Professor Don Aitkin’s sceptical view of global warming, presented (PDF 258KB) to the Planning Institute of Australia on April 2, 2008, has been widely publicised. He claims that the current level of warming is not historically unprecedented, that the link between warming and greenhouse gas emissions is weak, and that we should not do anything to restrict emissions until it is “absolutely plain” that there is no alternative. He says the global warming issue is a distraction from the water and peak oil crises facing Australia.
Having failed to understand why climate scientists are advocating urgent action (“stridently”, he claims), Professor Aitkin proceeds to play the people instead of the ball by questioning their motives, claiming, among other things, that having set up the IPCC the scientists have to keep justifying it by claiming there is warming.
Professor Aitkin poses several questions, the three most immediate being whether the Earth is warming, whether its present warming is unprecedented, and whether our burning of fossil fuels is causing the present warming. However there are other equally important questions lurking behind this debate, such as whether it would really be so hard for us to change our lifestyle, whether such changes would have other benefits, and whether we must change anyway, for reasons other than global warming.
Professor Aitkin makes much of the uncertainty of climate observations, and claims scientists don’t discuss them, particularly singling out the IPCC. In this he misunderstands or misconstrues the role of the IPCC reports: they are entitled “Assessment” reports. They are not just the science, they are an assessment of the science, using a process I will explain more later. Evidently he denies IPCC the role (I would say the responsibility) of assessing the state of the evidence. Nor does he note its consensus procedure and the political vetting of its final texts, both of which tend strongly to make its assessments conservative.
Professor Aitkin presents himself, on the other hand, as a paragon of disinterested enquiry. However, he inevitably makes his own selections and judgments of the evidence. For example, he queries the claim that the present warming is unprecedented and cites one study arguing the Medieval Warm Period in Europe was warmer than at present. However, a number of temperature proxies show the temperature to have been 0.0-0.3C cooler than the mid-20th century (and thus 0.6-0.9C cooler than now - you can see the graph on Wikipedia). Also, according to the US National Oceanic and Atmospheric Administration there is no clear evidence that the warm period extended outside Europe.
More egregiously, Professor Aitkin makes no significant mention of dramatic changes in the Arctic, or of pervasive and rapid retreats of mountain glaciers. These are noted only as “the evident melting of sea ice and the retreat of some glaciers”. In this statement he misrepresents the observations of mountain glaciers, which are indisputable, and glosses over perhaps the most dramatic and disturbing symptom of warming.
Professor Aitkin claims there is no reasonable evidence that greenhouse gas emissions are the cause of the present warming (though he acknowledges well-established basic physics). One of his arguments is that there is “no dramatically linear relationship” between the two during the 20th century. But of course there are natural short-term fluctuations in temperature (which sceptics like to emphasise) but not in the rise of carbon dioxide, so we don’t expect any simple linear relationship, particularly in the short term. This is a superficial and uncompelling argument.
Another argument, frequently raised by sceptics, is that during the ice ages temperature rises preceded carbon dioxide rises. Professor Aitkin leaves the implication dangling that we don’t understand why, and that this also shows that carbon dioxide levels do not determine temperature.
In fact this topic is well (if not widely) understood. The ice age fluctuations were triggered by fluctuations in the amount of heat received from the sun (due to slow gyrations of Earth in its orbit around the sun), but the temperature fluctuations would have been minor were they not strongly amplified by the carbon dioxide released as temperature rose. The amplification also explains the strongly asymmetric temperature fluctuations (slow cooling, rapid warming). The conclusion is that carbon dioxide was the dominant factor, though not the trigger. The ice age observations thus strongly support the hypothesis that a rise in carbon dioxide levels causes a rise in temperature.
Our present situation is different from the ice age situations. Solar heating has not changed significantly, but carbon dioxide levels have gone up a lot - higher than they’ve been for at least three million years. Our understanding of the ice age fluctuations gives us strong reason to expect that temperatures will increase, with a time lag of a few decades. The fact that the mean temperature has increased by at least 0.6C over the past few decades (a conclusion Professor Aitkin does not dispute) is then reason for serious concern.
There is additional, longer-term geological evidence in which carbon dioxide levels correlate well with surface temperature. The implied temperature variation is, if anything, greater than computer climate models suggest. Thus, contrary to Professor Aitkin’s claim, there is independent and strong evidence that greenhouse gases cause warming. Climate models, for all their imperfections, confirm this, which is one reason to take them seriously, if cautiously.
Professor Aitkin asserts that “there is simply no evidence” that polar ice will melt and that sea levels will rise. The only citation he makes is to a claim that recent evidence may show a slight cooling of the oceans during the past five years. Even if substantiated, that would be no basis for his grand assertion.
He fails to mention clear evidence of the acceleration of both melting and ice movement in Greenland. There is also clear geological evidence for polar melting and sea level rise accompanying higher temperatures.
