Big thaw coming: climate change may slam Arctic.

If the changes in climate predicted for this century come to pass, everyone will be affected, but the people and creatures of the Arctic will face some of largest challenges.

Many arctic locales are already feeling the heat. Between 1943 and 2002, average annual temperatures in coastal regions north of 50[degrees]N--the latitude of Prague, Czech Republic, and Winnipeg, Manitoba-increased by 0.4[degrees]C, says John E. Walsh of the University of Alaska in Fairbanks. Average temperatures in the inland regions of those high latitudes jumped an average of 0.8[degrees]C. Some spots have seen even steeper rises: Average annual temperatures along the northern coast of Alaska have risen a full 2[degrees]C since 1973, Walsh notes.

Even modest projections of future climate change suggest that those trends will accelerate. Walsh and his colleagues used five global-climate models to assess the effects of the so-called B2 climate scenario developed by the United Nations' Intergovernmental Panel on Climate Change. In this moderate scenario, world population rises from 6.4 billion today to 10.4 billion by 2100 and atmospheric concentrations of greenhouse gases climb to only about twice their 1990 levels.

The five climate models suggest that at latitudes above 60[degrees]N--about that of Oslo, Norway, and Seward, Alaska--average annual temperatures will increase over the next century somewhere between 3.6[degrees]C and 5.5[degrees]C. Temperatures in some areas of northeastern Siberia would rise 8[degrees]C. Walsh presented the team's analyses last week in Montreal at a joint meeting of the American and the Canadian Geophysical Unions.

The models also indicate that warming trends will be most pronounced in winter months, a pattern that could dramatically affect the extent, thickness, and persistence of sea ice in the Arctic Ocean.

Higher temperatures would drive the 0[degrees]C isotherm--the geographic line along which the average annual temperature matches the freezing point of water--northward about 300 kilometers by 2100, thereby melting vast regions of permafrost. Many of the Arctic's highways, buildings, and pipelines rest on the currently firm but increasingly threatened foundation of soil now frozen year-round.

Biological effects of the expected warming at high latitudes will probably be extensive, says Fred J. Wrona of the University of Victoria in British Columbia. For example, migration routes of species that live or pass through the region could be altered, and creatures could be exposed to diseases that now afflict their relatives in more-temperate climates.

Most species that inhabit arctic freshwater lakes have adapted to harsh conditions that now provide ecological barriers to other creatures, says Wrona. Warmer temperatures would result in fewer days of ice cover on some lakes, increasing their biological productivity and making conditions conducive to species traditionally found at more-southerly latitudes.

Analyses of the long-term effects of warming in northerly regions are being compiled by a multinational group of scientists headquartered at the University of Alaska in Fairbanks. Later this year, that group will issue a comprehensive report that addresses the effect of the expected warming on phenomena such as river flow, species extinctions, human health, and land and water use among indigenous peoples.