President’s Column, March 2010
Mon, Mar 22 2010

Global warming continues I have been looking at the global temperature record, as measured by satellite and surface data. I have plotted the time series of six-month (September-February) global mean temperature anomalies in the figure below. The data I have used are the Spencer-Christy lower tropospheric temperatures from satellites (labelled “UAH” in the figure) and the surface temperature data from the NASA Goddard Institute for Space Studies (labelled “GISS”). Both data sets are readily available (UAH from http://vortex.nsstc.uah.edu/data/msu/t2lt/uahncdc.lt; GISS from http://data.giss.nasa.gov/gistemp/tabledata/GLB.Ts+dSST.txt). Both data sets are of anomalies from the period 1979/80-1998/99, ie the first twenty years of the satellite observations. The GISS data originally used a different base period, so I have recalculated the GISS time-series with the same base period as the UAH data. Please look at the data, re-do the analysis, and see if you come to similar conclusions to those I describe below. 

The last six months (September 2009 – February 2010) have been the warmest September-February observed in the satellite record, by a large margin. In the GISS surface data the last six months are the equal warmest September-February on record (equal with 2007/08). Eyeballing the graphs of the surface and satellite temperature record should convince anyone that global warming continues unabated. Fitting a linear trend to the data since the start of the satellite observations produce virtually identical trends in the two data sets. Even the interannual variations in the two temperature series are close matches.

A corollary of this close match between the surface and satellite variations and trends is that the surface warming trend is NOT due to the urban heat island effect. Nor is it due to decreases in the numbers of stations used in the surface analysis. Neither of these problems would affect the satellite data. Furthermore, the trend is not just due to a year or two of extreme temperatures – the very warm years (often associated with an El Niño) are progressively getting hotter, as are the cool years (which are often associated with a La Niña). Another corollary is that the GISS data provide a very credible analysis of variations and changes in global mean temperature (since they match the satellite observations), supporting the conclusion that the 21st century has seen the warmest September-February periods for at least 130 years.

As I write this column (15 March) the Spencer-Christy satellite data for March 2010 are running well above the previous record for March (set in 2004). November 2009 was the hottest November in their data and January 2010 was the hottest January, with February 2010 coming in as the second hottest February. It doesn’t look like the run of record hot global temperatures will stop anytime soon.

Neville Nicholls March 2010