Three million years ago, when the Earth was 2-3C hotter, sea levels were 15-35m higher. This is roughly consistent with evidence from the last glacial maximum and from a warm period 40 million years ago that about 20m of sea level change occurs for each degree of temperature change.
We are likely to experience at least 2C of warming. The complete melting of the Greenland and West Antarctic ice sheets would contribute about 7m each to sea level, so evidently even more ice was lost three million years ago under not dissimilar conditions. Professor Aitkin’s discussion of potential sea level rise is quite deficient.
Professor Aitkin queries computer climate models at some length. They are indeed still significantly limited, and their results must be treated with care. However our conclusions about global warming do not rest solely on computer models, as the preceding discussion will have made clear.
Professor Aitkin reveals his superficial understanding by claiming that if they can’t make a reliable 24-hour forecast then one shouldn’t believe long-term climate forecasts. He evidently lacks the elementary understanding that weather causes erratic fluctuations around a relatively slowly changing mean, and that climate is about the long-term means.
He also suggests their climate forecasts would be more believable if they would forecast the climate for 2009. However climate scientists repeatedly emphasise that one can’t reach conclusions about global warming from a single year’s record, nor even from trends over a few years, one has to look at longer-term trends.
Having failed to appreciate some of the key arguments supporting the global warming hypothesis, Professor Aitkin turns his attention to explaining to himself why climate scientists persist in making urgent pleas to curb greenhouse gas emissions.
He suggests they are protecting their turf, reputations and pet idea, and revelling in the extra funding and influence they are receiving. He describes the more activist scientists, and environmentalists in general, as holding a “quasi-religious” view. He says The Greens, “greens” and environmentalists welcome and propagate the global warming view because it fits their own perceptions (implying that those people have no rational basis for their views). He says even democratic governments like to have issues to scare people with. (Well yes, we’ve certainly seen the terrorism threat used that way, but I struggle to think of a government that has yet turned to global warming to scare its citizens, as all of them have had to be dragged kicking and screaming to acknowledge the problem.) He says people have an appetite for horror stories, and the media love to play to that (no argument there, but the media don’t care which story they peddle).
There are quite a few things one could say about these characterisations, only a couple of which will be noted here. Sceptics love to claim climate scientists are only in it for the research funding, ego tripping, alleged influence and so on, but they rarely mention the trillions of dollars and dominating global influence that fossil fuel industries have at stake, and that ExxonMobil, in particular, actively protects. Professor Aitkin laments that he has been called a “denialist” by others, yet he labels climate scientists as quasi-religious and with the several other descriptions just mentioned.
Scientists are human, and scientific debates fall short of the ideal. There is turf protection and self-promotion, and rancour are not uncommon. As an advocate of a minority view in my own field for 20 years, a view ultimately vindicated, I am personally acquainted with these imperfections. The IPCC process is specifically intended to step back from the front-line disputes to see what scientists can agree on. This is the part of the IPCC process that seems to have completely escaped Professor Aitkin’s understanding.
Even so, not everybody ends up satisfied with its assessments. Many, me included, feel it is too conservative. However in reaching for the conspiracy theory favoured by sceptics and denialists, to make up for his own deficient understanding, Professor Aitkin besmirches a great many excellent and conscientious scientists.
Professor Aitkin makes belated acknowledgement in his speech of the precautionary principle, which is basically that we would be wise take some preventative action as insurance against potential catastrophe.
His view seems to be, as best I can understand it, that there may be many possible reasons for climate change, so we’d be foolish to assume we’ve identified the real culprit and should therefore just accept and adapt to whatever comes to pass. When I reminded him in correspondence that to act effectively to avert global warming we know we must act before there is certainty, because of the time lags in the climate system, he said that my argument for the insurance policy view would only apply if the climate scientists are certainly correct. I don’t pretend to understand the logic of these statements.
Professor Aitkin considers global warming to be a distraction from more immediate crises, such as water and peak oil. However sensible action would mitigate all three crises, and others besides, including declining soils, rivers, forests, fisheries and coral reefs, and pervasive chemical pollution. These are all symptoms of our over-exploitation of the Earth, which we must reduce anyway, regardless of global warming. It is not widely appreciated how relatively easy it is to reduce our wasteful use of energy and other resources. Much wastage can be eliminated at a profit, and much more for modest cost and with multiple spin-off benefits.
The signs of global warming have recently accelerated. Most notably, melting of Arctic sea ice has dramatically accelerated since 2005, and there are sensible reasons to fear that it could be the first big domino - in a chain reaction of tipping dominos - that could shift us irreversibly into a much more hostile climate, which would certainly threaten the viability of our global industrial civilisation. (The signs of accelerated warming and the low costs of mitigation are discussed more fully in the full version of this article (PDF 44KB).)
With the signs ever more threatening, with other compelling reasons for action, and with the cost of action modest, there is no reason at all to delay action on global warming.
This is an edited version of a longer article, the full version of which is available here (PDF 44KB).