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Updated 12 October, 2003

US National Assessment of
the Potential Consequences
of Climate Variability and Change
Educational Resources
Regional Paper: Alaska


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Anchorage, Alaska

No other region of the United States is likely to be affected more by climate change than Alaska. In contrast to other regions and with the exception of direct fishing pressure on marine ecosystems, the most severe environmental stresses in Alaska are already climate-related. The amount of past temperature change, rate of climate warming, and projected changes in climate could pose some additional opportunities, as well as a range of problems, for Alaska's residents. Past and future changes in climate could have important international economic implications as well.

Alaska is about the size of one-fifth of the 48 contiguous states. This large area encompasses several distinct climatic and ecological regions. The southern coastal margin, including the panhandle and Aleutians, has a maritime climate with cool summers, relatively mild winters, and heavy precipitation, up to 200 inches annually in parts of the southeast, forming large glaciers on the southern mountains. North of the Alaska Range the climate is continental, with moderate summers (July average 59F), very cold winters (January average -13F), rapid seasonal transitions, and annual precipitation of 8-16 inches. The North Slope beyond the Brooks Range has an Arctic semi-arid climate, with annual precipitation less than 8 inches, average July temperature around 39F, and snow on the ground nine months of the year.

The normal low annual average temperatures in Alaska result in widespread areas of permafrost and extensive sea ice. Permafrost is a permanently frozen layer that can be found at varying depths under the surface of the Earth (under forests, under tundra, under houses) and is present in all of the state except a narrow belt along the southern coast. Recent warming has been accompanied by several decades of thawing in discontinuous permafrost, which is present in most of central and southern Alaska, causing increased ground subsidence (sinking), erosion, landslides, and disruption and damage to forests and other ecosystems, and buildings and other infrastructure. Sea ice, generally off the western and northern coasts of Alaska, is retreating (by 14% since 1978) and thinning (by 40% since the 1960s). The retreat and thinning of sea ice is having widespread effects on marine ecosystems, coastal climate, human settlements, and subsistence activities. Alaska is also strongly affected by El Niño (lasting about 1 year) and the interdecadal (lasting decades) Arctic Oscillation, bringing warmer and wetter winters to coastal Alaska in their warm phases, and cooler, drier winters in their cool phases

The El Niño Southern Oscillation (ENSO) Phenomenon

El Niño events occur when the trade winds that normally blow from east to west over the Pacific Ocean diminish and the waters of the central and eastern tropical Pacific become warmer than normal. There are two phases of ENSO. The term El Niño is used to refer to the warm phase and La Niña is used to refer to the cool phase. The ENSO cycle, normally about one year in length, is a continuously changing pattern of ocean-atmosphere behavior and is one of the dominant patterns of natural variability in the climate system worldwide. It often causes rainfall patterns and amounts to change in various locations around the globe, for example, during El Niño there is increased rainfall in the eastern Pacific, and drought conditions in Indonesia and Australia. Historically it has occurred approximately every 2-7 years.


Arctic Oscillation

The Arctic Oscillation (AO) is a hemispheric-scale seesaw of heat and mass between the Arctic region and Northern Hemisphere middle latitudes. The AO is characterized by related changes in westerly wind speed, temperature, and sea level pressure between the Arctic and the mid-latitudes all around the Earth. The AO is an especially important influence during the winter, being second only to the El Niño/Southern Oscillation in contributing to mid-latitude variations such as especially cold and dry or warm and wet winters. Over the Atlantic Ocean, the AO pattern closely resembles the North Atlantic Oscillation (NAO) (see the NE region for a discussion of the NAO).

The high phase of the AO is characterized by lower than normal sea level pressure and cooler than normal temperatures in the Arctic and by higher than normal westerly wind speeds and warmer than normal conditions in the mid-latitudes over the continents. The strong westerly winds carry warm oceanic air from the Atlantic to northern Europe and Asia causing a local warming. Also onshore winds from the Pacific Ocean warm North America. At the same time, colder continental air is flowing off the land and cooling the areas of the Bering Strait and Newfoundland. Conversely, the temperature gradient between the Arctic and the mid-latitudes is decreased during the low phase, leading to weaker westerly winds and cooler, drier winters.

Although a specific weather system may only have a lifetime of up to a few weeks, the prevalence of a particular type of weather pattern (so a phase of the AO) may be dominant for decades. Such dominance could result in, for example, long stretches of warmer or colder than normal winters in particular locations. The cause (or causes) of changes in the phases of the AO is not well understood, but may be naturally induced factors such as solar variations, and/or may be excited or changed in magnitude by human influences, such as from increasing greenhouse gas emissions or Arctic ozone depletion. The changes in temperature and winds associated with the AO take place not only at the surface, but extend upward from the surface to the stratosphere, thereby also affecting amounts of ozone, for example. Observations and modeling indicate that stratospheric changes may in turn play a significant role in forcing the AO into a particular phase.

