Some of the headlines may have been deceiving, but don't be fooled: 2008 was among the hottest years ever recorded on Earth, and it concludes the hottest decade ever recorded.
The World Meteorological Organization and the National Oceanographic and Atmospheric Administration in the U.S. estimate the 2008 average temperature slightly differently, with the U.S. estimate a hair warmer than the WMO. But both agree that 2008 is the 10th warmest year ever recorded (since 1850 for the WMO or 1880 for the U.S. records), and that the span from 1998 to 2008 has seen global warming at a pace unprecedented in the age of humankind.
The U.S. estimates that the world's ocean surface temperature ranked fifth-highest ever recorded, despite the presence early in the year of La Nina conditions in the Southern Pacific Ocean, which cool a vast swath of the ocean and influence weather patterns worldwide.
The most dramatic result of the abnormally warm 2008 year was seen in the Arctic, where more ice melted than in any year other than 2007. Further, the volume of ice in the Arctic hit a new record low. Since 2003, 2 trillion tons of land ice have disappeared, with more than half that total disappearing from Greenland, according to a NASA study. (Story continues below chart.)
Besides being a visible symbol of the early effects of global warming, the melting of the Arctic represents a serious threat in and of itself. Not only does some melting ice increase sea level -- which over time will swamp low-lying communities around the globe, displacing millions of refugees -- but the melting of arctic sea ice also increases the amount of sunlight absorbed by the northern oceans and allows more methane to escape from permafrost -- both of which accelerate the warming trend in the region. Crossing some threshold of melting could lead to an irreversible slide, even if the world manages to curtail greenhouse gas emissions dramatically.
The world's recent United Nations meeting in Poznan, Poland was seen as a faltering step forward, or a failure, depending on the analyst. The prospects for a new global treaty on global warming to be signed at this time next year, in Copenhagen, are mixed.
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