Man-made Global Warming in Doubt

Below are portions of one of those hacked emails from Climate Research Unit at the University of East Anglia. The email dated October 1996 is from an environmental writer Fred Pearce to climate researcher Briffa Keith: 

For climatologists, the search for an irrefutable "sign" of anthropogenic warming has assumed an almost Biblical intensity. The leading figures of the UN's Intergovernmental Panel on Climate Change (IPCC), claim that, in all probability, they have seen it. Last summer [ed: 1996], the IPCC's scientific working group, chaired by former UK Meteorological Office boss Sir John Houghton, concluded that "the balance of evidence suggests a discernible human influence on global climate". But it is like the "balance of evidence" suggesting BSE causes CJD. The judgment is far from "beyond reasonable doubt". The case remains "not proven".

Few investigators doubt that the world has warmed recently. Nor that the enhanced "greenhouse effect" of pollution from gases such as carbon dioxide, will warm the planet. But in the past five years, climate researchers have growing increasingly aware of how little they really know about the natural variability from which they must pick out the "signal" of human influence.

The models' error was not, perhaps, too surprising. As Barnett points out, they do not include vital "forcing" mechanisms that alter temperature, such as solar cycles and volcanic eruptions. Nor can they yet mimic the strength of the largest year-on-year variability in the natural system, the El Nino oscillation in the Pacific Ocean, which has a global impact on climate.

Nonetheless, the findings should serve as a warning, Barnett says, that "the current models cannot be used in rigorous tests for anthropogenic signals in the real world". If they are they "might lead us to believe that an anthropogenic signal had been found when, in fact, that may not be the case."