Monthly Summary (Updated between the 16th and 19th of each month)
2010: tied with 2005 as globe's warmest year on record
The year 2010 was tied with 2005 as Earth's warmest year in history, according to separate calculations performed by NASA and the National Oceanic and Atmospheric Administration (NOAA). Temperatures during 2010 were 1.12°F (0.62°C) above the 20th century average. Reliable global temperature records go back to 1880. NOAA reported that the Northern Hemisphere had its warmest year on record in 2010, the Southern Hemisphere its 6th warmest, land areas their 2nd warmest, and the oceans their 3rd warmest. Global satellite-measured temperatures of the lowest 8 km of the atmosphere during 2010 were virtually tied with 1998 for warmest on record, according to the University of Alabama Huntsville (UAH). The 1998 temperatures were 0.01°C warmer than 2010, but the difference is so small that the two years should be considered tied for first place. These measurements are very sensitive to the effect of major El Niño events that warm the waters and atmosphere over the Eastern Pacific. Thus the 1998 El Niño--the strongest such event ever recorded--set a global lower atmospheric temperature record that had been impossible to match until 2010.
December 2010 11th to 17th warmest on record
December 2010 was the globe's 17th warmest December on record, according to the National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center (NCDC). NASA's Goddard Institute for Space Studies rated December 2010 the 11th December on record. December 2010 global ocean temperatures were the 10th warmest on record, and land temperatures were the 30th warmest on record. Global satellite-measured temperatures for the lowest 8 km of the atmosphere were the 7th warmest on record, according to both Remote Sensing Systems and the University of Alabama Huntsville (UAH). The global cool-down from November, which was the warmest November on record for the globe, was due in large part to the on-going moderate strength La Niña episode in the Eastern Pacific. The large amount of cold water that upwells to the surface during a La Niña typically causes a substantial cool-down in global temperatures.
For those interested, NCDC has a page of notable weather highlights from December 2010
An average December for the U.S.
For the contiguous U.S., December was near-average in temperature, ranking as the 44th coldest December in the 116-year record, according to the National Climatic Data Center. The year 2010 was the 23rd warmest on record. A strong "Arctic Oscillation" pattern allowed cold air to spill southward over the Southeast U.S., resulting in the coldest December on record in Florida and Georgia. Nine other states in the Southeast U.S. had top-ten coldest Decembers. Five states in the Southwest U.S. had top-ten warmest Decembers. A series of major snowstorms brought the 7th-largest December snow cover to the U.S. as a whole. December 2010 precipitation in the contiguous U.S. was also near average, ranking 54th driest in the 116-year record. Montana and Utah had their wettest Decembers on record, and six other states had top-ten wettest Decembers--Minnesota, North Dakota, South Dakota, Oregon, Maine, and California. Six states had top-ten driest Decembers--Louisiana, Mississippi, Alabama, Arkansas, Kansas, and Delaware.
La Niña in the "moderate" to "strong" category
The equatorial Eastern Pacific Ocean is currently experiencing moderate to strong La Niña conditions. Sea surface temperatures (SSTs) over the tropical Eastern Pacific in the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region", were 1.5°C below average as of January 10, according to NOAA. The Australian Bureau of Meteorology put this number at 1.45°C below average (as of January 9.) Moderate La Niña conditions are defined as occurring when this number is 1.0°C - 1.5°C below average. Temperatures colder than 1.5°C below average qualify as strong La Niña conditions. NOAA is maintaining its La Niña advisory, and expects La Niña conditions to last through through spring.
Both El Niño and La Niña events have major impacts on regional and global weather patterns. La Niña typically causes warm, dry winters over the southern portion of the U.S., with cooler and wetter than average conditions over the Pacific Northwest. The Ohio and Mississippi Valleys states typically have wetter winters than usual during La Niña events.
December 2010 Arctic sea ice extent lowest on record
Northern Hemisphere sea ice extent in December 2010 was the lowest in the 31-year satellite record, according to the National Snow and Ice Data Center. Ice volume in December was also the lowest on record for this time of year, according to University of Washington Polar Ice Center. At the end of December, the eastern portion of Canada's Hudson Bay remained unfrozen, the first time in recorded history that Hudson Bay has not been completely frozen over at the end of the year. The unusual amount of open water led to temperatures that averaged 20°C (36°F) above normal over a region twice the size of Texas in this region during the first ten days of January.