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GENEVA (Reuters) - Last year tied for the hottest year on record, confirming a long-term warming trend which will continue unless greenhouse gas emissions are cut, the World Meteorological Organization (WMO) said on Thursday.
The first 10 years of the millennium proved to be the hottest decade since records began in the 19th century, it said.
"The main signal is that the warming trend continues and is being strengthened year after year," WMO Secretary-General Michel Jarraud told a news conference.
"The trend, unfortunately, will continue for a number of years but the amplitude will depend on the amount of greenhouse gases released," the Frenchman added. "It will depend on action taken to minimize the release of greenhouse gases."
Jarraud said the latest data should convince doubters about the growing evidence for man-made climate change. "If they look at it in an unbiased way, it should convince them, or hopefully a few of them, that the skeptical position is untenable."
2010 was also marked by further melting of Arctic ice -- in December its extent was at its lowest on record, the WMO said -- and by extreme weather, including Russia's heatwave and devastating floods in Pakistan.
Rising temperatures, already about 0.8 degree Celsius above pre-industrial times, mean the world will struggle to limit warming to below 2 degrees Celsius, a target agreed by almost 200 nations at U.N. talks last month in Mexico.
Many experts see 2C as a threshold for dangerous climate change, like more heatwaves, droughts, floods and rising seas.
"We have to act very fast and strongly" to limit emissions, said Bob Ward, of the Grantham Research Institute on Climate Change and Environment at the London School of Economics and Political Science.
He noted that many skeptics say global warming has stopped because of no new records since 1998, when temperatures were boosted by a strong El Nino event that warms the Pacific.
"But they cannot explain away the fact that nine of the 10 warmest years have occurred since 2000," he said.
"Data received by the WMO show no statistically significant difference between global temperatures in 2010, 2005 and 1998," the United Nations body, which compiles its ranking from data provided by British and U.S. agencies, said in a statement.
Data from British institutes on Wednesday showed last year was the world's second warmest behind 1998, while the other two main groups tracking global warming, based in the United States, said 2010 was tied for the hottest on record.
Over the 10 years from 2001 to 2010, global temperatures have averaged 0.45 degrees Celsius (0.83 degrees Fahrenheit) above the 1961-1990 average and are the highest ever recorded for a 10-year period since climate records began, WMO said.
The difference between the three hottest years was less than the margin of uncertainty in comparing the data, according to WMO, whose assessment is based on climate data from land-based weather and climate stations, ships, buoys and satellites.
The fight against global warming suffered a setback in the wake of the financial crisis, slowing funding for renewable energy projects and knocking momentum from international efforts to agree a climate deal to succeed the Kyoto Protocol in 2013.
Additional reporting by Alister Doyle in Oslo; Editing by Jonathan Lynn and Janet Lawrence