Last year was one of the world’s 10 warmest years on record going back to 1880, according to reports from two U.S. agencies.
The National Oceanic and Atmospheric Administration ranked 2012 the 10th-warmest on record, with an average temperature of 58.03 degrees (14.46 Celsius). It was the 36th consecutive year to exceed the 20th-century average of 57 degrees, according to NOAA’s National Climatic Data Center in Asheville, North Carolina.
“The long-term warming trend, including continual warming since the mid-1970s, has been conclusively associated with the predominant global climate forcing, human-made greenhouse gases, which began to grow substantially early in the 20th century,” James E. Hansen, director of NASA’s Goddard Institute for Space Studies in New York and the lead author on a study of 2012 temperatures, said in the report.
The National Aeronautics and Space Administration ranked 2012 the ninth-warmest year on record. There are small differences in the data the agencies use, said Thomas R. Karl, director of the climatic data center.
Last week, NOAA announced 2012 was the warmest year in the U.S. in records begun in 1895. The nation’s warming trend is a reflection of both natural variation and the impact of climate change, according to the climatic center.
“Including 2012, all 12 years to date in the 21st century rank among the 14 warmest in the 133-year period of record,” NOAA said in a statement. “Only one year in the 20th century -- 1998 -- was warmer than 2012.”
The most extreme temperatures were recorded in the Arctic and the middle of North America, according to Hansen’s paper. The warming in the U.S. was exacerbated by this year’s drought, the worst on record since the 1930s.
The lack of soil moisture eliminated the chance for evaporative cooling in the summer, he wrote.
Extreme outbreaks of heat are becoming more common, Hansen wrote. In 2010 they struck Eastern Europe, including Moscow. In 2011 Oklahoma, Texas and northern Mexico suffered. Last year an area from the Rocky Mountains to the Great Plains was abnormally warm.
Where this record heat will appear depends on summer weather patterns, he said. The overall pattern “is an expression of increasing global warming,” Hansen wrote.
“Some seasons continue to be unusually cool even by the standard of average 1951-1980 climate, but the climate dice are now sufficiently loaded that an observant person should notice that unusually warm seasons are occurring much more frequently than they did a few decades earlier,” Hansen wrote.
The five-year mean global temperature has been relatively flat, which has caused some people to think climate change has stopped, Hansen wrote.
It hasn’t stopped, Hansen said in a conference call today with reporters. A number of factors can explain the flattening of temperatures, including more sunlight-reflecting particulates in developing nations, which are burning more coal. He also cited natural variations in water temperature in the Pacific Ocean.
Since 2008, La Nina, a pattern of lower-than-normal sea surface temperatures in the Pacific, has been dominant and affected the world average, Hansen said. He expects the temperature to rise the next time an El Nino, or warmer Pacific, is recorded.
“On the decadal time scale it is going to get warmer because we know the planet is out of energy balance,” Hansen said during the conference call. “We can predict with confidence the next decade is going to be warmer than the present one.”
Last year posted record low sea ice in the Arctic while having record high amounts in the Antarctic.
Arctic sea ice dropped to 1.32 million square miles on Sept. 16, the least seen in the satellite era, which began in 1979. Ten days later at the South Pole, Antarctic sea ice peaked at 7.51 million square miles, which was the most ever recorded.
Ice in the two regions reacts differently because of geography and weather patterns, Karl said on the call. The Arctic is an ocean and once the ice is gone the air temperature warms to match the underlying ocean, while the Antarctic is a continent surrounded by oceans.