May 28, 2008

experts react to research on global temperature records as published in Nature

Researchers analysed data sets of Earth surface temperature from throughput the twentieth century, and concluded that the cooling period observed in the middle of the century may have been largely a result of the methods of measurement used, rather than natural climate cooling processes.

Dr Tim Palmer, Head of Research Division, European Centre for Medium-Range Weather Forecasts, Reading, said:

“Our Earth has been warming over the last hundred years, and scientists believe that the principal cause is anthropogenic emissions of greenhouse gases. However, the observed global-mean temperature record does not show uniform warming. Part of the year to year variability in temperature can be linked to natural climate fluctuations such as associated with the El Nino event. Others, particularly associated with the cooling in immediate post-WW2 years may arise from pollution associated with sulphate aerosols. However, there has always been some uncertainty in whether the aerosol explanation can account for all of the post-WW2 temperature drop, much of which was indeed quite sudden.

“The authors have identified an additional factor for this sudden drop in global temperature around 1945. It is totally artificial and arises because the fraction of US to UK- based ships taking sea temperature measurements changed suddenly after the war. In those days, the method by which sea temperature was measured depended on the country of origin of the ship.

“The paper shows how difficult it is to produce fully reliable historical estimates of global mean surface temperature. Tiny biases due to the measurement method need to be identified and taken into account. Nevertheless, by identifying a new source of bias, the paper gives further support that main trends in 20th Century temperature are anthropogenic in origin.”

Prof. Mike Hulme, School of Environmental Sciences, University of East Anglia, said:

“The paper in Nature by Thompson et al. (29 May 2008) is a good example of the value of continuous and critical re-evaluation and testing of ideas, theories and data in science. The authors discover an anomalous and rapid drop in late 1945 of the global-mean sea surface temperature record and ask why was this so? They provide a convincing explanation related to the way sea surface temperature measurements were made at the time and later corrected.

“The paper should also raise the question why such an important discontinuity in this iconic index of global warming was not spotted earlier and appropriate corrections made. The answer to this question lies in observing and understanding the practices of scientific knowledge creation and the social and institutional contexts in which science operates. This new study by Thompson et al. doesn’t erode our belief that the world is getting warmer. It does tell us, however, that science loses its unique claims to valid knowledge if challenge, scrutiny and dissent are ever lost from its operating norms in favour of a cosy and unquestioning consensus.”