Polar Regions: Climate Change Impacts
Polar Regions: Climate Change Impacts
The polar regions are the areas surrounding the poles, the two points where Earth's axis of rotation passes through its surface. These regions are always oriented to the sun at a grazing angle, so they never receive strong overhead sunlight. Also, because Earth's axis is tilted with respect to the plane in which it circles the sun, for about half the year the poles receive weak 24-hour sunlight, and for the rest of the year are in constant darkness. As a result of these extreme conditions, the polar regions are the only areas on Earth where ice is found at low altitudes year-round. Since the poles are cold and the tropics are hot, air and water tend to circulate between them, transporting energy and driving Earth's weather and climate systems.
WORDS TO KNOW
ANAEROBIC: Lacking free molecular oxygen (O2). Anaerobic environments lack O2; anaerobic bacteria digest organic matter such as dead plants in anaerobic environments such as deep water and the digestive systems of cattle. Anaerobic digestion releases methane, a greenhouse gas.
EROSION: Processes (mechanical and chemical) responsible for the wearing away, loosening, and dissolving of materials of Earth's crust.
GREENHOUSE GAS: A gaseous component of the atmosphere contributing to the greenhouse effect. Greenhouse gases are transparent to certain wavelengths of the sun's radiant energy, allowing them to penetrate deep into the atmosphere or all the way into Earth's surface. Greenhouse gases and clouds prevent some infrared radiation from escaping, trapping the heat near Earth's surface where it warms the lower atmosphere. Alteration of this natural barrier of atmospheric gases can raise or lower the mean global temperature of Earth.
ICE CAP: Ice mass located over one of the poles of a planet not otherwise covered with ice. In our solar system, only Mars and Earth have polar ice caps. Earth's north polar ice cap has two parts, a skin of floating ice over the actual pole and the Greenland ice cap, which does not overlay the pole. Earth's south polar ice cap is the Antarctic ice sheet.
ICE CORE: A cylindrical section of ice removed from a glacier or an ice sheet in order to study climate patterns of the past. By performing chemical analyses on the air trapped in the ice, scientists can estimate the percentage of carbon dioxide and other trace gases in the atmosphere at that time.
ICE SHEET: Glacial ice that covers at least 19,500 square mi (50,000 square km) of land and that flows in all directions, covering and obscuring the landscape below it.
ICE SHELF: Section of an ice sheet that extends into the sea a considerable distance and that may be partially afloat.
PERMAFROST: Perennially frozen ground that occurs wherever the temperature remains below 32°F (0°C) for several years.
THERMOHALINE CIRCULATION: Large-scale circulation of the world ocean that exchanges warm, low-density surface waters with cooler, higher-density deep waters. Driven by differences in temperature and saltiness (halinity) as well as, to a lesser degree, winds and tides. Also termed meridional overturning circulation.
Global warming has had particularly strong effects on the polar regions, warming the northern polar region (the Arctic) at about twice the rate of the rest of the world. The situation in the south polar region (the Antarctic) is more complex, with the West Antarctic Peninsula seeing as much warming as the Arctic but the bulk of the continent seeing no warming. Warming is already having dramatic impacts in the Arctic, melting permafrost, shrinking summer sea-ice coverage to levels never recorded before, changing the lifestyles of Arctic peoples, threatening polar-bear populations, and accelerating the melting of the Greenland ice sheet. The latter has possible effects on ocean circulation patterns that shape climate worldwide, but especially in the Northern Hemisphere.
Historical Background and Scientific Foundations
The north polar region, the Arctic, has no clear geographic boundary but is usually defined as the surface on the globe from the North Pole southward to the Arctic Circle, that is, the line of 66° 33' north latitude, which slices through Alaska, Scandinavia, and the southern tip of Greenland as it circles the world. The central Arctic is overlain by the Arctic Ocean, which is covered by a relatively thin layer of floating sea ice, and surrounded by the northern coasts of Asia, Europe, North America, and Greenland. The only large, open connection that the Arctic Ocean has with the other oceans of the world is between Greenland and Europe in the North Atlantic, making that region a key link in the global system of ocean circulations. The largest mass of ice in the Arctic is the Greenland ice cap, which is 1 mi (1.6 km) thick on average and contains 954,000 cubic mi (3.9 million cubic km) of ice, about 10% of the ice on Earth— enough, were it all to melt, to raise sea level by at least 21 ft (6.5 m).
The south polar region, the Antarctic, is geographically quite different, with the continent of Antarctica centered on the pole and completely surrounded by the Antarctic ocean. All of Antarctica but the tip of its tail-like Western Peninsula is south of the Antarctic Circle, 66° 33' south latitude. Antarctica is 98% covered by an ice sheet that is 2.5 mi (4 km) thick on average and contains 7 million cubic mi (29 million cubic km) of ice, 90% of the ice on Earth (and 70% of its freshwater)— enough, were it all to melt, to raise sea level by about 200 ft (60 m).
Indigenous peoples such as the Eskimos have lived in lower-latitude Arctic areas for thousands of years, but never had any motive to undertake the arduous journey to the Pole itself or to explore the interior of the Greenland ice cap. No human beings visited Antarctica until the mid-nineteenth century, and there has never been an indigenous population on that continent. (Today, several hundred people occupy a number of scientific research stations on the continent, none permanently.)
