampshire.
More than 30% of amphibian species have been recognized as vulnerable, endangered, or critically endangered. There are multiple causes, including the interaction of warming temperatures with rainfall cycles and seasonality, as well as ozone depletion, pollution, and other environmentally induced stresses.
Bird species never before noted in the traditional knowledge of the Inuit people, such as robins and sparrows, are now being observed in the far north.
What can we expect?
Many species now stressed by climate change will continue to be affected. According to the IPCC, some 20–30% of plant and animal species assessed thus far are likely to be at increased risk of extinction if the global average temperature warms more than about 2.7–4.5°F (1.5–2.5°C), which may occur by later this century.
Temperature and precipitation change will influence the territory of mosquitoes and other disease-carrying insects. For some ailments, such as malaria, the areas of prevalence may expand in some regions and contract in others. Climate is one of many factors influencing insect-borne diseases. Scientists are working to better understand a variety of issues involving climate and health.
Coral reefs are expected to continue declining as ocean temperatures warm and ocean chemistry becomes less alkaline.
The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.