Many observations including increasing air temperatures, changing precipitation patterns, decreasing snow, sea-ice and permafrost extent, and glacial retreat indicate that the climate of Alaska is changing.

Observed Changes
Temperatures
Alaska has experienced the largest regional warming of any state in the U.S. Temperature records for 25 stations across Alaska from 1949 to 1998 document seasonal mean temperature increases throughout the entire state². Seasonally, increases were highest in winter and spring and lowest in summer; fall was the only season in which slight decreases were observed. Much of this warming appears to have occurred during a sudden Arctic atmospheric and ocean regime shift around 1977¹.

At 2.2°C, the most pronounced increases from 1949 to 1998 were found in winter in the Interior region². Mean annual temperatures in the different climatic regions of Alaska increased by 0.8° to 1.9°C from 1951 to 2001; most of this warming was also coincident with the 1977 Arctic atmosphere and ocean regime shifts¹. In northern Southeast Alaska, temperatures increased as much as 1.5 to 3° F in the last 60 years, with largest increases during the winter months¹³. Substantial warming in the Arctic has been documented over the last few decades. Mean annual surface temperature changes range from 2 to 3°C in Arctic Alaska¹. Arctic warming trends are most evident in winter and spring, and are twice the global average.

Credit: Alaska Climate Research Center

Water Balance
Observed warming in Alaska has been accompanied by a 30% increase in precipitation between 1968 and 1990¹. Total precipitation in the Arctic has increased at a rate of about 1% per decade over the past century. However, on the Kenai Peninsula, precipitation records between 1944 and 2002 indicate a nearly 40% decrease in the mean annual water balance, which is the difference between precipitation and potential evapotranspiration⁴. Small changes in water balance are sufficient to alter surface soil or ground water and can lead to drying of wetlands. In northern Southeast Alaska, mean winter temperature began exceeding 0° C in the mid-1980’s resulting in a reduction of total annual snowfall from 109 inches to 93 inches, despite higher total precipitation. ¹³

Snow and Sea-ice
According to the Intergovernmental Panel on Climate Change, satellite data indicate that snow-cover extent in the Northern Hemisphere has decreased by about 10% since the late 1960s¹¹. September Arctic sea ice extent declined by 7.8% per decade from 1953 to 2006 and by 11.7% per decade from 1979 to 2008⁶. During the 2007 melt season Arctic sea ice reached its lowest extent since satellite measurements began in 1979. At 1.65 million square miles, sea ice extent for the month of September 2007 was 23 percent lower than the previous September record set in 2005, and 39 percent below the long-term average from 1979 to 20007. Minimum ice extent in September 2008 was 9% greater than 2007, making 2008 the second lowest year on record. Sea-ice researchers note that the extent of thin, first-year ice was high in 2008, and that such ice is prone to rapid melting the following summer. Because thicker multi-year ice is rapidly declining and is being replaced by thin first-year ice during the winter, the total volume of arctic sea ice is believed to have reached a record low in 2008.

This image compares the average sea ice extent for September 2007 to September 2005; the magenta line indicates the long-term median from 1979 to 2000.

Credit: National Snow and Ice Data Center

Permafrost
Permafrost, or permanently frozen ground, is soil, sediment, or rock that remains at or below 0°C for at least two years. North of the Brooks Range, permafrost occurs as a continuous sheet extending from a few inches below the surface down as much as 1000 feet¹. Although permafrost may occur in any region where the average annual temperature is freezing or below, it gets progressively thinner and discontinuous in extent until nearly entirely absent in Southeast Alaska and along the Aleutian Islands. Permafrost physically supports the ground surface, controls soil temperature and moisture, modifies microtopography, controls subsurface hydrology and rooting zones, and influences nutrient cycling. Borehole measurements taken along a north-south transect of Alaska document permafrost warming throughout most of the region. Total warming at the permafrost surface between 1977 through 2003 was 3 to 4 °C for the Arctic Coastal Plain, 1 to 2 °C for the Brooks Range including its northern and southern foothills, and 0.3 to 1 °C south of the Yukon River⁸. Rising temperatures, degradation of permafrost, and loss of shore-fast ice along Alaska’s coasts exposes coastlines and coastal villages to increased coastal erosion and vulnerability to storm surges.

The thawing of ice-rich permafrost causes subsidence of the land surface, creating thermokarst ponds and causing trees to tilt, which is shown in this peatland terrain in Churchill, Manitoba.

