Most of all, global-warming sceptics delight in highlighting scientific uncertainty. Climate models, they say, are oversimplifications of physical processes, meaning that we can’t know how accurate their projections may be. Similarly, note the sceptics, scientists can’t say precisely what percentage of the current warming trend is attributable to human greenhouse gas emissions, as opposed to natural variability. For these and other reasons, the sceptics conclude, the alleged scientific consensus on human-caused global warming is shaky at best. Further, they argue – and this is crucial – the case for political action to reduce emissions is weak.

Sceptics vs science

Climate sceptics are also at odds with virtually all of the leading scientific authorities on global warming, including the U.S. National Academy of Sciences and the Intergovernmental Panel on Climate Change (IPCC). Further, as this article in Mother Jones points out, they are frequently allied with or directly supported by fossil-fuel interests and pro-industry think-tanks.

Still, let us acknowledge that while a scientific consensus on global warming indeed exists, that fact alone does not automatically confer upon the consensus view the status of eternal truth. After all, when the IPCC stated in 2001 that “most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations,” the word “likely” has a precise meaning: a 66-90% chance that the result was true. That also leaves some possibility that it might be untrue.

Uncertainties may be reduced with the appearance of the next IPCC report, slated for 2007. For the present, however, the sceptics persist, as do the uncertainties. And while it may seem more rational for the average politician or citizen without a scientific training to trust in the conclusions of the IPCC rather than in the contrary claims of a few doubters, some will always side with the supposed “underdog”.

But there is an inconsistency here that’s seldom remarked upon. Where are the global-warming sceptics who, despite their qualms about the science, support taking action now to curb the threat of global warming just in case it does turn out to be a major danger? Where are the sceptics who, despite their personal dissenting opinions, nevertheless acknowledge that as a general rule, politicians faced with tough decisions should rely on mainstream scientific opinion rather than far-out perspectives?

That such individuals are rare or non-existent tells us something. Not only do those in the global-warming sceptic camp have political commitments that overlay their scientific ones; they also have a muddled view of how science-based decisions should be made. For while we cannot entirely rule out the possibility that the current consensus on human-caused climate change is wrong, we can unequivocally rule out the notion that we should base present day political decisions on the remote hope that such a possibility might someday be realised.

Dissent, consent and uncertainty

So far as I know, Immanuel Kant has not yet been invoked during openDemocracy’s debate on the politics of climate change or, indeed, in most discussions of global warming. That’s a shame. Kant, you may recall, formulated the categorical imperative. This states that one should act only according to such a standard as you would wish people to universally adopt in their behaviour: “act only according to that maxim by which you can at the same time will that it should become a universal law.”

When it comes to science policy decision-making, global-warming sceptics demonstrably fail to do this. Or, if they do, then they must believe the following things: one, On every issue where scientific dissent exists, politicians should side with that dissent rather than the mainstream view; and two, on every issue where some scientific uncertainty exists, such uncertainty justifies political inaction.

But such positions are simply indefensible. Consider first the question of dissent. Scientific dissent pervades a wide range of issues; again and again, we see attacks on mainstream conclusions from special interests and their allied scientists. It happened with acid rain and depletion of the ozone layer, for instance. Yet when it comes to policymaking, are we seriously supposed to privilege dissent simply because it exists and ignore the mainstream scientific view?

Dissent has its place, certainly. But at the end of the day, those making policy decisions need to base them on a very particular kind of scientific information: collaborative, peer-reviewed scientific consensus documents or reports produced by bodies composed of a wide range of scientists with relevant expertise – also known as the IPCC reports. Such documents represent the best means available for non-scientists to access and understand the current state of scientific knowledge.

To repeat, that doesn’t mean such reports are infallible. But it does mean that, as a general rule, they provide the most suitable guidance for politicians – precisely why the world’s governments create such agencies in the first place. And of course, if subsequent scientific findings call political decisions into question, politicians (like scientists) must remain open to the possibility that they may have been wrong.

Scientific uncertainty is the norm in science policy debates, not an exception. There will always be unanswered questions. Policy-makers will always have to make choices despite incomplete information. Yet that makes it absurd to argue, as US climate negotiator and sceptic favourite Harlan Watson did recently, that immediate action isn’t warranted because the science of global warming remains uncertain.

Although some uncertainty persists, much is also known – and, as David King writes in the openDemocracy debate, that knowledge paints a fearsome picture of the possible consequences of delay in addressing the looming climate catastrophe. In the face of such knowledge, mere uncertainty cannot justify inaction because such inaction could itself compound the later consequences.

In sum, it is rational to allow for the remote possibility that global-warming sceptics may someday overturn the mainstream view. But that doesn’t mean we must delay political action while they attempt to do so.

Unfortunately, this distinction between the state of scientific debate and the demands of policy-making frequently gets lost. Whenever I write about global warming, for instance, I get bombarded with emails from sceptics who want to argue about the science. Their unspoken premise is always that there’s a “debate” or a “controversy” that must be settled before action can be taken. But that’s completely backwards. The truth is that action must be taken even though a debate at the fringes of the science may continue.