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Jul 18 2010

Mid-Year Update on Global Temperatures

NOAA’s National Climatic Data Center (NCDC) have announced that the Earth has just experienced its warmest June on record, 0.68°C warmer than the 20th-century June average of 15.5°C. Most of the globe was warmer than usual, with the highest temperature anomalies seen in eastern and western Asia, eastern North America, western South America, and most of the Atlantic Ocean. The only surface temperatures much cooler than average were in the eastern Pacific and Southern Oceans. The warmest June is particularly notable in that it follows the warmest March, April, and May.

(Global temperatures are usually given as anomalies relative to a 20th century average because they are easier and more useful to compare than absolute temperatures. The last month with a temperature below average was February 1985.)

Let’s quickly recap the year so far. It began with an unusually cold winter in northern land areas, related to the Arctic Oscillation (AO), which in February 2010 was at its most negative value on record, moving heat to Arctic regions. Despite the unfortunate and disproportionate impact this had on public opinion, January was a relatively warm month globally, and the Southern Hemisphere had its warmest February on record.

While conservative commentators chattered about the cold winter, the global temperature soared. At a whopping 0.77°C above the March average of 12.7°C, March 2010 was not only the warmest March globally, but also the (seasonally adjusted) third warmest month of all time, after February 1998 and January 2007. April 2010 came in at 0.73°C above the April average 13.7°C, and May 2010 was 0.68°C above the May average 14.8°C.

The last four months have not only each been the warmest for their respective month, but all these months were also among the top 20 monthly anomalies of all time. (Currently April is sixth, May is 16th, and June is 15th.)

Global temperature has remained relatively high despite the recent end of El Niño. As the eastern Pacific continues to cool, La Niña conditions are expected to develop during the southern winter (which, incidentally, would mean wetter weather in Australia). It will be interesting to see if this causes a dramatic drop in global temperature.

In a previous post I compared the record-warm beginning of 2010 to the then-record-warm beginning of 2007 — in the case of 2007, the onset of La Niña caused the Earth to cool rapidly, and I thought this might be an analogue for the current situation. However, comparing the global temperature anomalies for the first half of each year, already we see that this year is already running considerably hotter (0.68°C for January-June 2010 versus 0.60°C for 2007).

Also, the 12-month mean global temperature continues to climb. July 2009 – June 2010 was the third warmest 12-month period in the NCDC record, at 0.63°C above the annual average 13.9°C. The two warmest are the 12-month periods ending in August 1998 and September 1998 (0.64°C and 0.63°C respectively). For July 2010 to break that record, the global monthly anomaly would have to be greater than 0.66°C.

All these numbers come from NCDC, so keep in mind that there are slight differences with other global temperature records such as the one maintained by Goddard Institute for Space Studies (GISS). Probably the most notable difference for 2010 is that according to GISS, the 12-month mean record has already been broken. But for the sake of consistency I’ll continue to report the NCDC results in future updates.

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