Climate

Arctic Death Spiral: Sea Ice Extent Hits Record Winter Low As Thickness Collapses

CREDIT: NASA

Here the 2015 maximum is compared to the 1979-2014 average maximum shown in yellow. A distance indicator shows the difference between the two in the Sea of Okhotsk north of Japan.

Arctic sea ice has been in a virtual death spiral for over three decades now with serious implications for extreme weather, sea level rise, and permafrost melt. Not only has the surface area or extent of sea ice declined sharply, but so has the ice thickness during the summer minimum (when the melt season ends in September) — dropping a remarkable 85 percent from 1975 to 2012, according to a recent study.

The extent of Arctic sea ice hits a winter maximum in early March. This year, the National Snow and Ice Data Center (NSIDC) — along with NOAA and NASA — said the maximum extent was likely reached on February 25. This was not only the second earliest maximum, “it is also the lowest in the satellite record.”

NASA explains what happened in this short video:

As NASA points out, this record low winter maximum does not guarantee a record summertime minimum. Moreover the maximum is less significant than the minimum.

“Scientifically, the yearly maximum extent is not as interesting as the minimum. It is highly influenced by weather and we’re looking at the loss of thin, seasonal ice that is going to melt anyway in the summer and won’t become part of the permanent ice cover,” explained NASA sea ice scientist Walt Meier. “With the summertime minimum, when the extent decreases it’s because we’re losing the thick ice component, and that is a better indicator of warming temperatures.”

The best indicator of the sustained impact of global warming on the Arctic is the stunning decline in the thickness of the sea ice that has accompanied the shrinking of its surface area. A February study published in The Cryosphere, “Arctic sea ice thickness loss determined using subsurface, aircraft, and satellite observations,” offers the most comprehensive and up-to-date analysis of the Arctic death spiral, combining eight different data sets, including ones from submarines, aircraft, and satellites. This study’s conclusion is alarming:

… annual mean ice thickness has decreased from 3.59 meters [11.8 feet] in 1975 to 1.25 m [4.1 feet] in 2012, a 65% reduction. This is nearly double the 36% decline reported by an earlier study….

In September the mean ice thickness has declined from 3.01 to 0.44 m [from 9.9 to 1.4 feet!], an 85 % decline.

“The ice is thinning dramatically,” explained climatologist Ron Lindsay, the lead author — much faster than previously estimated. The study includes this chart of the average annual sea ice thickness, in meters, for the central Arctic Ocean, in recent decades:

Arctic Sea Ice

The steadily dropping trend (in meters) of average annual sea ice thickness (green line) is compared to the trend from an earlier study (orange line) for the central Arctic. Red dots are submarine records.

This thinning is faster than the researchers had expected. Co-author Axel Schweiger noted that, “At least for the central Arctic basin, even our most drastic thinning estimate was slower than measured by these observations.”

Summertime Arctic sea ice is not long for this world. Because of Arctic amplification, the Arctic warms twice as fast (or more) than the Earth as a whole does. Earlier this month, a study projected the rate of warming for the Arctic will soon exceed 1.0°F (0.55°C) per decade — and could hit 2°F per decade post-2050 if we don’t reverse carbon pollution trends ASAP.

This is especially troublesome because a key accelerator of Arctic amplification is sea ice loss. Global warming melts highly reflective white ice and snow, exposing in its place the dark blue sea or dark land, both of which absorb much more solar energy.

A great deal of recent research suggests that Arctic amplification, including sea ice loss, is already worsening extreme weather. Similarly, such amplified warming means that the rapidly-melting Greenland ice sheet, which warming has already made unstable, is likely to start collapsing even faster, which would push sea level rise higher than previously estimated, upwards of six feet this century.

Finally, a 2008 study, “Accelerated Arctic land warming and permafrost degradation during rapid sea ice loss,” concluded that “simulated western Arctic land warming trends during rapid sea ice loss are 3.5 times greater than secular 21st century climate-change trends. The accelerated warming signal penetrates up to 1500 km [930 miles] inland.” So our current period of rapid sea ice loss threatens to triple Arctic land warming, which would speed up the release of large amounts of carbon from defrosting permafrost — a dangerous amplifying feedback which could add as much as 1.5°F to total planetary warming this century.