Average annual temperature has increased since 1925, but with large multi-decadal variations; most of the increase has occurred in the winter and spring seasons. Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century.
Average annual precipitation is projected to increase by 10% or more across all of Alaska by the middle of the 21st century under a higher emissions pathway.
Late summer Arctic sea ice extent and thickness has decreased substantially in the last several decades. Climate models project that Arctic waters will be virtually ice-free by late summer before 2050.
Alaska’s vast expanse and geographical variation lead to a variety of climate types. Four main factors influence the state’s climate: its northerly latitude crossing the Arctic circle, its wide range of elevation from sea level to the highest peak in the United States, proximity (or lack thereof) to the ocean, and seasonal distribution of sea ice along its western and northern boundaries. Average annual temperatures range from the mid-40s (°F) in the south where maritime influence is strong to about 10°F in the Arctic region north of the Brooks Range. The greatest seasonal changes in temperature occur in the state’s interior where average summer maximum temperatures are in the upper 70s and average winter minimums are 20–30°F below zero. The highest temperature ever recorded in Alaska was 100°F at Fort Yukon in the interior (June 27, 1915). The coldest temperature was -80°F at Prospect Creek, also in the interior (January 23,1971).
Alaska’s temperature climate is highly variable. It was moderately warm from the 1920s into the 1940s, followed by a much cooler period from the late 1940s into the 1970s. Since the 1970s, Alaska has warmed by about 2.5°F (Figure 1), compared to about 1.5°F for the contiguous United States as a whole. Most of the warming has occurred in the winter and spring seasons, and the least amount in fall. Summer temperatures have been well above average since 1990 (Figure 2) and winter temperatures have been above average since 2002 (Figure 3a). A portion of the large decadal variability is caused by changes in hemispheric climate patterns. For example, a substantial increase in average temperature occurred around 1976, followed subsequently by more modest additional warming through 2014. Specifically, average annual temperature increased by about 1.5°F from the 1970s to the 1980s, then about 1°F from the 1980s to the 2000s. This warming coincided with a shift in a climate pattern known as the Pacific Decadal Oscillation (PDO). In the past, during the warm phase of the PDO, there has been increased flow from the south that brings warm air into Alaska during the winter. Accelerated warming has occurred since mid-2013, and the most recent two years have been the 2nd warmest (2014) and fifth warmest (2015) on record. The shift to warmer temperatures in the 1970s can be seen in the observed number of extremely cold nights (days with minimum temperature below –30°F; Figure 4). Since 1980, the number of extremely cold nights has been generally below the long-term (1930-2014) average, with the lowest 5-year average number occurring in the early 2000s. The observed number of warm days (days with maximum temperature above 80°F) was high during the 1990s and early 2000s, but has been near to or slightly below the long-term average during the past decade (Figure 3b). Over the past century, the length of the growing season in Fairbanks has increased by 45% and the number of snow free days has increased by 10%.
Average annual precipitation amounts vary greatly across Alaska. Coastal mountain ranges in the southeastern panhandle receive more than 200 inches per year, while totals drop to 60 inches south of the Alaska Range, 12 inches in the interior, and less than 6 inches in the North Slope. The record amount of rainfall to occur in a 24-hour period was 15.05 inches at Seward in southcentral Alaska in October 1986. The record maximum snowfall in a 24-hour period was 78 inches on February 9,1963 at Mile 47 Camp along Highway 4 in the southeastern portion of the state. The driest multi-year periods were in the 1950s and late 1960s/early 1970s, and the wettest period was in the late 1920s (Figure 5). The driest 5-year period was 1968-1972 and the wettest was 1928-1932. Since the late 1980s, total annual precipitation in Alaska has been above the long-term average except for a dry period in the late 1990s. There is considerable regional variability, however, as portions of interior and Arctic Alaska have observed a long-term decrease in precipitation. Also, for the summer season, the latest 5-year period (2010–2014) is the wettest on record (Figure 3c). As with average precipitation, the occurrence of extreme precipitation events is highly variable and is both regionally and seasonally dependent. Most of Alaska has seen an increase in extreme precipitation events (the heaviest one percent of 3-day precipitation totals) since the mid-20th century; however, there is no statewide average trend in the number of days with precipitation exceeding 1 inch since 1950, and the highest values occurred in the 1930s (Figure 3d).
Late summer Arctic sea ice extent and thickness has decreased substantially in the last several decades and the ice volume is approximately one half of that observed prior to satellite monitoring in 1979. The lowest minimum Arctic sea ice extent occurred in 2012 (Figure 6). Arctic sea ice plays a vital role in the climate of Alaska, the lives of its inhabitants, and the functionality of its ecosystems. Warming linked to ice loss influences atmospheric circulation and precipitation patterns, both within and beyond the Arctic. Residents of Alaska rely on sea ice for hunting and fishing and to provide a protective barrier against severe coastal storms. With the late-summer ice edge located farther north than it used to be, storms produce larger waves and cause more coastal erosion. A significant increase in the number of coastal erosion events has been observed as the protective sea ice embankment is no longer present during the fall months. In response to the increased erosion, several coastal communities are seeking to relocate.
Much of the Alaskan Interior (between the Brooks and Alaska Ranges) is a zone of discontinuous permafrost, and the area north of the Brooks Range is continuous permafrost. Increasing temperatures result in permafrost melting, which causes substantial issues relating to infrastructure (e.g. damage to buildings, pipelines, roads, airports, and water supply and sewage systems from ground subsidence), ecology, and increased greenhouse gas emissions. As the climate continues to warm, snow in Alaska melts earlier each spring, lengthening the snow-free summer season.
Wildfires are also of particular concern for the state, especially in recent years. Drying of wetlands, increased frequency of warm dry summers, and associated thunderstorms has led to a greater number of large fires during the 2000s than in any previous decade since record keeping began in the 1940s. From 2000 to 2010, the area burned by wildland fires averaged 4,200 square miles per year (1.3% of the interior), about three times the long-term average. The frequency of wildfire occurrence and severity is projected to increase with the annual area burned in Alaska projected to double by the middle of the 21st century and triple by the end of the century.
Under a higher emissions pathway, historically unprecedented warming is projected by the end of the 21st century (Figure 1). Even under a pathway of lower greenhouse gas emissions, average annual temperatures are projected to most likely exceed historical record levels by the middle of the 21st century. However, there is a large range of temperature increases under both pathways, and under the lower pathway, a few projections are only slightly warmer than historical records.
Since 1880, global sea level has risen by about 8 inches. However, in Alaska, sea level is actually falling along much of the southern coast due to isostatic rebound from ice mass loss. In other parts of the coast, tectonic activity results in mean subsidence, exacerbating the effect of sea level rise. Although global sea level is projected to rise another 1 to 4 feet by 2100 as a result of both past and future emissions from human activities (Figure 7), the changes in coastal erosion due to the combined effects of sea ice loss and permafrost/frozen soil melt are likely to cause larger impacts well before the inundation associated with sea level rise. Climate models project that northern waters in late summer could be virtually ice-free before 2050.
While historical precipitation trends are mixed, average precipitation is projected to increase in all seasons during the 21st century, with the greatest increases expected in winter and spring. By the middle of the 21st century, annual precipitation increases are projected to exceed 10% over most of the state (Figure 8).