December 2009: 4th or 8th warmest December on record

The globe recorded its eighth warmest December since record keeping began in 1880, and 2009 tied with 2006 as the fifth warmest year on record, according to NOAA's National Climatic Data Center. NASA's Goddard Institute for Space Studies rated December 2009 as the 4th warmest December on record, and the year 2009 tied with 2007 as the second warmest year on record. NOAA rated December 2009 ocean temperatures as the 2nd warmest on record, next to 1997, and land temperatures as the 31st warmest on record. The anomalously cool conditions over much of northern Asian and North American land areas may be associated with the near record December snow cover extent over Northern Hemisphere land areas--2nd most on record, behind 1985. Snow cover records go back to 1967. The December global satellite-measured temperatures for the lowest 8 km of the atmosphere were the 7th warmest on record, according to the University of Alabama Huntsville and RSS data sets.


Figure 1. Departure of temperature from average for December, 2009. Image credit: National Climatic Data Center.

One interesting note: the NASA global average temperature for 2009 was .57°C above average. NOAA's was .56°C above average. These temperatures were just .06°C below the all-time hottest year on record, 2005. The 11-year global sunspot cycle causes a variation of 0.1°C between the maximum and minimum of the solar cycle. We are currently at a deep minimum of the solar cycle, so we would have set a new global temperature record had we been at the maximum of the solar cycle. The other global temperature data set, the UK HadCRUT3 data, is not yet available for 2009. This data set is the one most often quoted by global warming skeptics, since it says that 1998 was the warmest year on record. However, HadCRUT3 fills in a huge area of missing data in the Arctic with the average temperature from the rest of the globe. This is bound to cause an underestimate of the global temperature, since the Arctic has warmed much more than the rest of the globe. The NASA and NOAA data sets fill in the missing data in the Arctic with data interpolated from the nearest stations in the Arctic, a procedure which is less likely to underestimate the global temperature.

December 2009: 14th coolest December on record for the U.S.
For the contiguous U.S., the average December temperature was 3.2°F below average, making it the 14th coolest December in the 115-year record, according to the National Climatic Data Center. The U.S. has been on quite a roller coaster of temperatures over the past three months--the nation recorded its third coldest October on record, followed by its third warmest November, followed by its 14th coolest December. The coolest December weather was in the Central U.S., where Nebraska had its eighth coolest December; Texas, Nevada, and Wyoming their ninth; and Montana and Utah their tenth coolest.

December 2009 was the 11th wettest December in U.S. history. It was a record wet month for Georgia, South Carolina, Virginia, and Maryland; 2nd wettest month on record for New Jersey; and the third wettest month on record for South Dakota, North Carolina, and Alabama. The Northwest U.S. was dry, with Washington experiencing its 11th driest December on record.

The year 2009: 35th warmest for the U.S.
For the entire year of 2009, it was the 35th warmest year in the contiguous U.S during the 115-year record. The coolest state was Nebraska, which had its 19th coolest year on record, and the warmest state was California, with its 16th warmest year on record. The driest state was Arizona, where 2009 ranked as the 4th driest year on record, while the wettest states were Illinois, Alabama, and Arkansas, who all had their 2nd wettest year on record.

U.S. tornado deaths: 2nd lowest on record
The year 2009 was below average for number of tornadoes, with a final tally around 1120 expected, compared to the 3-year average of 1297, according to the Storm Prediction Center. The 21 tornado deaths in 2009 was the 2nd lowest death toll in the 60-year record. Only 1986, with its 15 tornado deaths, saw fewer fatalities. The 60-year average annual death toll is 84.

U.S. drought
At the end of December, 6% of the contiguous United States was in severe-to-exceptional drought, which is well below average. The U.S. Drought Monitor shows no areas in the highest classification of drought--exceptional drought, and U.S. drought extent is close to its lowest value for the past ten years. The second highest category of drought, extreme drought, covers only a small region of northeast Arizona, and this will shrink over the remainder of January as much-needed rain falls across Arizona. About 43 percent of the contiguous United States had moderately-to-extremely wet conditions at the end of December, according to the Palmer Index (a well-known index that measures both drought intensity and wet spell intensity). This footprint is significantly larger than the long-term average.

Average U.S. fire activity in 2009
Significant fire activity occurred early in 2009, but wetter conditions across many parts of the nation as the year progressed, coupled with effective fire management, helped to restrain fire activity by mid-year. Despite the largest fire in Los Angeles County's (California) recorded history (Station fire), by the end of August the nationwide acreage burned by wildfire was very near the 2000 - 2009 average, and thereafter declined below average. Based upon data provided by the National Interagency Fire Center (NIFC), fire activity in 2009 ranked fifth highest (sixth lowest) out of the past decade in terms of number of fires, about 1 percent below the 2000 - 2008 average. Acres burned in 2009 were 14.5 percent below the 2000 - 2008 average, ranking seventh highest (fourth lowest) since 2000. Average fire size also ranked seventh highest out of the 2000 - 2009 period, at about 14 percent below average.

Strong El Niño conditions continue
Strong El Niño conditions continue over the tropical Eastern Pacific. Ocean temperatures in the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region", were at 1.6°C above average on January 10, just above the 1.5°C threshold for a strong El Niño, according to the Australian Bureau of Meteorology. The strength of El Niño has been roughly constant for the 9 weeks ending January 10. NOAA's Climate Prediction Center is maintaining an El Niño Advisory. Most of the El Niño models forecast that El Niño has peaked and will gradually weaken. Most of the models predict that El Niño conditions will last into early summer, but cross the threshold into neutral territory by the height of hurricane season.

December sea ice extent in the Arctic 4th lowest on record
December 2009 Northern Hemisphere sea ice extent was the 4th lowest since satellite measurements began in 1979 and slightly below December 2008 levels, according to the National Snow and Ice Data Center (NSIDC). Only 2005, 2006, and 2007 saw lower December arctic sea ice extent. The weather pattern over the Arctic in December 2009 featured a strongly negative Arctic Oscillation (AO). This pattern tends to slow the winds that typically flush large amounts of sea ice out of the Arctic between Greenland and Iceland. In this way, a negative AO could help retain some the second- and third-year ice through the winter, and potentially rebuild some of the older, multi-year ice that has been lost over the past few years. However, the AO has increased significantly in January, and it is unclear what the net effect of the AO on sea ice transported out of the Arctic this winter will be.

Next post
I'm at the 90th Annual Meeting of the American Meteorological Society in Atlanta, Georgia, and will be making my next post from Atlanta on Tuesday.

Jeff Masters