Last year was one of the 10 warmest on record, the National Oceanic and Atmospheric Administration said on Tuesday.
NOAA’s yearly report on the state of the climate was just released by the American Meteorological Society. The report, compiled with the help of 384 scientists across 52 countries, drew from measures of greenhouse gas concentrations, sea surface and atmospheric temperatures, sea level rise, sea ice extent and snow cover.
“Many of the events that made 2012 such an interesting year are part of the long-term trends we see in a changing and varying climate — carbon levels are climbing, sea levels are rising, Arctic sea ice is melting, and our planet as a whole is becoming a warmer place," acting NOAA Administrator Kathryn D. Sullivan said in a statement.
Depending on the dataset used, last year was either the 8th or 9th warmest on record, according to the report. It was, however, the warmest year on record for both the U.S. and Argentina. In January, NOAA had estimated that 2012 was the 10th-hottest year on record worldwide.
It was also something of a transition year for the global climate, as a La Nina phenomenon that began in mid-2011 dissipated in the spring of 2012. La Nina episodes, where sea surface temperatures across the equatorial Eastern Central Pacific Ocean are lower than normal, tend to keep temperatures down and cause dry spells in the Midwestern U.S. and elsewhere. For the rest of the year, the climate was stuck in neutral: neither a La Nina event nor an El Nino event – the reverse condition, where sea temperatures are higher than normal – dominated the landscape.
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Meanwhile, sea ice in the Arctic continues to melt into the record books. New record lows for ice coverage were set last year. In September, the coverage was just 1.32 million square miles – the lowest since satellite records started being kept in 1979. The Greenland ice sheet melt was also the largest ever observed – by mid-July 2012, 97 percent of the ice sheet showed some kind of melting, and extend greater than average by fourfold.
The oceans continue to rise and heat up. The Sea surface temperature in 2012 was one of the 11 warmest on record, and sea levels reached record highs. Across the globe, the oceans have been rising about 3.2 millimeters every year over the past 20 years.
Greenhouse gas levels also rose last year, rebounding after a period of decline linked to the global economic downturn. Atmospheric carbon dioxide concentrations increased by 2.1 parts per million in 2012, with a global average of 392.6 parts per million for the year. In spring 2012, atmospheric CO2 concentrations rose about 400 ppm at several sites in the Arctic.
Overall, the report indicates that trends in our changing climate – warming temperatures, rising sea levels, shrinking Arctic sea ice – continue apace.