GENEVA — This year has ranked among the nine warmest since records began more than 160 years ago, continuing a trend for the planet that is increasing the dangers of extreme weather events, according to United Nations meteorologists.
"It confirms the trend towards a warmer planet," Michel Jarraud, head of the World Meteorological Organization at the United Nations, said in Geneva on Wednesday as he delivered a provisional assessment intended to inform policy makers and negotiators attending the U.N. Climate Change Conference in Doha, Qatar.
The final judgment on 2012 will come in March, but Mr. Jarraud said that meteorologists were not observing any major events that would greatly alter the preliminary findings.
"Climate change is taking place before our eyes and will continue to do so as a result of concentrations of greenhouse gases in the atmosphere, which have risen constantly and again reached new records," he added in a prepared statement.
Among the most conspicuous evidence of climate change associated with global warming was the "alarming" rate at which Arctic ice had melted during the summer months, he said. The melting this year occurred at a much faster rate than in 2011 and outpaced the predictions of climate experts on the Intergovernmental Panel on Climate Change, he said.
By September, the level of Arctic ice was the lowest since satellite records began and had shrunk by nearly half — an area nearly the size of India — below the average minimum level in the 20 years before 2000, the organization reported.
The ice will reform in the winter but will be thinner than before and more vulnerable to further melting, Mr. Jarraud warned. "The trend is not only continuing but accelerating," he said. "The more it melts, the faster it will melt."
The ice melt will contribute to rising sea levels that are already 20 centimeters, or nearly 8 inches, higher than a century ago, Mr. Jarraud said, posing added risks in the event of extreme weather. Hurricane Sandy would have had less impact on New York if it had occurred 100 years ago when sea levels were lower, he said.
After a chilly start to 2012, average temperatures from January to October were 0.45 degrees Celsius, or 0.81 degrees Fahrenheit, above the average from 1961 to 1990, according to the World Meteorological Organization's findings. A rise of only one degree Celsius was sufficient to increase the frequency of extreme weather events, Mr. Jarraud said.
The above-average temperatures experienced in 2012 had been marked by record temperatures in areas like Greenland, Siberia and central China, the World Meteorological Organization reported.
Much of the United States, together with parts of Europe, western Russia and southern China, had suffered severe drought, while parts of West and sub-Saharan Africa had experienced severe flooding.
Meteorologists have been at pains to make clear that no major weather event was the result of a single cause, but research into climate change was establishing clear links, Mr. Jarraud said, citing the results of research into the extreme heat wave in Russia in 2010. "Without climate change, this episode would have been very unlikely," he said.
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