CROSSING A CLIMATE WATERSHED. Porcupine caribou herd migrates across the Kongakut River in the Arctic National Wildlife Refuge, Alaska. Like the Antarctic, the Arctic is now warmer than it has been in the past 400 years. This is consistent with most climate models, which predict disproportionate warming at the poles caused by higher levels of carbon dioxide and other greenhouse gasses in the atmosphere. Scientists are just beginning to see the effects of climate change on Arctic wildlife. A herd of Peary caribou in Northern Canada has been hard hit by deeper snow on winter feeding grounds, a predicted consequence of warmer winter temperatures and more open Arctic water. Increased snowfall in recent years also has made it more difficult for Alaskan caribou calves to survive.

BOREAL OVERVIEW. Meteorologist Scott Chambers of the University of Alaska installs a radiometer on a 50-foot meteorological tower above a black spruce forest near Fairbanks in May 1999. The boreal forest is the most extensive and possibly least studied of the world's forests, and is thought to be especially susceptible to climate change. Scientists suspect that regional tree lines will move north, forests will dry and burn more often, and insects will proliferate in a warmer climate. This is one of many towers installed in Alaska for baseline data to spot and predict changes in the forest-atmosphere relationship.

DYING FORESTS. About 3 million acres of mature white spruce forest on the Kenai Peninsula have been killed by a growing population of spruce bark beetles (Dendroctonus rufipennis) during the past few years. Scientists attribute the beetle infestation to rising average temperatures in South-Central Alaska, especially in winter. More beetle larvae can survive, and higher summer temperatures allow the insects to mature faster and spread more widely. The trees, which previously lived in balance with the beetles, do not have enough natural defenses against this assault.

NOT-SO PERMAFROST. Geophysicist Tom Osterkamp indicates ground level when he installed this temperature probe pipe near Denali Park; the contrast with the current level demonstrates that the permafrost has been thawing during the last 15 years. Alaska permafrost temperature has increased 0.5 (degrees) to 1.5 (degrees) C since 1980, which is when Osterkamp began measuring ground temperature at 30 sites. Many of those sites show thermokarsting (a sinking plot of ground caused by thawing permafrost) as the ice surface thaws. Serious effects include forest damage, sinking roads and buildings, eroding tundra riverbanks, changes in tundra vegetation, and -- perhaps most critical -- increased carbon dioxide and methane emissions from thawed peat.

EARTH CRACKS. The shoulder of a road cracks due to permafrost thaws in Fairbanks, Alaska.

THE POINT OF THE RESEARCH. Research assistant Lorraine Ahlquist inventories a plot of tundra at Toolik Lake, Alaska, for a long-term confirmation study of general circulation model predictions of global warming. Each meter plot is monitored by counting, measuring, and identifying each plant at 64 pointframe grids. Thus far, results indicate that warming and early snow melt increase plant leaf area, photosynthesis rate, and growth of sedges. Several international studies are monitoring similar tundra plots across the Arctic.

NEIGHBORHOOD EFFECTS. Crooked houses settling as permafrost thaws near the University of Alaska.

SEA LEVEL RISING.In the Arctic, sea level rise frequently combines with permafrost thaw to create severe erosion. The native village of Shismaref, Alaska, a village of about 590 Inupiats, perches on a sandy barrier island on the NW shore of Seward Peninsula. The rising Bering Sea has intensified shore erosion of the narrow spit since the 1950s; protective armor and wire gabions have been ineffective. The townspeople now are confronted with decisions surrounding the possible forced move inland, away from this traditional site.

ADVANCING A TREELINE HYPOTHESIS. New growth of black spruce on a hillside in Denali National Park headquarters; here, botanist Glenn Juday has found that forest cover has advanced to the highest elevations ever reached in the last century. This is consistent with the hypothesis that forest area has increased during a 150-year warming trend that features a substantial annual average temperature rise of 1.3 (degree) C since 1976. Although there is room in the southern tundra for forest expansion, the implications for boreal forest health and for the future of tundra wildlife and atmosphere interactions are unknown.