Observed impacts of climate change
Regional changes in climate, particularly increases in temperature, have already had discernible impacts on many physical and biological systems in many parts of the world. The evidence includes decrease in mountain glacier extent and ice mass in most glaciers globally, later freezing and earlier break-up of ice on rivers and lakes, lengthening of mid- and high-latitude growing seasons, poleward and altitudinal shifts of plant and animal populations, declines of some plant and animal populations, and earlier flowering of trees, emergence of insects and egg-laying in birds.
In the Arctic, observed changes include: generally warmer air temperatures, diminishing of snow and sea ice extent and duration,and thawing of permafrost. In some regions cooling has also occurred but the overall trend is a substantial warming over the last few decades, and in some areas precipitation has also increased.
Some projected future impacts globally:
- In the Arctic, a 21st century decrease in sea-ice extent up to 100% in summer, a widespread decrease in snow-cover extent, particularly in spring and autumn, permafrost degradation over 10 to 20% of the present permafrost area and a movement of the permafrost boundary northward by several hundred kilometers. Changes in the Arctic are expected to be much greater than in the middle and lower latitudes.
- Agriculture: Crop yields and irrigation demand could change. Probably the most affected would be people relying on isolated agricultural systems and living in arid and semi-arid regions
- Forests: Forests may undergo major changes and species composition of and geographical ranges of forests will change, risk of forest fires increases.
- Water resources: Changes in water supply and quality. Freshwater systems in the Arctic will also be affected due to changes in river runoff, including the timing of runoff from thawing permafrost, and changes in river and lake-ice regimes
- Coastal areas: Erosion of beaches, inundation of coastal lands, additional costs to protect coastal communities
- Species and natural areas: Risk of loss of habitat and species. Some arctic species, especially those that are adapted to the cold arctic environment are especially at risk of loss in general or displacement from their present locations.
- Cryosphere: Diminishing glaciers, Arctic ice