The Australian,

30th April 2008


While acknowledging that various temporary influences have brought some very brief periods of cooling since 1973, David Karoly ("Warming trend has not been reversed", 29/4) quotes the International Panel on Climate Change's conclusion that warming over the past 100 years is "unequivocal" and asserts that most of the increase reflects increased greenhouse gas emissions.


However, although the average global temperature recorded by surface measurement is higher now than 100 years ago, there was an extended cool period from 1940 to 1975 despite large increases in emissions then. There is no agreement that this cooling reflected aerosols. There is also dispute as to whether (higher) surface temperature measurements are more accurate than other (lower) measurements. Recent research suggesting surface measurements have considerably understated urban heating effects add weight to doubts as to the accuracy of the former. Further, we now have a period since 2001 of little temperature change, again despite increased emissions.


Professor Karoly also fails to mention the acknowledgement within all IPCC reports of the validity of the analysis showing that increased concentrations of CO2 in the atmosphere have a progressively diminishing effect on temperature. This important analysis suggests even a doubling of concentrations between now and 2100 would increase temperatures by only 0.3 degree. Why did the IPCC ignore this in compiling its conclusions?


In short, it's not surprising the IPCC's conclusions on both past and projected warming are increasingly questioned by a growing number of expert scientists and others. An independent inquiry is needed into climate science and its uncertainties.