SIR – I would like to correct the record following Philip Bird’s letter of November 26.

The difference between the average temperatures of the 1930s and 1950s is not statistically significant. The conclusion should instead be that they were very similar.

The 1950s were cooler than the trend because the cooling effect of the smoke, soot, ash, dust and sulphur dioxide we were putting into the atmosphere exceeded the warming effect of the extra carbon dioxide and other greenhouse gases (remember acid rain and the Clean Air Act?).

The IPCC does verify the data from the Goddard Institute for Space Studies indirectly, and its Fourth Assessment Report states that warming rates from balloon and satellite observations were similar to those of the surface temperature record.

NASA reports that the Arctic ice minimum for 2008 was the second-lowest amount recorded since the dawn of the satellite era (2007 was the lowest). To say that it is increasing is clutching at straws.

If the implication of Mr Bird’s comment about GISS supplying incorrect data (easily detected and rectified) is that an administrative slip destroys all credibility, you would think that he would give my correct name.

Ron Harding, Oakwood Drive, Bingley