Ecologically, Alaska is characterized by extremes ranging from cool temperate rainforests to boreal forests and Arctic tundra. Boreal forests are tree stands that live in areas just slightly warmer than the tundra. This state's vast forests include 114 million acres in the northern interior (Fairbanks) and a 12.5-million acre expanse of forest that runs along the state's rainy Pacific Coast (from Anchorage to Southeast Alaska). A mere 30,000 acres is devoted to agriculture, and an additional 185,000 acres serve as pastureland. Reindeer herds graze on 12 million acres, primarily on Seward Peninsula. Large parts of Alaska are set aside as wilderness areas, nature preserves, and national parks. Together these areas constitute nearly 80 percent of our entire nation's public lands. Alaska contains roughly 40% of the nation's surface water resources (lakes, rivers, streams), 63% of the wetlands, essentially all of the permafrost, and more glaciers and active volcanoes than all other states combined.

Direct human pressures on the state's land environment are light, but pressures on its marine environment from large commercial fisheries are substantial. Lightly populated, 614,000 people in 1998, and with a population growing about 1.5% per year, Alaska has the nation's highest median household income, and the economy is dominated by government and natural resources (including oil and gas, fisheries, forestry, and mining). Diverse subsistence livelihoods, practiced primarily by native communities (who comprise about 16% of the population), depend on fish, marine mammals, and other wildlife, and play a social and cultural role vastly greater than their monetary contribution.

Historical Climate Trends

Although observation records of climate change from the early part of this century are available for just a few Alaska locations, tree rings and other proxy indicators of climate change have supplemented instrument-based records to help reconstruct Alaska's climate trends well before the 20th century. That evidence has indicated that the Arctic is warmer in the 20th century than during any other time in the past 400 years.

Temperature & Precipitation Changes Measured Over the 20th Century

Climate records indicate that Alaska has experienced the largest regional warming of any state in the US. The state has warmed an average of 5˚F since the 1960s, with the largest warming of about 8˚F in the interior in winter. The Alaska regional warming is part of a larger warming trend throughout the Arctic region. Some regions in Alaska show a warming of nearly 3-4˚F quite suddenly in the late 1970s. As a result of the recent warming, the state's northern interior and its coastal forest region are now warmer than at any time in the last several centuries and very probably the last millennium. There has been extensive melting of glaciers, thawing of permafrost, and reduction of sea ice. The large observed warming has been accompanied by increasing precipitation. Alaska has become wetter, with a 30% average precipitation increase everywhere but the panhandle just between 1968 and 1990. Local weather records also show the growing season in Alaska has lengthened by more than 13 days since 1950.

Weather and Climate

Distinguishing clearly between the terms weather and climate is important to understanding how to interpret the results of this section. Weather is the hour-to-hour and day-to-day state of the atmosphere: whether, at a particular time, it is rainy or sunny, warm or cold, windy or calm. Climate is the average weather over time: a locale's typical weather patterns, including frequency and intensity of storms, cold outbreaks, and heat waves.

Just as the weather varies naturally, the climate varies naturally in response to such factors as sunspots, volcano eruptions, and atmosphere-ocean interactions (e.g., El Niño events). Climate change is a shift in the climate that lasts a few decades or more. Human activities in the last two centuries have become important drivers of climatic change. For this paper, whether the cause of an impact is natural or anthropogenic (human) is less important than whether it has to do with long-term trends or shorter patterns of variation. Thus we use more intuitive definitions: 1. variability refers to day-to-day, season-to-season, year-to-year, and decade-to-decade patterns of weather and climate; 2. climate change refers to longer-term trends in the average weather and climate, usually measured and experienced by long-term changes in temperature, precipitation, and sea level.

Global Warming or Climate Change

The media often uses the term global warming when talking about changes to the global climate. The phrase climate change, however, actually encompasses the more intricate set of changes that scientists are projecting. For example, the world is not expected to warm uniformly and some areas actually could become cooler as other parts of the Earth warm. Although more rain and snowfall are expected as the globe warms, some areas will become drier at the same time that other areas become wetter. The phrase climate change is, therefore, a more accurate way to describe projected changes to the global environment.

Possible Futures

Note about
General Circulation

Model results have projected that northern areas of the Northern Hemisphere will experience the most rapid and widespread warming on our planet principally because of the ice-albedo feedback. Ice-albedo feedback occurs because ice and snow are whiter than the land or water they cover, so after melting the exposed surface absorbs more radiation, accelerating further warming.

It is of concern that most models predict Alaska will continue to warm -- with the largest changes coming in winter months. Some models suggest increasing temperatures in the early part of the 21st century of anywhere between 1.5 -- 5 F and with 5 -- 18 F warming by 2100. The models used in this study also project by 2100 significant to complete loss of sea ice in the Arctic in the summer months. The models project Alaska getting wetter, with the biggest increases in precipitation in north and northwestern Alaska (20-25%) and smaller increases (a few %) or possibly decreases (up to 10%) along the south coast with more precipitation in summer in most areas. Even with rather large increases in precipitation, it is likely that increased evaporation will exceed precipitation and result in less soil moisture throughout the state at times.

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