Professor Ian Plimer is one of the most influential global warming sceptics. A university academic in Australia, his trenchant views on climate change have helped persuade opposition politicians in his home country to back away from supporting schemes to reduce emissions. His book Heaven and Earth: Global Warming: The Missing Science (reviewed here last month) remains a best-seller in the UK.

He spoke in central London on 1 December at a meeting organized by the anti-EU United Kingdom Independence Party (UKIP). The material in the talk was largely taken from his book, though his language was even more open and unrestrained. Unsurprisingly, in view of the controversy over the content of recently exposed CRU emails, he repeatedly used the word 'fraud' or 'fraudulent' to characterize the views of his opponents. He described his critics as 'rent-seekers' who spent their time seeking out the next research grant.

This article takes a small number of the more controversial statements made by Professor Plimer and sets them against the standard scientific view.

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The role of CO2 in climate change The burning of fossil fuels and the cutting down of forests adds to CO2 in the atmosphere. Carbon dioxide acts as a blanket, assisting the world's atmosphere in retaining heat. More CO2 means more heat retention, say the textbooks. If we continue adding global warming gases, global temperatures will rise.

Does Plimer agree with this? During the talk he said that 'doubling CO2 would have very little effect on temperature'. Higher CO2 levels in the future would have 'negligible' impact. At another time he said it would have absolutely no effect.

In a brief chat after the speech, I asked the professor to be more specific. What was his estimate of the impact so far on global temperatures of the CO2 mankind has added to the atmosphere? '0.1 to 0.3 degrees' (Celsius) was his response. The conventional scientific answer to this question might be about three times this figure.

Professor Plimer went on to say that his figures are lower than the IPCC estimates because the standard science is wrong about the absorption of CO2 in natural sinks such as the oceans. The typical residence time of carbon dioxide in the atmosphere is seven or eight years, he said. This is a much, much lower figure than proposed by conventional science. The standard view, sometimes called the Bern Carbon Cycle model, sees some of a pulse of new CO2 being removed rapidly from the atmosphere but also suggests that a portion remains for hundreds of years.

I responded to Professor Plimer's remark by asking how his views on the rapid absorption of CO2 by natural sinks could be compatible with the observed yearly growth in the atmospheric concentrations of the gas since the beginning of the industrial revolution. In 1800, CO2 accounted for about 280 parts per million of the global atmosphere. Since then, concentrations have risen to nearly 390 ppm. CO2 arising from fossil fuel combustion has a different mix of carbon isotopes to the existing ambient gas. From many analyses using this and other parts of science we know that approximately half the CO2 added to the atmosphere by man is still there. (In the body of his talk the professor asserted that the assessment of how much fossil fuel CO2 is entering the atmosphere comes from a 'dodgy calculation' and he does not accept isotope analysis as a way of determining the source of carbon dioxide.) I wanted to understand how Plimer's views on the short life of CO2 in the atmosphere could be made consistent with the rate of rise of observed CO2 levels since industrialization began.

He answered by saying that science was wrong to assume that the pre-industrial atmosphere held 280 parts per million of CO2. It was actually much higher, he said. The net addition to global CO2 levels by the burning of fossil fuel is therefore implicitly substantially lower than science suggests. Plimer says that measuring techniques are inadequate and that proper measurement would show that nineteenth- and early-twentieth-century CO2 levels were much higher than is assumed and very much more variable. He said to me that the belching of carbon dioxide by volcanoes would, for example, have produced short-lived but large rises in greenhouse gas concentrations. The charts that show stable atmospheric concentrations prior to the industrial revolution are therefore wrong, Plimer said.

In the body of the talk Professor Plimer attacked the quality of even today's Mauna Loa data. He said that the measurement techniques were flawed and that the nearby volcano emits considerable amounts of CO2 which affects the quality of the record. 86% of all the observations were rejected, he said, and only data that accorded with the scientists' prejudices was used. The professor did not, however, mention that many other sites around the world also measure CO2 concentrations and all of these stations report the same trend. (Absolute levels are different, inter alia, because of seasonal variations in CO2 concentration in different parts of the world resulting from plant growth.)

In the space of a short conversation, Professor Plimer attacked the foundations of climate science. He said that we overestimate the impact of CO2 on climate, that carbon dioxide is absorbed by sinks very rapidly, and, finally, that the standard measures of greenhouse gas levels over the last two hundred years are substantially in error, both now and in the past. In other words, almost everything that mainstream science believes about carbon dioxide in the atmosphere is incorrect. Fifty years' work from scientists working independently all over the world on these issues has been misdirected, flawed, biased, and ignorant.

The assertion that scientists have systematically understated CO2 levels before the industrial revolution is particularly striking. To my knowledge, no one else has ever recently suggested that the stable pre-industrial level of 280 ppm is substantially inaccurate. The sources of this figure, such as measurements from the air trapped in ice cores, are usually considered to provide robust information. The number of scientists in the world who accept Professor Plimer's views on this issue is vanishingly small. As far as I know, none of the other leading sceptics agree with him on this issue.

But he has to believe that the standard charts are wrong, even if this makes him even more at odds with the scientific establishment on this issue than other sceptics. If CO2 has risen by over 100 ppm in the last couple of centuries, he would have to accept that the gas has a much longer residence time in the atmosphere than he hypothesizes. And this would be incompatible with his view that CO2 is only responsible for '0.1 to 0.3' degrees of the rise in temperature since large-scale burning of fossil fuels began.

However, Professor Plimer had not even been consistent about whether world temperatures had risen at all. At some points in the body of his talk, he said that levels were rising, but this is 'normal'. At other points, he said it was falling or stable. At yet other moments, he acknowledged some regional warming but said that large areas of the globe were getting colder. I believe that a dispassionate observer listening to Professor Plimer would have struggled to understand what he really believed about temperature rises, absolute CO2 levels or, most importantly, the effect of CO2 levels on temperature.

Nevertheless, he railed strongly against the theoreticians and the careful scientists who work on climate change. His principal charge was that they never go out into the real world to make their own observations. He said that they were 'people in basements' running computer models to appeal to their political masters and that only the sceptics were real scientists. Conventional science and its models made you 'bang your head with boredom'. By contrast, he said that his thoughts on climate change provided a 'far more evocative and sensual' story and are therefore more likely to be right than conventional science. [ad#Plimer-Amazon]