2007: Fifth warmest year on record
The data is in, and 2007 finished as the 5th warmest year on record for the globe, according to figures released by the National Climatic Data Center. For land areas only, 2007 ranked as the warmest year on record. For the oceans, 2007 was the ninth warmest year on record. La Niña continued to strengthen at the end of the year, creating ocean surface temperatures in large areas of the central and eastern equatorial Pacific more than -3°F (-1.7°C) below average. The rapid decay of the El Niño event that rang in 2007 and subsequent development of a moderate La Niña event caused the failure of the forecast issued by the United Kingdom Meteorological Office on January 4 of 2007, predicting a a 60% chance that 2007 would be the warmest year on record. The forecasters cited the combined influence of the continuing global warming trend, and the presence of a moderate El Niño event.
Figure 1. Global temperatures (land plus ocean) for 1880-2007. Image credit: National Climatic Data Center.
The warmest years on record globally were 2005 and 1998, when the global average temperatures were 1.08°F and 1.04°F higher than the long-term average of 57°F. The 2007 temperature was .99°F above average. Seven of the eight warmest years on record have occurred since 2001, part of a rise in temperatures of more than 1°F (0.6°C) since 1900. Within the past three decades, the rate of warming in global temperatures has been approximately three times greater than the century scale trend. All ten of the top ten warmest years for the globe have occurred since 1995. The global temperature record goes back to 1880.
Tenth warmest year on record for the U.S.
For the contiguous U.S., 2007 was the tenth warmest year on record. U.S. weather records go back to 1895. Six of the 10 warmest years on record for the contiguous U.S. have occurred since 1998, part of a three decade period in which mean temperatures for the contiguous U.S. have risen at a rate near 0.6°F per decade.
Figure 2. U.S. temperatures for 1895-2007. Image credit: National Climatic Data Center.
Arctic sea ice remains near record low levels
December 2007 Northern Hemisphere sea ice extent was the second lowest on record for the month of December, 13% below its extent in 1979 when satellite measurements began, according to the National Snow and Ice Data Center. December was the second straight month that a new monthly minimum Arctic sea ice record was not set, following a string of five months in a row where monthly records were set. However, the December 2007 sea ice extent was very close to the record low extent set in 2006, and the ice is much thinner than it was in 2006. This will likely cause a very early melting season and a probable return to record lows by April.