NASA and the National Oceanic and Atmospheric (NOAA) have just released data showing that October 2009 was among the warmest Octobers on record, with parts of the U.S. among the few land masses cooler than normal.

According to data posted on 13 November 2009 by NASA's Goddard Institute for Space Studies (GISS), the combined global land-ocean temperature index for October 2009 was 0.66oC above the 1951-1980 base period. Tied with October 2003, it is the second warmest October on record (at least since 1880), behind only 2005 – which was 0.72oC above the mean temperature during the base period.  According to NASA data, the year 2005 went on to be the warmest year on record.

NOAA also posted separately developed data on 13 November indicating that the combined global land and ocean temperature anomaly was 0.57oC above the long term mean (1971-2000). That would make it the 6th warmest October in 130 years, and the 5th warmest year-to-date (January through October). 

Whether using NASA or NOAA data, it is very likely that 2009 will be one of the top ten warmest years on record, with nearly all of those years occurring during the last decade.

NOAA reported earlier in the week that October was the 3rd coolest for the U.S. (lower-48 states only); and that the year-to-date (January through October)  for the U.S. only was relatively normal.

While climate change denialists have seized on recent U.S. temperatures as evidence that climate change is not happening, not all parts of the U.S. have seen cool temperatures this year.  Alaska has been well above normal this year, continuing a long term warming trend; Florida too was above normal -- for the sixth month in a row, making it the 3rd warmest May-October on record. More importantly, the lower-48 states of the U.S. account for less than 2% of the globe.  What happens in the U.S. does not necessarily reflect what is happening over the other 98% of the planet.

It is the global situation and long-term trends that matter and these clearly show that that the planet overall was well above normal this year and this decade -- and that temperatures have been rising over the much longer term. 

For the straight dope on global temperature trends, read A warming pause? (6 October 2009) from RealClimate.org. It concludes:

"The bottom line is: the observed warming over the last decade is 100% consistent with the expected anthropogenic warming trend of 0.2 ºC per decade, superimposed with short-term natural variability. It is no different in this respect from the two decades before. And with an El Niño developing in the Pacific right now, we wouldn’t be surprised if more temperature records were to be broken over the coming year or so."

See also Do global temperature trends over the last decade falsify climate predictions? [PDF] from the UK Met Office.

Note that climate change is not just a matter of rising temperatures.  Those temperature changes drive other changes, including changes in atmospheric circulation (such as the jet stream) and changes in precipitation. 

Climate change denialists will find little comfort in the October precipitation data for the U.S.: it was the wettest October on record for the lower-48 states (see our posting, U.S. Sees Wettest October on Record; Arkansas Records are Washed Away, 9 Nov 2009). That's a record that goes back 115 years.

According to Global Climate Change Impacts in the United States (2009), a report from the U.S. Global Change Research Program, "[p]recipitation has increased an average of 5 percent over the past 50 years."  Furthermore, "[t]he amount of rain falling in the heaviest downpours has increased approximately 20 percent on average in the past century, and this trend is very likely to continue, with the largest increases in the wettest places."