Official predictions of man-made global warming may have mistaken cause and effect, according to scientists sceptical of a link with fossil-fuel burning.
Global temperatures may be rising naturally, and as a consequence increasing the carbon dioxide in the atmosphere, rather than man-made production of this greenhouse gas being the cause of global warming and increasing temperatures, according to Jack Barrett, of the department of chemistry at Imperial College in London.
The Inter-governmental Panel on Climate Change (IPCC) which, as reported in yesterday's Independent, has now agreed that man-made global warming is under way, may be putting the cart before the horse, Dr Barrett said. He cast doubt on official predictions that the concentrations of carbon dioxide could double. "I don't believe it can or will happen," he said.
Dr Barrett believes that the oceans will act as a "sink" for the gas, which will dissolve in seawater and thus be cleared from the atmosphere. He said that the predictions by the IPCC of up to a 3.5C rise in temperatures over the next century were "unimpressive, because they come up with numbers which are less than the overall uncertainties in the quantities they are trying to predict".
The criticism of the IPCC was taken up by Richard Lindzen, professor of meteorology at Massachusetts Institute of Technology. The IPCC produces "waffle statements which don't say anything, which nobody can disagree with", he said. Science was resorting in a "very unseemly" manner to the language of the advertising industry, Prof Lindzen maintained. "I think in the long run the IPCC statement will be an embarrassment to the scientific community." By that time, however, he said, the leaders of the IPCC would long since have gone into retirement.
The warming of the global climate over the past century has been completely within the range of natural variability, Prof Lindzen said: "The climate is changeable."
The IPCC had got agreement between its computer models and the actual behaviour of the climate only by including the effect of aerosols in the atmosphere, he said. But the panel had included "an arbitrary amount of aerosols", and so it was not surprising that it had obtained the correlation.
Prof Lindzen pointed out that the major part of the warming took place before 1940, before most of the fossil-fuel burning had taken place and therefore before the major portion of the carbon dioxide had been released into the atmosphere. Between 1940 and 1960 the global climate actually cooled slightly, before warming again to the late 1970s.
Yet since 1979, there has been no net increase in the average global temperature, Prof Lindzen said. "The net trend has been insignificant, but the IPCC would have predicted at least half a degree increase."
Dr Barrett also says there is no experimental evidence for anything that could be ascribed to man-made effects. But he also takes issue with the fundamental conceptual approach underlying the climatic models of the IPCC. The panel, he says, has underestimated the extent to which the oceans would naturally absorb carbon dioxide, and eventually it could be converted to limestone. He also believes that the panel is mistaken about the length of time the gas lingers in the atmosphere. On average, the gas can only remain in the air for about seven years whereas "the IPCC says decades to hundreds of years".