In the twentieth and twenty-first centuries, the Greenland and Antarctic ice caps have played a central role in climate science, since their layered ice sheets— formed from hundreds of thousands of years of annual snowfalls, compressed into ice and buried under later years' snows—preserve samples of ancient air and, in the varying atomic weights of their oxygen atoms, a record of air temperatures at the times their water fell from the sky. Climate records for the Southern Hemisphere have been pushed back 800,000 years from the present by deep ice cores from Antarctica, with researchers hoping, as of early 2008, to obtain cores going back 1.5 million years. In Greenland, climate records from ice cores go back over 110,000 years.
Impacts and Issues
Both polar regions serve as heat sinks, that is, areas where more energy is radiated away from Earth than is absorbed. However, because the arrangement of land and sea at the two poles is so different—almost reversed—the two areas play distinct roles in global climate.
Because of the symmetrical arrangement of land and sea in the south polar region, water and air flow in well-defined circular patterns around Antarctica. This circumpolar vortex tends to isolate the interior of the continent from the atmospheric circulations of the rest of the world. Thus, most of the ice in Antarctica shows no signs of melting any time soon, and may even gain mass from increased snowfall. However, the West Antarctic Peninsula is not isolated by the circumpolar flow pattern and has warmed by about 5.4°F (3°C) over the last half century. As a result, 87% of the glaciers on the peninsula (about 300 of them) accelerated their flow to the sea by an average of 12% from 1993 to 2003, contributing to accelerating sea-level rise; further acceleration may have occurred since 2003.
In 2002, because of regional climate changes that have been traced to global climate change, the floating coastal Larsen B ice shelf (1,253 square mi, or 3,245 square km in area) collapsed unexpectedly in just one month. The breakup of the floating ice did not raise sea levels directly, but has allowed some glaciers on the West Antarctic Peninsula to accelerate further, which does raise sea levels.
The ice covering the North Pole, in contrast to that covering the South, can have no direct effect on sea level because it is already floating. However, it reflects most of the light that falls on it into space, keeping the north polar region (and thus Earth) cooler than it would be otherwise. It is fragile compared to Antarctica's ice or that of Greenland, being only a few meters thick and floating on water.
In 2007, unprecedented summer melting of the Arctic sea-ice cap was observed, with open water stretching from the Pacific to the Atlantic along the northern coast of North America for the first time in recorded history. Open sea absorbs more solar energy than ice, so the more the Arctic sea ice melts, the warmer the Arctic gets. Further, in 2006, measurements of the changing gravitational pull of ice in Greenland verified that the mass of the ice sheet is decreasing as glaciers (so far, mostly around the southern coasts) accelerate their flow to the North Atlantic. The freshwater from the glaciers may slow the overturning thermohaline circulation of the Atlantic Ocean, with effects on climate throughout the Northern Hemisphere.
Warming is already having other effects on the Arctic region. Melting of permafrost and speeded coastal erosion are damaging human settlements and forcing some villagers to flee to higher or more stable ground. Warmer conditions are causing shrubs and forests to spread forward and snow cover to form later in the fall, melt earlier in the spring, and cover less territory, all of which causes the land to be darker on average and to absorb more heat, speeding warming. Anaerobic decay of organic matter in melting permafrost may, in decades to come, release millions or billions of tons of methane, a potent greenhouse gas, further speeding global climate change. No other large ecosystem has been as severely impacted, as yet, as the Arctic. The West Antarctic Peninsula, although seeing dramatic warming, is almost devoid of life.
See Also Arctic Melting: Greenland Ice Cap; Arctic Melting: Polar Ice Cap; Glacier Retreat; Polar Ice.
Solomon, S., et al, eds. Climate Change 2007: The Physical Science Basis: Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. New York: Cambridge University Press, 2007.
Cazenave, Anny. “How Fast Are the Ice Sheets Melting?” Science 314 (2006): 1250-1252.
Dowdeswell, Julian A. “The Greenland Ice Sheet and Global Sea-Level Rise.” Science 311 (2006): 963-964.
Eilperin, Juliet. “Antarctic Ice Sheet Is Melting Rapidly.” Washington Post (March 3, 2006).
Schiermeier, Quirin. “The New Face of the Arctic.” Nature 446 (2007): 133-135.
Bach, Anne Dorte. “Climate Changes Are Linked Between Greenland and Antarctic.” Earth Observatory, U.S. National Aeronautics and Space Administration (NASA), November 9, 2006. <http://earthobservatory.nasa.gov/Newsroom/MediaAlerts/2006/2006110923604.html> (accessed December 3, 2007).
Handwerk, Brian. “Arctic Melting Fast: May Swamp U.S. Coasts by 2099.” National Geographic News, November 9, 2004. <http://news.national geographic.com/news/2004/11/1109_041109_ polar_ice_2.html> (accessed December 3, 2007).
“Larsen B Ice Shelf Collapses in Antarctica.” National Snow and Ice Data Center, March 18, 2002. <http://nsidc.org/iceshelves/larsenb2002> (accessed December 3, 2007).
“Mission News: NASA Finds Vast Regions of West Antarctica Melted in Recent Past.” U.S. National Aeronautics and Space Administration (NASA), May 15, 2007. <http://www.nasa.gov/vision/ earth/lookingatearth/arctic-20070515.html> (accessed December 3, 2007).