The Arctic lost record amounts of sea ice last year and is changing at an unprecedented pace due to climate change, a landmark climate study says.
Last year was among the 10 warmest years on record – ranking eighth or ninth depending on the data set, according to a report led by the National Oceanic and Atmospheric Administration (Noaa). The year 2012 also saw record greenhouse gas emissions, with concentrations of carbon dioxide and other warming gasses reaching a global average of 392.7 parts per million for the year.
"The findings are striking," Kathryn Sullivan, Noaa's acting administrator, said on a conference call. "Our planet as a whole is becoming a warmer place."
The scientists were reluctant to point directly to the cause of the striking changes in the climate. But the annual reports are typically used by the federal government to prepare for the future, and in June president Barack Obama used his climate address to direct government agencies to begin planning for decades of warming atmosphere and rising seas.
The biggest changes in the climate in 2012 were in the Arctic and in Greenland, said the report, which is an annual exercise by a team of American and British scientists. The Arctic warmed at about twice the rate of lower latitudes, the report found. By June 2012, snow cover had fallen to its lowest levels since the record began. By September 2012, sea-ice cover had retreated to its lowest levels since the beginning of satellite records, falling to 1.32 million square miles.
That was, the report noted, a whopping 18% lower than the previous low, set in 2007, and a staggering 54% lower than the mark for 1980.
The changes were widespread on land as well, with record warm permafrost temperatures in Alaska and in the Canadian Arctic, the report's authors noted. On 11 July last year, Greenland experienced surface melting on 97% of the ice sheet. The record-breaking events indicate an era of "new normal" for the climate, the researchers said.
"The record or near-records being reported from year to year in the Arctic are no longer anomalies or exceptions," said Jackie Richter-Menge, a civil engineer with the US army corps of engineers. "Really they have become the rule for us, or the norm that we see in the Arctic and that we expect to see for the forseeable future."
That ice melt was also a major cause of sea-level rise, the report found. Global sea levels rose to record highs last year, after being depressed during the first half of 2011 because of the effects of La Niña. The average global sea level last year was 1.4in above the 1993-2010 average.
"Over the past seven years of so, it appears that the ice melt is contributing more than twice as much to the global sea level rise compared with warming waters," said Jessica Blunden, a climatologist at Noaa's national climactic data centre.
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