Adapted from: Global Climate Impacts in the United States. T.R. Karl, J.M. Mellilo, and T.C. Peterson (eds.). Cambridge University Press, 2009. Available online at USGCRP Regional Climate Change Impacts
Alaska has warmed at more than twice the rate of the rest of the United States over the past 50 years, with many consequences. Its annual average temperature has increased 3.4 degrees Fahrenheit, while winters have warmed by 6.3 degrees Fahrenheit. The higher temperatures are already causing earlier spring snowmelt, reduced sea ice, widespread glacier retreat, and permafrost warming.
The observed changes are consistent with climate model projections of greater warming over Alaska, especially in winter, as compared to the rest of the country. Climate models also project increased precipitation over Alaska. Simultaneous increases in evaporation due to higher air temperatures, however, are expected to lead to drier conditions overall, with reduced soil moisture. Average annual temperatures are projected to rise between 5 and 13 degrees Fahrenheit by late this century, with lower emissions of greenhouse gases yielding increases at the lower end of this range and higher emissions yielding increases near the high end of the range.
Key issues for Alaska include:
- Longer summers and higher temperatures are causing drier conditions. Between 1970 and 2000, the snow-free season increased by about 10 days across Alaska, primarily due to earlier snowmelt in the spring. A longer growing season has potential benefits, such as a longer season for summer tourism and agriculture. However, the white spruce forests in Alaska’s interior are experiencing declining growth due to drought stress, and continued warming could lead to widespread death of trees. Agriculture might not benefit from the longer growing season if soil moisture decreases.
- Insect outbreaks and wildfires are increasing with warming. During the 1990s, south-central Alaska experienced the largest outbreak of spruce beetles in the world as rising temperatures allowed the beetle to survive the winter and to complete its life cycle in half the usual time. Drought-stressed trees were unable to fight off the infestation. Fires in forests and other wildlands are also increasing. By the end of this century, the area burned in Alaska is projected to triple under a moderate greenhouse gas emissions scenario and to quadruple under a higher emissions scenario.
- Lakes are declining in area. Across the southern two-thirds of Alaska, the area of closed-basin lakes has decreased over the past 50 years. The greater evaporation and thawing of permafrost that result from warming is the likely cause of the decrease in closed-basin lakes, which are lakes without stream inputs or outputs. These lake and wetland areas provide breeding habitat for millions of waterfowl and shorebirds and are important hunting and fishing grounds for Native People. A continued decline in the area of surface water would present challenges for ecosystems and the people who depend upon them.
- Thawing permafrost is damaging roads, runways, and other infrastructure. As permafrost thaws, the land can sink and collapse, damaging forests, homes, roads, and other infrastructure. Economists estimate that thawing permafrost will add billions of dollars in repair costs to public infrastructure. Costs to private property have not yet been estimated.
- Coastal storms increase risks to villages and fishing fleets. The rate of erosion along Alaska’s northeastern coastline has doubled over the past 50 years. Alaska’s widespread coastlines are increasingly threatened by erosion from causes related to warming climate. They are losing their protective sea ice buffer, facing increased storm activity, and facing a thawing of coastal permafrost. As a result, the ground beneath some communities is literally crumbling into the sea.
- Displacement of marine species will affect key fisheries. Climate change is altering marine ecosystems in ways that affect commercial fisheries. Most of the nation’s salmon, crab, halibut, and herring come from Alaska. The world’s largest single fishery is the Bering Sea pollock fishery, which has undergone major declines in recent years. Air and sea temperatures have increased, and sea ice has declined in this region. Loss of sea ice changes the composition of plankton and other species, with significant repercussions for fisheries.
Adapted by Melanie Lenart, University of Arizona