WASHINGTON – The world last year wasn't quite as warm as it has been for most of the past decade, government scientists said Thursday, but it continues a general trend of rising temperatures.
The average global temperature was 57.9 degrees Fahrenheit, making 2011 the 11th hottest on record, the National Oceanic and Atmospheric Administration said. That's 0.9 degrees warmer than the 20th century average, officials said. In fact, it was hotter than every year last century except 1998.
One reason 2011 was milder than recent years was the La Nina cooling of the central Pacific Ocean. La Ninas occur every few years and generally cause global temperatures to drop, but this was the warmest La Nina year on record.
And 2011 also was the warmest year on record for Spain and Norway, and the second warmest for the United Kingdom. In the United States, it was only 1 degree above normal, which made it the 23rd warmest on record. But 17 cities -- including Houston, Miami, Trenton and Austin -- had their warmest years.
This marks the 35th straight year that global temperatures were warmer than normal. NOAA's records for world average temperatures date back to 1880.
"It would be premature to make any conclusion that we would see any hiatus of the longer-term warming trend," said Tom Karl, director of NOAA's National Climatic Data Center. "Global temperatures are continuing to increase."
NASA, which calculates global temperatures in a slightly different way, announced essentially the same temperature for the year. But NASA's record-keeping calls it the ninth warmest ever.
Both NASA climate scientist James Hansen and University of Victoria's Andrew Weaver said they expect that in the next few years the world will set yet a new record high temperature. 2010 tied for the hottest on record.
NOAA also released new figures for extreme weather. The agency recalculated the number of billion-dollar weather disasters in the U.S., bumping the total from 12 to 14. Officials added Tropical Storm Lee, which dumped rain from Maryland to New England in September, and a July hail and wind storm in Colorado to the list.
The 14 extreme events smash the old record of nine billion-dollar disasters in 2008.
"America has endured an unusually large number of extreme events, totaling damages of more than $55 billion," NOAA deputy administrator Kathryn Sullivan said. She blamed a variety of factors, including population changes.
For the year, a record 58 percent of the United States had either extreme rainfall or severe drought, about triple what is normal for the country. Seven states -- New York, Pennsylvania, Ohio, New Jersey, Massachusetts, Indiana and Kentucky -- had their wettest years since those types of records were kept beginning in 1895. Texas had its driest year ever.
The record wet up north and dry down south fits with what climate change science predicts, but it is too early to say if 2011's precipitation extremes were due to global warming, Karl said. And the unusual number of deadly tornadoes can't be linked to global warming, he said.
But Kevin Trenberth, director of climate analysis at the National Center for Atmospheric Research in Boulder, Colo., which is a consortium of universities, said it's hard not to see the hand of man-made global warming behind the extremes.
"Where these events occur is largely driven by natural variability, but the fact that they are breaking records and causing tremendous damage when they do occur is undoubtedly because of the human stimulus," Trenberth said in an email.