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Polar Regions
Related Links
NASA
- Arctic Sea Ice Observations
- Antarctic Climate Change
- NASA and NSF West Antarctic Ice Sheet Initiative
NOAA
Other 
Polar regions include the Arctic in the Northern Hemisphere and Antarctica in the Southern Hemisphere. The Arctic encompasses a large, mostly frozen ocean surrounded by land, is home to almost four million people (ACIA, 2004), and includes some or all of the territories of eight nations, including the United States. By contrast, Antarctica is an ice-covered continent surrounded by ocean and is generally uninhabited.
The Arctic is expected to experience the greatest rates of warming compared with other world regions (IPCC, 2007a). In part, this is because ice has greater reflectivity (also known as albedo) than the ocean or land. Melting of highly reflective snow and ice reveals darker land and ocean surfaces, increasing absorption of the sun's heat and further warming the planet, especially in those regions. There is evidence that climate change is already having observable impacts in the Arctic and in Antarctica. Many of these observed changes are consistent with the expected effects of climate change under a range of climate scenarios.
Arctic
Figure 1: Observed sea ice changes. This animation shows sea ice coverage shrinking from 1979 to 2005, by roughly half. Source: NASA
In 2004, the Arctic Climate Impact Assessment
(ACIA) was
released. This report was produced by an international team of scientists
at the
request of the
Arctic Council ,
an 8-nation intergovernmental forum including the United States. The
ACIA concluded
the following:
Effects on the Climate System
- Average temperatures in the Arctic have risen at almost twice the rate as temperatures in the rest of the world over the past few decades.
- Widespread melting of glaciers and sea ice and rising permafrost temperatures present additional evidence of strong Arctic warming (see Figure 1).
- The above trends are expected to continue during this century, resulting from ongoing increases in atmospheric concentrations of greenhouse gases (though greenhouse gases do not primarily originate from the Arctic).
- Melting of Arctic glaciers is a contributing factor to sea-level rise around the world.
- Warming is very likely to alter the release and uptake of greenhouse gases from soils, vegetation, and coastal oceans.
- Reduction in sea ice is very likely to have devastating consequences for polar bears, ice-dependent seals, and local people for whom these animals are a primary food source.
Effects on Biological and Human Systems
- Arctic impacts will have implications for biodiversity around the world because migratory species depend on breeding and feeding grounds in the Arctic.
- Reduced sea ice is likely to increase marine access to the region’s resources, expanding opportunities for shipping and possibly for offshore oil extraction (although operations could be hampered initially by increasing movement of sea ice in some areas).
- As frozen ground thaws, many existing buildings, roads, pipelines, airports, and industrial facilities are likely to be destabilized.
- Increased areas of tree growth in the Arctic could serve to take up carbon dioxide (CO2, the principal greenhouse gas emitted by human activities) and supply more wood products and related employment, providing local and global benefits. However, tree growth would mean absorption of additional sunlight (as the land surface would become darker and less reflective) and add to regional warming.
- Climate change is taking place within the context of many other ongoing changes in the Arctic, including observed increases in chemical contaminants entering the Arctic from other regions, overfishing, land use changes that result in habitat destruction and fragmentation, rapid growth in the human population, and cultural, governance and economic changes.
The conclusions of the ACIA report are further supported by evidence from remote sensing technologies. Satellites and U.S. and British Navy submarines have provided data on retreating Arctic sea ice and decreasing Arctic ice thickness. Satellite data show that the extent of Arctic sea ice has decreased by about three percent per decade. Figure 2 below shows trends in Arctic sea ice extent since the 1860s.
Figure 2: Long-term trends in Northern Hemisphere sea ice extent for March and September, Nordic sea ice extent for April, and Russian Arctic sea ice extent anomaly (compared with the mean for the entire period) for August. Source: IPCC, 2007a
Upward-looking sonar data from U.S. Navy submarines between 1987 and 1997 show it is very likely that average ice thickness in the Arctic has decreased by up to 1 meter (IPCC, 2007a).
The Intergovernmental Panel on Climate Change (IPCC 2007a and 2007b) supports and extends the ACIA’s conclusions with additional evidence. The IPCC notes that “the resilience shown historically by Arctic Indigenous Peoples is now being severely tested,” with impacts on food availability and personal safety that are changing hunting and traveling practices. Community infrastructures will be harmed by the warming and thawing of permafrost. A less severe climate may bring benefits as well, such as reduced heating costs, new agricultural and forestry opportunities, and more navigable northern sea routes, but such benefits will depend on local conditions.
Antarctica
Like the Arctic in the Northern Hemisphere, Antarctica in the Southern Hemisphere has been experiencing effects attributable to changes in regional climate. Future changes resulting from global climate change are also expected to be significant in this region of the world.
Over the past half-century, there has been a marked warming trend in the Antarctic Peninsula. Much of the rest of Antarctica has cooled during the last 30 years, due to ozone depletion and other factors, but this trend is likely to reverse. Surface waters of the Southern Ocean surrounding Antarctica have warmed and become less saline, and precipitation in this region has increased (IPCC, 2007a).
Antarctica has experienced significant retreat and collapse of ice shelves, the result of regional warming. The loss of these ice shelves has few direct impacts on sea level and global climate. Because the ice shelves were floating, their melting does not directly add to sea level rise. They usually are replaced by sea-ice cover, so overall albedo (reflectivity) changes very little (IPCC, 2007a).
Satellite observations show no significant change in Antarctic sea-ice extent over the 1973-2005 period. Analysis of whaling records and modeling studies provide some evidence for longer-term declines in sea ice extent in some regions, but there are not enough data to provide firm conclusions (IPCC, 2007a).
As climate change continues, most of the land-based Antarctic ice sheet is actually likely to thicken if projected warming increases snowfall. There is a small risk, however, that the West Antarctic ice sheet will retreat in coming centuries. This is because the West Antarctic ice sheet is moored in an oceanic basin, where slippery mud covers the basin floor. This unique setting makes the ice sheet potentially unstable (IPCC, 2007a).
References
- Arctic Climate Impact Assessment (ACIA), 2004: Impacts of a Warming Arctic:
Arctic Climate Impact Assessment . Cambridge University Press, Cambridge,
United Kingdom and New York, NY, USA, 144 pp.
- IPCC, 2007a: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning (eds.)].
- IPCC, 2007b: Climate Change 2007: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Third Assessment Report of the Intergovernmental Panel on Climate Change [Parry, Martin L., Canziani, Osvaldo F., Palutikof, Jean P., van der Linden, Paul J., and Hanson, Clair E. (eds.)]. Cambridge University Press, Cambridge, United Kingdom, 1000 pp.