November 24, 2011
Observed ice extent record (black) over the 1870–1995 calibration interval and ice extent predicted by the reduced calibration sets during cross-validation, for four distinct reconstruction steps. Image and caption courtesy of Nature. Click image to enlarge.
The study, which was led by Christophe Kinnard of Chile's Centro de Estudios Avanzados en Zonas Aridas, used terrestrial proxies including ice cores, lake sediments, tree ring data, and historical sea ice observations from the Arctic region to reconstruct past summer sea ice extent, the period when Arctic sea ice is at its minimum. They conclude that "both the duration and magnitude of the current decline in sea ice seem to be unprecedented for the past 1,450 years" and blame higher Atlantic water temperatures, which they link to human-caused climate change, for the trend.
This year summer sea ice levels fell to the second-lowest extent since record-keeping began in 1979, according to the National Snow and Ice Data Center (NSIDC). The lowest-ever extent occurred in 2007.
Predictions range widely, but many experts expect the Arctic to be free of sea ice entirely within a few decades. By almost all standards, however, sea ice is disappearing faster than expected, partly a consequence of a positive feedback loop triggered by retreating ice. Sea ice typically helps cool the Arctic by reflecting sunlight back into space. But when sea ice melts, the dark areas of open water absorb the sun's radiation, warming the region and worsening melting.
Environmentalists are concerned that the loss of summer sea ice could have dramatic implications for wildlife -- like polar bear and walrus -- that depend on pack ice for feeding.
The loss of sea ice is also driving more exploitative industries, such as gas and oil, into once untouchable regions; however burning the fossil fuels lying beneath the Arctic will only worsen climate change, and thereby exacerbate ice loss in the Arctic.
CITATION: Christophe Kinnard, Christian M. Zdanowicz, David A. Fisher, Elisabeth Isaksson, Anne de Vernal & Lonnie G. Thompson. Reconstructed changes in Arctic sea ice over the past 1,450 years. 24 November Nature Vol 479 509-512