Sawyer's succinct summary of the climate change science understood at that time can be compared with the four volumes of the IPCC Fourth Assessment on Climate Change being released through 2007. The IPCC assessment involves more than 400 authors, about 2500 reviewers, and runs to several thousand pages with many thousands of references. Such a comparison shows that much has been done to address the concerns and uncertainties expressed by Sawyer at the time. He was concerned that the rudimentary understanding of cloud processes and other climate system feedback resulted in uncertainties regarding predictions of warming. At the time, climate models were in their infancy, but Sawyer saw them as the best way to examine this feedback and reduce the uncertainties in climate change predictions. Since then, models have improved substantially and now include many more processes in more detail than was possible in the early 1970s, and the various climate processes that may enhance or offset the effects of carbon dioxide have been studied in detail.
Despite these advances, our best estimate of the warming to be expected from a doubling of atmospheric carbon dioxide concentration has changed little from Sawyer's time. Our best estimate of the temperature increase that would result from a 25 per cent increase in atmospheric carbon dioxide concentrations is still around 0.6 degrees. The scientific consensus of Sawyer's time was very similar to the scientific consensus in 2007.
Of course, better climate models and improved data and analyses have allowed the IPCC to discuss and even project possible changes in many other meteorological variables than could Sawyer, including extreme weather of various kinds as well as sea-level. The IPCC now also looks in detail at regional aspects of climate View More »