Cooler Arctic temperatures in the summer of 2013 moderated the record sea ice loss and dramatic melting of the Greenland ice sheet seen in 2012, according to the annual Arctic Report Card released last week by the National Oceanic and Atmospheric Administration.
But this has only temporarily slowed the region's transformation into a much warmer and greener place, the report also notes, as regional extremes continued this year with record low spring snow cover in Eurasia and record high summer temperatures in Alaska.
"The Arctic caught a bit of a break in 2013," David M. Kennedy, NOAA's deputy undersecretary for operations, said last week. "But the relatively cool year in some parts of the Arctic does little to offset the long-term trend of the last 30 years."
The NOAA report on the Arctic shows how this year fits into the longer-term climatic changes taking place there:
2012 was the Arctic's 6th warmest year on record
Since the mid 1960s, temperatures in the Arctic have risen by about 3.6 Fahrenheit degrees – more than twice as much as most of the rest of the planet. Last year, the last complete year for which records are available, the average annual temperature in the Arctic was the sixth warmest on record.
Temperatures have risen everywhere across the Arctic, rather than warming in some places and cooling in others. This means that global warming, rather than natural climate variability, is the more likely explanation for the Arctic's rapidly changing climate.
Sea ice extent larger in 2013 than 2012, but still 6th smallest on record
The amount of sea ice that covers the Arctic Ocean reached its annual minimum in mid-September, falling to about 1.97 million square miles – larger than last year's record low of about 1.54 million square miles, but still more than 17 percent below the 1981-2010 average and the sixth-lowest since records began in the late 1970s.
Since 1979, the seven lowest sea ice extents on record all occurred between 2007 and 2013, according to the National Snow and Ice Data Center.
Old, thick ice is rapidly being lost
If sea ice extent represents a bird's-eye view of the Arctic, the fish's-eye view also tells a similarly dramatic story: sea ice is not only shrinking on the surface, it's also thinning rapidly in the water below.
Scientists use ice thickness as a gauge for its age; older ice is generally thicker ice. By that measure, the amount of very old, thick ice that remains at the end of the Arctic winter in March has dropped dramatically over the past 30 years – only 7 percent of the ice cover at the end of winter 2013 was old, thick ice.
Snow cover was below average – again
Seasonal snow covers the Arctic land surface for about nine months of the year, in addition to the sea ice and glaciers that remain there year-round. When there's less snow on the ground, thanks to earlier melting, the ground absorbs much more sunlight.
This May brought record losses in spring snow cover in the Eurasian Arctic – that region's sixth year in a row with record-setting snow extent losses in May or June – while North America experienced its fourth-lowest spring snow cover extent on record.
Reindeer, caribou populations are shrinking
Wild herds of reindeer and caribou, both vitally important to the lives of native Arctic and Subarctic societies, reportedly showed unusually low population numbers in 2013 and their winter ranges are smaller than in past years.
As NOAA reports (shown in the map below), only a handful of herds increased or were stable at high numbers this year; most estimates show herds declining, or remaining at low levels after sharp drops in their populations in recent years.
The land is becoming greener
Since observations began in 1982, the density of the vegetation on Arctic land – like tundra – has been on the rise. In the North American Arctic, this greening of the Arctic has accelerated since 2005.
With the exceptions of western Alaska and parts of Siberia, the tundra has grown greener over the past three decades all across the Arctic.
On the Greenland ice sheet, melting is back to normal
Last year brought record-breaking melt on the Greenland ice sheet, as an estimated 97 percent of the ice sheet's surface experienced some degree of melting during its summer peak. In July 2013, the maximum area of melting was 44 percent – far below the 2012 melt, but still the 14th highest in 33 years of record-keeping.
With less sea ice, Arctic waters are warmer
As Arctic sea ice declines and more open water is exposed at the height of summer, ocean temperatures near the remaining ice are much warmer today than they have been historically, NOAA reports. The map below shows where Arctic sea surface temperatures in August 2013 were warmer and cooler than the 1982-2006 average.
Some rare good news: Atmospheric soot is decreasing
Since the early 1990s, the amount of black carbon (also called soot) in the atmosphere over the Arctic has declined by 55 percent, NOAA reports, a rare boon for its albedo, the reflectivity of its surface. Black carbon darkens ice and snow, causing the soot-covered areas absorb more sunlight, which leads to more surface warming.
Read the complete Arctic Report Card for 2013 at NOAA.
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