Another skirmish has broken out in the long-running battle between climate scientists and so-called sceptics, with the hacking of email messages between some of the world's leading researchers on global temperature trends. But as usually happens in the blogosphere, this episode is generating more heat than light and is likely to lead to more public confusion over the causes of climate change.
For the past few years, a small group of climate change 'sceptics' have been poring over scientific journal papers that report historical trends in temperatures from around the world, as recorded by directly by thermometers and other instruments, and by 'proxies', such as tree rings. Their primary objective has been to seek out evidence that global warming has been invented by climate researchers who fake their data.
Among their main targets have been papers published by research teams led by Michael Mann at Pennsylvania State University and Phil Jones at the University of East Anglia, and particularly those featuring the famous 'hockey stick' graph, showing that average temperature in the northern hemisphere was relatively stable and constant for most of the last couple of millennia, but rose dramatically upwards in the last 100 years. This graph appeared prominently in the landmark Third Assessment Report from the Intergovernmental Panel on Climate Change in 2001, which concluded that "most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations".
The attacks on the hockey stick graph led the United States National Academy of Sciences to carry out an investigation, concluding in 2006 that although there had been no improper conduct by the researchers, they may have expressed higher levels of confidence in their main conclusions than was warranted by the evidence.
The 'sceptics' believe they have been vindicated and have presented the hockey stick graph as proof that global warming is not occurring. In doing so, they have ignored the academy's other conclusion that "surface temperature reconstructions for periods prior to the industrial era are only one of multiple lines of evidence supporting the conclusion that climatic warming is occurring in response to human activities, and they are not the primary evidence".
More importantly, these skeptics have not overturned the well-established basic physics of the greenhouse effect, namely that carbon dioxide is a greenhouse gas and increasing its concentration in the atmosphere causes the earth to warm. They also have not managed to make melting glaciers and rising sea levels, or any other evidence of warming, disappear into thin air. But they have managed to confuse some of the public about the causes of climate change.
Over the past five years, Mann and Jones in particular have been subjected not only to legitimate scrutiny by other researchers, but also to a co-ordinated campaign of personal attacks on their reputation by 'sceptics'. If the hacked e-mails are genuine, they only show that climate researchers are human, and that they speak badly in private about 'sceptics' who accuse them of fraud.
It is inevitable as we approach the crucial meeting in conference in Copenhagen in December that the sceptics would try some stunt to try to undermine a global agreement on climate change. There is no smoking gun, but just a lot of smoke without fire.