Glaciers
The glacial mass balance record (the net gain or loss of ice over a year) has been negative for Alaska statewide since the mid-20th century, averaging approximately 11 km³/year from 1965 to 1993⁹. Conditions for individual glaciers vary. While most Arctic glaciers have experienced predominantly negative balances over the past few decades, some may be positive where winter precipitation has increased⁹. The mountains around the Gulf of Alaska contain up to 90,000 km² of glacier area including the largest glaciers outside of the polar regions. Longterm mass-balance time series for three relatively small glaciers in that region indicate that these glaciers follow a regional and global trend of accelerated melting since 1988¹⁰. These changes also affect the seasonal discharge and turbidity of glacial streams¹³.

Projected Trends
Climate projections suggest a continuation of the warming trends of recent decades¹¹. Changes are expected to be greatest during winter months. Because ice and snow have greater reflectivity, reduced snow and sea-ice extent reveals darker land and ocean surfaces, increasing absorption of the sun’s heat and causing further regional warming¹¹. While northern and western Alaska may experience increases in precipitation, southeast Alaska may experience a decrease. Permafrost thawing is projected to accelerate under future warming, with as much as the top 30 feet of discontinuous permafrost projected to thaw by the end of the 21st century¹. The accelerated mass loss of Alaskan glaciers that began by the end of the 1980s is likely to continue into the future¹².

Related Links
Alaska Center for Climate Assessment and Policy
Center for Global Change & Arctic System Research
Alaska Climate Change Strategy
Alaska Climate Research Center
National Snow And Data Center

Sources
¹Parson, E.A., L. Carter, P. Anderson, B. Wang, G. Weller. 1999. Potential Consequences of Climate Variability and Change for Alaska. U.S. Global Change Research Program. International Arctic Science Committee. Center for Global Change and Arctic System Research. Fairbanks, Ak. 30 pp. (pdf)

²Stafford, J.M., G. Wendler, and J. Curtis. 2000. Temperature and precipitation of Alaska: 50 year trend analysis. Theor. Appl. Climatol. Vol. 67: 33-44. (pdf)

⁴Klein, Eric. Berg, Edward. Dial, Roman. "Wetland drying and succession across the Kenai Peninsula Lowlands, South-Central Alaska." Canadian Journal of Forest Research (2005): pubs.nrc-cnrc.gc.ca/rp/rppdf/x05-129.pdf.

⁵IPCC. 2001. Climate Change 2001: Synthesis Report. A Contribution of Working Groups I, II, and III to the Third Assessment Report of the Integovernmental Panel on Climate Change [Watson, R.T. and the Core Writing Team (eds.)]. Cambridge University Press, Cambridge, United Kingdom, and New York, NY, USA, 398 pp. (pdf)

⁶Stroeve, J., M. M. Holland, W. Meier, T. Scambos, and M. Serreze (2007), Arctic sea ice decline: Faster than forecast? Geophysical Research Abstracts, Vol. 9, 01362. (pdf)

⁷National Snow and Ice Data Center Arctic Sea Ice News Fall 2007 web page accessed June 15, 2008. (pdf)

⁸Osternkamp, T.E. 2005. The recent warming of permafrost in Alaska. Global and Planetary Change. Vol. 49, Issue 3-4: pg. 187-202.

⁹Serreze, M.C., J. E. Walsh, F. S.Chapin III , T. Osterkamp, M. Dyurgerov, V. Romanovsky, W. C. Oechel, J. Morison, T. Zhang, and R. G. Barry. 2000. Observational evidence of recent change in the northern high-latitude environment. Climatic Change 46: 159–207.

¹⁰Meier, M.F. and M. B. Dyurgerov. 2002. How Alaska Affects the World. Science. Vol. 297:350-351.

¹¹ACIA, 2005.Arctic Climate Impact Assessment. Cambridge University Press, 1042p. (pdf)

¹²Dyurgerov, M.B. and M.F. Meier. 2005. Glaciers and the changing earth system: A 2004 snapshot. Institute of Arctic and Alpine Research, University of Colorado. Occasional Paper No. 58. 188 pp.

¹³Kelly, B.P., T. Ainsworth, D.A. Boyce Jr., E. Hood, P. Murphy, and J. Powell. 2007. Climate Change: Predicted Impacts on Juneau. Report to City and Borough of Juneau. 86 pp. (pdf)