While the most direct climate threats are to the ice-dependent species of the Arctic, global warming is already having a major impact on tundra ecosystems. Permafrost (continuously frozen ground) is being lost throughout the southern regions of the Arctic, causing dry habitats to convert to bogs. Other major changes in vegetation are being recorded too. The tree line that marks the boundary of the Arctic has already moved 10 km northwards, the southern edges of the tundra are becoming shrubbier, spring is arriving earlier and the growing season is longer. Pests and diseases are likely to increase with warming. Alaska has experienced massive outbreaks of spruce bark beetle that have killed millions of trees, and spruce budworm is moving north too.
In the winter, caribou dig through snow to find lichens to eat. When there is freezing rain instead of snow (as predicted to occur more frequently under global warming scenarios) there can be large scale die-offs. In the spring, caribou switch to eating the fresh growth of tundra plants such as sedges and willows and follow the natural cue of increasing day length to start their migrations to the calving grounds. But now spring is coming earlier in the year, some caribou herds are reaching their breeding areas too late to take advantage of the best new plant growth, which is triggered by increasing temperature, not day length. There is recent evidence from West Greenland that fewer caribou calves are being born and less are surviving because the pregnant females are arriving at the breeding areas too late in the spring.
There are fears that similar mismatches of migration timing and peak food availability as well as loss of suitable tundra habitat could also negatively affect some of the many species of shorebird that breed in the Arctic, for example the sanderling, red knot, curlew sandpiper and golden plover. Read more on
Arctic wildlife and biodiversity.
