Climate changes bringing severe weather, floods, droughts and rising sea levels to the rest of the nation are accentuated in Alaska, the nation's only Arctic and subarctic territory, said the third National Climate Assessment, released Tuesday by the Obama administration. Alaska's dramatic changes, subject of a special section in the national report, are seen in the land and vast stretches of ice that cover much of the state, as well as the water that surrounds it.
Alaska's rapid changes -- from ice to open water, from snow-covered landscape to trees and shrubs and from permafrost to thawed soil -- are likely influencing climate patterns far to the south, said the report, which is produced by the government every few years, in accordance with the Global Change Research Act of 1990.
Alaska has warmed twice as fast as the rest of the United States over the past 60 years. Long-term warming in Alaska is evident, despite the cyclical Pacific Decadal Oscillation pattern, which entered a warm phase in the late 1970s and a cooler phase in the early 2000s, the report said.
Average annual air temperatures in Alaska have increased by 3 degrees over the past six decades, and by 6 degrees in winter, the report said. Long-term warming has heated the warm phase of the Pacific Decadal Oscillation, moderated the cool phase and brought "more extremely hot days and fewer extremely cold days," the report said. Alaska's warming is expected to continue, increasing average annual temperatures by another 2 to 4 degrees Fahrenheit by 2050, the report said.
In the ocean, summer and fall sea ice is disappearing faster than models predict, influencing the atmosphere above, the report said.
Lack of sea ice opens up vast sections of dark water that absorb heat and release it back into the atmosphere, increasing air temperatures in the Arctic and possibly influencing circulation patterns far beyond. "There is growing evidence that this has already occurred through more evaporation from the ocean, which increases water vapor in the lower atmosphere and autumn cloud cover west and north of Alaska," the report said.
For economic development, the diminished sea ice is a double-edged sword. It provides new opportunities for commerce, including additional resource extraction in the Far North, but those commercial activities pose risks of additional marine spills and other disruptions, the report said.
Glaciers in Alaska and neighboring British Columbia, already pouring freshwater into the oceans in a volume equivalent to 20 percent to 30 percent of what is coming from the immense Greenland ice sheet, are accelerating their melt, the report said. That means a short-term boost but possibly long-term problems for hydropower systems and potential problems for near-shore fisheries and the commercial harvests that depend on them, the report said.
Acidification -- the gradual lowering of pH levels as atmospheric carbon is absorbed by marine waters -- imperils fisheries in Alaska, a state that provides half of the nation's commercially harvested seafood, the report said.
Lakes are changing size and shape in response to a warming climate, affecting migrating birds and raising the specter of problems for indigenous hunters who depend on those birds for food, the report says. In the southern two-thirds of Alaska, most lakes are shrinking in size, due in part to permafrost thaw and increased evaporation in warmer temperatures, the report said. In more northern areas, where permafrost layers are continuous, lakes will likely increase in size as the frozen ground thaws, the report said.
On land, the ground slumps caused by permafrost thaw is expected to add 10 to 20 percent -- $3.6 billion to $6,1 billion -- to the cost of maintaining Alaska's public infrastructure over the next 20 years, the report says. Affected facilities include buildings, pipelines, roads and airports. Water supplies and sewage systems in rural parts of the state are also at risk, the report says.
Vegetation changes, including increased wildfires, have mixed effects. Berry and mushroom crops have been boosted, the Interior Alaska growing season has expanded by 45 percent over the last century, and habitat for moose has improved. But habitat for lichen-eating caribou is diminished, threats from invasive species are growing and the increasing number of wildfires means more wood-smoke problems for Alaskans, the report said.
Those terrestrial impacts affect areas far beyond Alaska.
Permafrost soils in the Arctic contain almost twice as much carbon as is in the atmosphere, so thaw increases that atmospheric load. Permafrost thaw also results in methane releases from lake bottoms. Wildfire smoke spreads carbon into the skies, past state borders. The Yukon River basin, formerly a valuable carbon sink, has had those powers "substantially weakened since the 1960s by the combination of warming and thawing of permafrost and by increased wildfire." The northward spread of trees and shrubs does provide some carbon-absorption capabilities, but those benefits are offset by the albedo effect caused when a formerly white, snowy landscape turns dark with vegetation, the report said.
In all, "This spectrum of changes in Alaska and other high-latitude terrestrial ecosystems jeopardizes efforts by society to use ecosystem carbon management to offset fossil fuel emissions," the report said.
Though warming has not been as dramatic elsewhere in the United States as in Alaska, it has been steady in most of the country, according to an analysis published Tuesday in Eos, the newspaper of American Geophysical Union.
Since 1895, temperatures in the United States have risen by 1.5 degrees, with most of the increase coming since 1970, according to the analysis.
Extreme precipitation is likely to increase in all regions of the nation, and all except Alaska are expected to have longer stretches of days without precipitation -- dry periods -- between those extreme events, the AGU analysis said.
Recent conditions in much of Alaska have matched documented warming trends, though meteorologists and climate scientists point out that short-term weather can vary widely and often diverts from long-term patterns.
Several warm-temperature records were set or tied over the weekend in Alaska, topping out with the official 69-degree readings recorded at McGrath and Yakutat, according to the National Weather Service.
Water temperatures in parts of the Gulf of Alaska are running above normal, according to National Oceanic and Atmospheric Administration data. Temperatures at Kodiak, which average 41 degrees in May, are already 45.3 degrees; water temperatures are 50.5 degrees at Valdez, compared to the May average of 47 degrees, according to NOAA.
National Climate Assessment - Alaska
By YERETH ROSEN