Digital Version of November/December 2014 Print Edition
Arctic ice cover at fifth lowest annual maximum
The maximum amount of ice covering the arctic this winter was the fifth lowest since satellite data began to be kept in 1978, according to the Boulder, CO-based National Snow & Ice Data Center (NSIDC). The amount of coverage varies by year, but overall trends point to greenhouse gas emissions as a major cause of the shrinking ice, an NSIDC expert says.
The average extent this March was 5.7 million square miles, which is 282,000 square miles below the 1981 to 2010 average. The timing of the ice’s maximum extent varies by year; this year it was March 21st, but on average it's March 9th. The coverage was also 127,000 square miles above the record March monthly low, which occurred in 2006.
The linear rate of ice decline from 1978 to this year has been a 2.6% per decade decline. Air temperatures also remained unusually high throughout the Arctic during the second half of March, at 4 to 11 degrees Fahrenheit above the 1981 to 2010 average. The percentage of the Arctic consisting of ice at least five years or older is at 7%, half of what it was in February 2007.
It’s difficult to know the exact reasons for the warming trend, NSIDC research analyst Julienne Stroeve told Government Security News. But many available studies seem to suggest that the shrinkage is due “to about half greenhouse gasses” at a minimum, she says, as opposed to natural climate fluctuations, for example. “If you run a climate model and don’t add greenhouse gasses it won’t show this decline.” Virtually “all models show the ice is going down. …We know we’re warming.” As ice recedes, she says, water can be more easily warmed by the sun, which leads to more ice loss.
She adds that she “expects the trend to continue.” But climate models suggest that reducing greenhouse gases could significantly slow the changes, she says. “It’s not an irreversible process.”