Steven Sherwood
Steven Sherwood is director of the Climate Change Research Centre at the University of New South Wales.
In February, the Australian Academy of Sciences presented an update of their five-year old document “Climate Change: Questions and Answers,” to explain the scientific community’s understanding of global warming. But already at least one academy member has publicly criticised the document as "cherry picking" the data.
Hostile reactions from tiny, vocal minorities have similarly plagued the dozens of other prestigious scientific societies overseas that have issued explainers or position statements on climate change. Are scientific societies overreaching by trying to summarise a contentious topic? Or are contrary voices being squashed?
Debate on any subject must build on a foundation of agreed fact. Unfortunately, even propositions about climate that are accepted by every relevant expert are often questioned in the media. Examples include that carbon dioxide in the atmosphere exerts a warming effect because it traps infrared light, or lowers ocean pH, or is accumulating in the atmosphere because of human activities, or that the models for making detailed predictions are imperfect. This constant questioning is one reason why authoritative summaries are so important. One cannot have a meaningful debate on public finances if, say, one does not accept the laws of arithmetic or know the details of the current Budget.
Less straightforward questions about climate change have been debated for decades, mostly out of public view, in what is now a vast and complex scientific literature. This literature is the basis for documents such as the Academy’s Q&A. Contrarians have as much opportunity as anyone to contribute to it.
The reason the contrarians have not held greater sway in assessments of the science by expert bodies is that their arguments don’t survive serious scrutiny against the broader evidence. For example, the contention that climatic changes during the “medieval warm period” were similar to those seen today seems true if one looks only at a few local records, as often happened in the old days. But newer meta-analyses of data from all over the world now demonstrate that 20th century warming is unique. It is not only happening in parts of the Northern hemisphere. It is global.
Contrarians further pretend that if models are oversensitive this would leave the scientific "consensus" in tatters.
Another example is the contention that, because most climate models overestimated warming during the last 20 years or so, they must be “over-sensitive”, in other words exaggerating the warming effect of CO2. Again this may seem reasonable at first blush, yet quantitative analysis of a full range of possibilities shows that the exact rate of warming during recent decades is a poor indicator of the future, in much the same way as recent stock returns can be a poor indicator of long-term performance. A more balanced assessment weighs such bits of evidence against many others, some of which suggest that most models underestimate the warming effect of CO2.
Contrarians further pretend that if models are oversensitive this would leave the scientific "consensus" in tatters. In fact, even a halving of best-guess climate CO2-sensitivity, although it would be great news and make the situation less dire, would have little impact on any conclusion stated in the Academy document. Unmitigated emissions would still lead to warming and ocean acidification at rates likely unprecedented for millions of years – the warming would just take a few more decades.
In the media it can appear that if even one or two scientists disagree with a “consensus" then the science can be dismissed as half-baked. But history and psychological research show otherwise. When the questions asked by science become politicised or connected to a world-view, people tend to use evidence only to confirm their previously held views and become resistant to change. Practicing scientists may be less vulnerable because our work involves testing our hypotheses against the results of experiments and constantly defending our conclusions against challenges from colleagues. On the other hand, we love to argue, and (in some cases) grab attention. Unanimous agreement on politicised questions is therefore never going to happen, no matter how unequivocal the case becomes.
Indeed history reveals apparent dissent against nearly every scientific consensus that became politicised or affected some interest group. Into the 20th century one could still find a few scientists denying that cigarettes caused cancer. There also remained prominent deniers of the dangers of lead and asbestos, Einstein's theory of relativity, and of the chlorofluorocarbon-induced ozone hole, long after legitimate reasons for doubt had evaporated.
Science marches on unaffected by assessments carried out by scientific bodies. A declaration that nearly every expert has concluded that “X is correct”, will not deter a scientist from trying to prove that Y is correct – nor should it. This is the life blood of science. But if repeated attempts to find evidence for Y have failed so far, the public needs to know this, and must act according to the evidence as it stands.
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