The Arctic became warmer and wetter since the beginning of the 21st century, a self-reinforcing trend likely to continue because it is linked to sea-ice melt and more persistent open-water conditions in the world's northern ocean, a newly published study concludes.
Data from NASA shows that average surface temperatures across the Arctic Ocean increased an average of 0.16 degrees Celsius per year from 2003 to 2013, and air temperatures rose 0.09 degrees Celsius annually over the same period, says the study, published online in Geophysical Research Letters.
The changes weren't evenly distributed, though. They were dominated by large increases in the November-to-April period, during which Arctic-wide surface temperatures rose 2.5 degrees Celsius and air temperatures rose 1.5 degrees Celsius from 2003 to 2013.
November saw the biggest increases in "skin temperature" (defined as temperature at the Earth's surface), and air temperature, with an average annual rise of 0.42 degrees Celsius on the surface and 0.32 degrees Celsius in the air, said the study, by Linette Boisvert of the NASA-affiliated Earth System Science Interdisciplinary Center at the University of Maryland and Julienne Stroeve, a research scientist with the National Snow and Ice Data Center in Colorado.
The NASA data also showed that moisture flux -- the transport of water vapor from the ocean to the air -- increased in nearly all the months, but grew most dramatically during months of maximum open water. The biggest increase in moisture flux over the time period came in October, followed by increases in September and August, the data showed.
The changes are linked to the sea-ice trends, Stroeve said.
Moisture and temperature changes match up with expanded annual Arctic ice melt, she said.
"The autumn is when we see the largest responses to summer ice loss. The later the freeze-up the more the temperature/water vapor feedbacks will extend into autumn," Stroeve wrote in an email. "In October there is still quite a bit of open water, but the air temperatures are dropping and so we start to get large feedbacks of amplified warming and more moisture into the atmosphere that extends into November."
Arctic sea-ice extent has diminished since satellite records began in 1979. In that period, the rate of ice-extent decline in September -- the month of minimum sea ice -- was 13.3 percent through 2014, according to the National Oceanic and Atmospheric Administration. Since the 2002 launch of the AIRS-equipped Aqua satellite, ice changes have been dramatic; the record low was hit in 2012.
The study found that moisture flux timed to ice melt also correlated with increases in heat-holding cloud cover in late fall and mid-winter, reduced cloud cover over the Beaufort Sea in summer along with earlier onset of seasonal melt and later onset of seasonal refreeze, the study found.
Arctic-wide, the study found, the onset of melt advanced by 6.2 days from 2003 to 2013 and the annual refreeze was delayed by 11.2 days.
Changes in the patterns of heat and levels of moisture flux, like the changes in sea-ice melt and freeze, are variable and not uniform throughout the Arctic, however, the study notes. The Barents and Kara seas have had the most significant speed-up of melt onset and delays in winter refreeze, for example, while surface temperatures in the Chukchi Sea showed a slight cooling trend over the 2003-2013 period.
With the heat and moisture patterns feeding into it, the Arctic-wide trend to earlier melt and later freeze is likely to continue, the study said.
Analysis of the data collected by AIRS "suggests several feedback processes are contributing to the observed lengthening of the melt season. Based on trends seen in the AIRS data, we expect the Arctic to become warmer and wetter in the future, changing to a 'New Arctic' climate, one that is dominated by processes affected by large ice-free areas for the majority of the year as the melt season lengthens," the study says in its conclusion.
Contact Yereth Rosen at yereth@alaskadispatch,com.