The Earth has apparently entered a new climate regime in which it is locked into warmer than normal temperatures. In 2012 - the temperature of the globe once again rose above the long-term average, joining the 35 years preceding it.
Specifically, the Earth’s temperature in 2012 was 1.03°F warmer than the 20th century average, the 10th warmest year since records began in 1880 NOAA announced today. NASA, which independently evaluates global temperature records, found it was the 9th warmest year on record.
Most of the warmest years on record have occurred since the turn of the millenium. According to NOAA’s analysis, all 12 years of the 21st century rank among the 14 warmest on record.
Global surface temperature difference from average 1884 to 2012. Source: NASA Goddard Institute for Space Studies
“One more year of numbers isn’t in itself significant,” NASA climatologist Gavin Schmidt said. “What matters is this decade is warmer than the last decade, and that decade was warmer than the decade before. The planet is warming. The reason it’s warming is because we are pumping increasing amounts of carbon dioxide into the atmosphere.”
Although the global temperature was elevated in 2012, temperatures were not warmer than average uniformly over the globe.
“[M]ost of Alaska, far western Canada, central Asia, parts of the eastern and equatorial Pacific, southern Atlantic, and parts of the Southern Ocean were notably cooler than average,” NOAA reported.
But these cooler than normal spots were outweighed by much warmer than average conditions in North and South America, much of Europe and Africa, and western, southern, and far northeastern Asia.
Warmth was especially intense over the United States which logged its warmest year on record.
Satellite measurements of global temperature - which serve as an independent check of NOAA/NASA temperatures obtained from thermometers - indicate it was the 9th warmest of the last 34 years.
A pause in the warming?
Although temperatures are now warmer than the 1970s and earlier decades, some scientists and journalists point to an apparent pause in the warming which began in the late 1990s, suggesting climate change may not be occurring as quickly as predicted.
There is an entire scientific literature proposing several explanations for the pause. At the top of the list is the prevalence of La Nina events over the past decade - which result in episodic cooling of the tropical Pacific ocean and lower global temperatures. 2012 was yet another La Nina year.
Such La Nina events occur somewhat randomly and are difficult to predict.
Although the average global temperature has not warmed appreciably since the late 1990s and a new global temperature record has not been established (since 2005 or 1998, depending on the analysis), 2012 was the warmest La Nina year on record besting 2011, the previous recordholder.
Should La Nina’s opposite phase, El Nino, make a strong return, the tropical Pacific would warm and a spike in global temperatures would likely follow. There have been only two El Ninos in the last 14 years.