The Arctic may not have set new record lows for sea ice cover this year, but long-term warming over the past three decades continues to increase vegetation, drive species migrations, shift ice and snow patterns and spark dramatic changes to the polar ecosystem, according to a federal analysis released yesterday.
In its annual "Arctic Report Card," the National Oceanic and Atmospheric Administration reported a series of regional Arctic extremes in 2013, including a record 36-day heat streak in Fairbanks, Alaska, as well as record high temperatures in swaths of Alaskan and Canadian permafrost 20 meters below the surface. August sea surface temperatures rose several degrees higher than the long-term average in the Barents and Kara seas, and the Arctic continues a long-term greening trend overall.
Amid warming, the growing season for Arctic vegetation has increased roughly nine days each decade since the early 1980s, NOAA said.
"About every aspect of Arctic life has potential to be affected by these changes," said David Kennedy, deputy undersecretary for operations at NOAA, in releasing the report at the American Geophysical Union conference in San Francisco. This year's report -- which covered everything from ultraviolet radiation in the Arctic to muskoxen -- included contributions from 147 authors in 14 countries.
Arctic sea ice hits its annual low in September, before reforming in the fall. This year, the annual minimum was about 50 percent higher than in 2012, a dynamic that prompted skeptic attacks about Arctic cooling this year. The report emphasizes, however, that this year's extent still fits with a long-term warming trend and that it is typical for there to be a rebound year after an unprecedented low in ice.
"We can't expect to be smashing records every year. There are going to be ups and downs, but those ups and downs are going to be superimposed on nevertheless a trend to a warmer Arctic," said Martin Jeffries, science adviser for the U.S. Arctic Research Commission.
Thin ice rather than none
Despite the more extensive ice in comparison to 2012, this year's extent ranks as the sixth-lowest since the beginning of satellite observations, and the seven lowest Arctic ice minimums have occurred in the last seven years. In another sign of warming, the existing ice cover continues to be dominated by first-year ice. In March 1988, about 58 percent of the cover consisted of this first-year ice, compared to 78 percent in the same month this year, according to the report.
When Arctic ice melts, it opens up dark areas of ocean that absorb heat, rather than reflecting it back into space. This helps drive further melt and makes it harder for surface waters to refreeze in the fall. "The ice that does form is thinner than it has been a number of years ago," Jeffries said.
"Also on land, lake ice break-up in spring 2013 was earlier than average throughout much of the Arctic, and ice duration was shorter than average in many regions," the report states. In the Beaufort Gyre, an ocean current, heat content in the summer is about 25 percent higher than it was in the 1970s, the scientists said.
The higher level of sea ice extent this year, as well as the less extensive surface melting on the Greenland ice sheet, stems from natural weather patterns, such as changes in storm intensity from 2012 and natural cloud cover variations, they said.
This year-to-year variability was apparent on the Greenland ice sheet, where 44 percent of the surface melted during the summer, in comparison to 2012's 97 percent. Summer temperatures over Greenland were about 1 to 2 degrees Celsius cooler than last year, partially because the diversion of warm air masses spurred cooler and cloudier weather than normal.
This year's report introduces two new sections on black carbon and marine fishes. Black carbon -- formed by the incomplete combustion of fuels like wood and dung -- contributes to melt by darkening the Arctic surface and enhancing absorption of solar radiation.
Levels of the sooty substance declined 55 percent at a measuring station in Canada and 45 percent at a location in Alaska since the early 1990s, largely because of emission declines from the former Soviet Union, the report said.
Tundra fires develop
However, tundra vegetation is becoming more vulnerable to wildfires, fueled by a warmer, drier climate, said Jeffries. Because wildfires are a significant source of black carbon, "it seems reasonable to ask, how much might that increase offset the decline in black carbon from other sources?" he asked.
A study this fall also suggested that oil and gas production may play a disproportionate role with Arctic soot (ClimateWire, Sept. 13).
The status of Arctic species is mixed. Muskoxen generally have increased their numbers across their range since the 1970s, partially because of reintroduction and conservation efforts. Many reindeer and caribou herds, on the other hand, are at low levels, and are experiencing contracting winter ranges.
Harvested marine fishes such as Atlantic mackerel have moved poleward into the Arctic, and the Atlantic cod in the Barents Sea is at a historical high, said Jeffries. However, the cost and remoteness of the Arctic have made sampling of fish difficult, and there is a need for comprehensive surveys to establish base-line numbers for species, according to the report.
Kathy Crane of NOAA's Arctic Research Program said there are concerns about long-term abilities to observe the region, considering recent funding pressures. Large regions of the Arctic that are now without sea ice cover in the summer are not mapped, she said.
"The U.S. is investing quite a lot of money in Arctic observing, but the fact remains that the Arctic remains a data-sparse region," Jeffries said.
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500