Alaska includes a wide range of physical, climatic, and ecological diversity in its rain forests; mountain glaciers; boreal spruce forest; and expansive tundra, peat lands, and meadows. It contains 75 percent by area of the U.S. national parks and 90 percent of wildlife refuges, 63 percent of wetlands, and more glaciers and active volcanoes than all other states combined. There is not much pressure put on the land by humans, but the pressure put on its marine environment from large commercial fisheries is substantial.

Alaska has warmed substantially over the 20th century, especially over the past few decades. Average warming since the 1950s has been 4°F (2°C). The greatest area of warming—approximately 7°F (4°C)— has occurred in the interior of the state during the winter. The growing season has lengthened by more than 14 days since the 1950s. Precipitation has increased about 30 percent since 1968. The observed warming is part of a larger trend through most of the Arctic, which has been corroborated by many independent observations and measurements of sea ice, glaciers, permafrost, vegetation, and snow cover. The most severe environmental stresses in Alaska at present are climate related.

Two models run by the U.S. Global Change Research Program (the Hadley and Canadian models) indicate that as global warming progresses, temperatures will warm 1.5-5°F (1-3°C) by 2030, and 5-12°F (3-6.5°C) (Hadley model) or 7-18°F (4-10°C) (Canadian model) by 2100. The greatest amount of warming is expected to occur in the north during the winter. The models also project precipitation increases in most of the state, reaching 25 percent in the north and northwest, with areas of up to 10 percent decrease along the southern coast. The area is also expected to experience increased evaporation from the warming, which will offset the effects from the increase in precipitation, making the soils drier throughout most of the state.

The key issues stemming from global warming in Alaska will be the thawing of permafrost and the melting of sea ice. Permafrost underlies most of Alaska, and the recent several decades of warming have been accompanied by extensive thawing, causing increased erosion, landslides, sinking of the ground surface, as well as disruption and damage to forests, buildings, and infrastructure. Thawing is projected to accelerate under future warming, with as much as the top 30-35 feet (10 m) of discontinuous permafrost thawing by 2100.

Sea ice off the Alaskan coast is retreating and thinning, with widespread effects on marine ecosystems, coastal climate, and human settlements. Arctic sea ice has decreased 14 percent since 1978, the majority of it melted since the 1990s. Since the 1960s, sea ice over large areas of the Arctic basin has thinned by 3-6 feet (1-2 m), losing about 40 percent of its total thickness. All climate models project large continued loss of sea ice, with year-round ice disappearing completely (in the Canadian model) by 2100. The retreat of sea ice allows larger storm surges to develop, increasing the risk of inundation and increasing erosion on coasts that are also made vulnerable by permafrost thawing. In some regions, shorelines have retreated more than 1,500 feet (400 m) due to erosion over the past few decades. Several Alaskan coastal villages will soon have to be reinforced or relocated before they are destroyed. Loss of sea ice also causes large-scale changes in marine ecosystems, threatening populations of marine mammals and polar bears that depend on the ice for hunting and other activities.

The Gulf of Alaska and Bering Sea support diverse marine ecosystems and represent the nation's largest commercial fishery. Their productivity fluctuates with year-to-year and decade-to-decade climate variability. As global warming progresses, the variability is expected to continue. As fish populations decline, it will have a negative effect on the other animals that feed off them in the food chain.

There will also be increased stress on the subsistence livelihoods in the area. Many native people live in isolated rural communities where subsistence is practiced to gather food. In fact, Alaska's 117,000 rural residents collect about 43 million pounds (20 million kg) of wild food annually, equivalent to 375 pounds (170 kg) per person each year. Fish play a large role in their subsistence diet. Present climate change already poses serious harm to subsistence livelihoods. Reduced snow cover, a shorter river ice season, and thawing of permafrost all obstruct travel to harvest wild food. The retreat and thinning of sea ice, with associated stress on marine mammal and polar bear populations and increased open-water roughness, have made hunting more difficult, more dangerous, and less productive. In the long term, projected ecosystem shifts are likely to displace or change the resources available for subsistence, requiring communities to change their practices or move. Shifts in the composition of tundra vegetation may decrease nutrition available for caribou and reindeer. In addition, the invasion of the tundra by boreal or mixed forest will probably limit the range of caribou and musk ox.

As this chapter has pointed out, global warming is already having an effect on daily life worldwide, but when temperatures rise a few degrees, the current inconveniences could give way to dangerous conditions and even death. There is no safe haven from global warming—it is a global phenomenon. Given what scientists already know about global warming and its effects on the environment, it is not to early to begin taking mitigation and adaptation measures to deal with the challenges right now. It is critical to continue climate-impact research at local, regional, national, and global scales and consider the full range of stresses that can affect an ecosystem, such as climate change and variability, land use change, air and water pollution, and many other human and natural impacts. In order to achieve the most comprehensive results, scientists worldwide representing multiple scientific disciplines—such as those in the IPCC—need to continue to work together to solve the problem of global warming.

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