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Polar Regions
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 Introduction | Sea Ice | Wildlife | Forests
IntroductionPolar regions such as Alaska, the Arctic, and Antarctica contain a wide variety of physical features and ecosystems. The alpine and lowland glaciers, ice caps, sea ice, permafrost, boreal (see glossary) forests, tundra, peatlands, and meadows found in high-latitude regions are sensitive to subtle variations in air temperature, ocean temperature, and other climatic conditions.
Climate models indicate that global warming will be felt most acutely at high latitudes, especially in the Arctic where reductions in sea ice and snow cover are expected to lead to the greatest relative temperature increases. Ice and snow cool the climate by reflecting solar energy back to space, so a reduction in their extent would lead to greater warming in the region.
Many changes already are apparent in high-latitude regions. For example:
- Arctic temperatures during the late 20th century appear to have been the warmest in 400 years.
- Satellite data suggest that the extent of snow cover has declined by 10 percent since the late 1960s.
- During the 20th century, the annual duration of lake and river ice cover in the mid- and high latitudes of the northern hemisphere declined by about two weeks.
- Since the 1950s, the extent of northern hemisphere spring and summer sea-ice decreased by about 10 to 15 percent, and researchers have measured a decline of roughly 40 percent in the thickness of Arctic sea-ice during late summer and early autumn during the past several decades.
- Since the 1950s, Alaska has warmed by an average of 4 degrees Fahrenheit.
- Pine Island Glacier, part of the West Antarctic Ice Sheet, thinned by up to 1.6 meters (5.2 feet) per year between 1992 and 1999.
Trend in Northern Hemisphere snow cover derived from satellite data, 1978-1998.
Source: National Snow and Ice Data Center
Sea IceSea ice regulates exchanges of heat, moisture, and salinity in the polar ocean, and provides key habitat for wildlife.
A loss of sea ice leaves coasts more vulnerable to storm surges and erosion and alters the habitat of marine mammals such as polar bears, ring seals, and beluga whales, possibly affecting their population numbers or distribution.
Satellite data indicate record reductions in regional sea ice cover in recent years. Climate models project large continued losses of sea ice in the future.
Satellite-derived departures from monthly means in sea ice extent for the Northern Hemisphere, 1978-1998.
Source: National Snow and Ice Data Center
WildlifeResearchers reported in 1999 that a decline in the health of polar bears during the past two decades may be linked to rising spring temperatures in Hudson Bay and the early breakup of sea ice. Scientists from the Canadian Wildlife Service determined that polar bears' health may be declining from improper nutrition. Polar bears hunt one of their primary food sources, ringed seals, in the spring months on the sea ice. During the past 20 years, warmer temperatures have led the ice to break up about three weeks earlier in the season. This early breakup leaves less time for the bears to hunt seals and therefore means that they have less food.
Antarctic wildlife also has been affected by climate change, according to William Fraser of Montana State University. Fraser has documented significant declines-approximately 50 percent over the past 25 years-in populations of Adelie penguins near Palmer Station on the Antarctic Peninsula. The declines appear to be caused by regional changes in sea ice and snowfall, which in turn may be related to global climate change.
Forests
| Area near Ayiyak River in Alaska. Top image from 1949, bottom 2000. Shows increase in shrub patch density, individual shrub growth and shrub expansion into previously shub-free areas. Sturm, M., C. Racine, and K. Tape, 2001: Increasing shrub abundance in the Arctic, Nature, Vol. 411, p. 546-547. |
Changes in temperature and moisture are expected to have variable impacts on the forests of the high-latitude zones. Northern treelines are likely to advance slowly into areas now occupied by tundra. Forests whose productivity is not limited by the availability of moisture may become more productive as the climate warms, but this may be counterbalanced in some areas by increases in the frequency of fires and pest outbreaks.
Forests that are sensitive to drought may be adversely affected by global warming. For example, white spruce forests in interior Alaska have experienced severe stress from temperature-induced drought during the past 90 years.
Some Alaskan forests have experienced a sustained infestation of spruce bark beetles since 1992. The outbreaks, formerly limited by the cold, have caused the death of 2.3 million acres of trees on the Kenai Peninsula in Alaska. This is the largest loss of trees to insects ever recorded in North America.
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