NASA's Goddard Institute for Space Studies is just out with its summary of global temperatures for the year just ended, and says 2009 tied as the second-warmest year globally since modern records began in 1880. Their release is HERE.
2005 remains the warmest year on the books, says NASA, "putting 2009 in a virtual tie with a cluster of other years — 1998, 2002, 2003, 2006, and 2007 — for the second warmest on record." The graph below was supplied by NASA. Click on it to enlarge.
"There's always interest in the annual temperature numbers and a given year's ranking, but the ranking often misses the point," said James Hansen, Goddard's chief, in the release. "There's substantial year-to-year variability of global temperature caused by the tropical El Nino-La Nina cycle. When we average temperature over five or ten years to minimize that variability, we find global warming is continuing unabated."
El Nino, you'll recall, is a giant patch of unusually warm water that forms along the equator in the Pacific, altering the paths of jet streams that pass over it and generally raising temperatures downwind for several thousand miles. La Nina is the opposite — a cool patch, which alternates irregularly with El Nino. 1998 and 2005 had strong El Ninos (there's another now), making them warmer. 2008, says NASA, was a La Nina year, cooling things off.
NASA says 2009 was warm globally (and the warmest on record for the southern hemisphere) despite cold winter weather in the United States. Hansen: "The contiguous 48 states cover only 1.5 percent of the world area, so the United States' temperature does not affect the global temperature much."