Executive Summary

Main Points

• The Arctic is extremely vulnerable to projected climate change and its impacts. Over the period of this assessment, climate change is expected to contribute to major physical, ecological, sociological, and economic changes already begun in the Arctic. Because of a variety of positive feedback mechanisms, the Arctic is likely to respond to climate change rapidly and more severely than any other area on earth. The most direct and pronounced changes to the Arctic are likely to include changes in temperature and precipitation, with subsequent effects on sea ice and permafrost. Much smaller changes are likely for the Antarctic over the period of this assessment. The Antarctic is likely to respond relatively slowly to climate change.
• Substantial loss of sea ice is expected in the Arctic Ocean. If there is more open water, there will be impacts on the climate system of northern countries as temperatures moderate and precipitation increases. If 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 should increase biological production but may lead to different species composition on land and in the sea. On land, there will be a tendency for poleward shifts in major biomes and associated animals. However, the Arctic Ocean geographically limits movement of the tundra, taiga, and boreal forest. In the sea, marine ecosystems will move poleward. Animals dependent on ice may be disadvantaged.
• Changes in the polar climate are likely to affect the rest of the world through increased sea levels from melting of the cryosphere, increased warming of lower latitudes from slowing of oceanic transport of heat, and increased greenhouse gas levels through carbon dioxide and methane emissions in the Arctic.
• Human communities in the Arctic will be affected by these physical and ecological changes. The effects will be particularly important for indigenous peoples leading traditional lifestyles.
• There will be economic benefits and costs. Benefits include new opportunities for shipping across the Arctic Ocean, lower operational costs for the oil and gas industry, lower heating costs, and easier access for tourism. Increased costs can be expected from several sources, including disruptions caused by thawing of permafrost and reduced transportation capabilities across frozen ground and water. Sea-ice changes in the Arctic have major strategic implications for trade and defense.

Document Summary

• Regional Climate. Cold is the overwhelming characteristic of polar regions, with nine months of snow, ice, cold, and relative darkness. In the Arctic, there are only a few weeks of thaw, when much of the ground is boggy and awash with water. There also are episodes of extreme cold and storms. In Antarctica, temperatures mostly remain below freezing.
• Climate Trends. Parts of the Arctic and Antarctic have warmed over the past half-century, while some parts appear to have cooled. Precipitation seems higher. Trends in the overall ice balance of the world's major ice sheets in Greenland and Antarctica are uncertain. There is conflicting information on changes in the thickness and extent of sea ice globally. Ice seems to be thinning in the Arctic but not in the Antarctic.
• Vulnerability and Impacts. Systems in the Arctic and Antarctic Peninsula are extremely sensitive to temperature. The primary impacts will be on the physical environment, biota and ecosystems, and human activities. The Arctic Ocean has strong sensitivity to temperature because its exposed areal extent grows and shrinks by as much as 50% within a single year. Interannual variability in sea ice similarly shows extreme sensitivity to temperature. The Arctic terrestrial system, primarily based on permafrost, also is very sensitive to temperature because much of the permafrost is currently discontinuous. Strong positive feedback mechanisms within the Arctic suggest that climate change is likely to be more severe in the Arctic than in the rest of the world.
• Terrestrial Ecological Systems. Climate change may occur at a rapid rate relative to forest migration ability. If there is warming, there will be a poleward migration of the northern treeline. However, geographic limitations may restrict the migration of the boreal forest. If warming occurs and the forest cover changes, there will be major impacts on biological resources (e.g., bears, caribou, small mammals, amphibians, and insects). The effects of climate change have not been deeply investigated in the Antarctic terrestrial ecosystem, but its distribution and specific composition could be altered by global warming.
• Marine Ecological Systems. In general, productivity should rise. Warming should increase growth and development rates of nonmammals; however, ultraviolet-B (UV-B) radiation is still increasing, which may constrain primary productivity as well as fish productivity. Additional risks include the loss of sea-ice cover, upon which several marine mammals depend for food and protection. Also, Arctic shipping, oil exploration and transport, and economic development could bring risks to many species.
• Additional Stressors. In addition to climatically driven changes, such as changes in sea ice and temperature, the Arctic currently is stressed from a variety of sources, and some of these stresses are likely to increase in the next few decades. Additional stresses that may confound the effects of climate change include hydrocarbons, radionuclides, acidification, heavy metals, persistent organic pollutants, and UV radiation, as well as increased human development, traffic, and potential oil spills.
• Ice. If there is warming, the Arctic Ocean, as well as Arctic lakes and streams, could experience a thinner and reduced ice cover. In contrast, vast Antarctica is so cold that any warming within the IPCC scenarios should have little impact except in the Dry Valleys and on the Antarctic Peninsula. In fact, ice could accumulate through greater snowfall, slowing sea-level rise.
• Permafrost. Permafrost covers all of Antarctica and most of the Arctic. Much of the Arctic permafrost is close to thawing, making it an area extremely sensitive to even small changes in temperature. Effects of thawing permafrost include large-scale slumping, erosion, and sinking of areas. All of these effects will disrupt current vegetation, ecosystems, water balance, and human structures.
• Fisheries. Warming could lead to a rise in production unless changes in water properties would disrupt the spawning grounds of fish in high latitudes. There could be a substantial redistribution of important fish species. Fisheries on the margin of profitability could prosper or decline. Fishing seasons will lengthen, but most stocks already are fully exploited.
• Navigation and Transport. If sea-ice coverage is reduced, coastal and river navigation will increase. Opportunities for water transport, tourism, and trade will increase. The Arctic Ocean could become a major trade route. Seasonal transport across once-frozen land and rivers may become more difficult or costly. Offshore oil production should benefit from less ice.
• Sub-Antarctic Islands. These small, isolated, usually uninhabited islands in the Southern Ocean have specialized flora and important marine mammals and birds. Many seem to have warmed over the past 50 years, and this trend is expected to continue. Climate change impacts are unlikely to be important for most animal and bird species, but plant communities could change. Glaciers will probably shrink.
• Arctic Settlements. If the climate ameliorates, conditions will favor the northward spread of agriculture, forestry, and mining, with an expansion of population and settlements. More infrastructure-such as marine, road, rail, and air links-would be required. Changes in the distribution and abundance of sea and land animals will impact on traditional lifestyles of native communities.
• Infrastructure. If the permafrost thaws, much infrastructure-including pipelines, airstrips, water supply and sewage systems, building foundations, roads, rail lines, and mining systems and structures-will be damaged. Thawing could disrupt petroleum production in the tundra. Redesign and replacement of many of these systems will be needed.
• Integrated Analysis. Direct effects could include ecosystem shifts, sea- and river-ice loss, and permafrost thaw. Indirect effects could include positive feedback to the climate system. There will be new challenges and opportunities for shipping, the oil industry, fishing, mining, tourism, infrastructure, and the movement of populations, resulting in more interactions and changes in trade and strategic balance. There will be winners and losers. As examples, a reduced and thinning ice cover will disadvantage polar bears, while sea otters will have new habitats; communities on new shipping routes will grow, while those built on permafrost will have difficulties. Native communities will face profound changes impacting on traditional lifestyles.

IPCC Homepage