Ecosystems: Major physical and ecological changes are expected in the Arctic. Frozen areas close to the freezing point will thaw and undergo substantial changes with warming. Substantial loss of sea ice is expected in the Arctic Ocean. As warming occurs, there will be considerable thawing of permafrost, leading to changes in drainage, increased slumping, and altered landscapes over large areas. Polar warming probably will increase biological production but may lead to different species composition on land and in the sea. On land, there will be a tendency for polar shifts in major biomes such as tundra and boreal forest and associated animals, with significant impacts on species such as bear and caribou. However, the Arctic Ocean geographically limits northward movement. Much smaller changes are likely for the Antarctic, but there may be species shifts. In the sea, marine ecosystems will move poleward. Animals dependent on ice may be disadvantaged in both polar areas.

Hydrology and Water Resources: Increasing temperature will thaw permafrost and melt more snow and ice. There will be more running and standing water. Drainage systems in the Arctic are likely to change at the local scale. River and lake ice will break up earlier and freeze later.

Food and Fiber Production: Agriculture is severely limited by the harsh climate. Many limitations will remain in the future, though some small northern extension of farming into the Arctic may be possible. In general, marine ecological productivity should rise. Warming should increase growth and development rates of nonmammals; ultraviolet-B (UV-B) radiation is still increasing, however, which may adversely affect primary productivity as well as fish productivity.

Coastal Systems: As warming occurs, the Arctic could experience a thinner and reduced ice cover. Coastal and river navigation will increase, with new opportunities for water transport, tourism and trade. The Arctic Ocean could become a major global trade route. Reductions in ice will benefit offshore oil production. Increased erosion of Arctic shorelines is expected from a combination of rising sea level, permafrost thaw and increased wave action as a result of increased open water. Further breakup of ice shelves in the Antarctic peninsula is likely. Elsewhere in Antarctica, little change is expected in coastlines and probably in its large ice shelves.

Human Settlements: Human communities in the Arctic will be substantially affected by the projected physical and ecological changes. The effects will be particularly important for indige-nous peoples leading traditional lifestyles. There will be new opportunities for shipping, the oil industry, fishing, mining, tourism, and migration of people. Sea ice changes projected for the Arctic have major strategic implications for trade, especially between Asia and Europe.

Conclusions: The Antarctic peninsula and the Arctic are very vulnerable to projected climate change and its impacts. Although the number of people directly affected is relatively small, many native communities will face profound changes that impact on traditional lifestyles. Direct effects could include ecosystem shifts, sea- and river-ice loss and permafrost thaw. Indirect effects could include feedbacks to the climate system such as further releases of greenhouse gases, changes in ocean circulation drivers, and increased temperature and higher precipitation with loss of ice, which could affect climate and sea level globally. The interior of Antarctica is less vulnerable to climate change, because the temperature changes envisaged over the next century are likely to have little impact and very few people are involved. However, there are considerable uncertainties about the mass balance of the Antarctic ice sheets and the future behavior of the West Antarctic ice sheet (low probability of disintegration over the next century). Changes in either could affect sea level and Southern Hemisphere climates.