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Why has it become taboo simply to point out that scientists disagree quite a lot about global warming?

With the Obama administration badly weakened by a string of political failures – most prominently its inability to stand up to Republicans on the issue of raising the government debt ceiling – attention has shifted to the Republican presidential primary candidates. In the past few weeks, Rick Perry, the governor of Texas, has catapulted to the lead position in the race.

Perry is known for his straight talk as well as for his discounting of the anthropogenic global warming theory. His stance on this issue has helped him gain attention and to burnish his credentials with conservatives. Speaking in New Hampshire recently, Perry opined that ‘there are a substantial number of scientists who have manipulated data so that they will have dollars rolling into their projects. And I think we are seeing almost weekly, or even daily, scientists coming forward and questioning the original idea that man-made global warming is what is causing the climate to change.’

Predictably, Perry’s provocative words attracted much scrutiny from political analysts. But among the rash of commentaries, there was a surprising and troubling convergence of opinion regarding the Texas governor’s views on global warming. One does not expect a whole lot of agreement between left-of-centre Paul Krugman and the rather more conservative David Brooks, both columnists for the New York Times. But here they were both using Perry’s position on climate change as a litmus test for his competence to be president.

Brooks referred to Perry’s appeal to the ‘alternative-reality right – those who don’t believe in global warming, evolution or that Obama was born in the US’. Krugman called Perry’s position ‘vile’ and retorted that the ‘scientific consensus about man-made global warming – which includes 97 per cent to 98 per cent of researchers in the field – is getting stronger, not weaker, as the evidence for climate change just keeps mounting’.

It is not a good sign when commentators as literate and intelligent as these two figures resort to a simplistic and pat reading of the science regarding climate change and use the issue as a litmus test for judging a political candidate. The role of intellectuals should be to penetrate beneath the self-indulgent glosses that promote alarm and confusion, and the New York Times columnists failed on this score.

Both Brooks and Krugman invoked the widely cited consensus on global warming that allows no rational dissent. In fact, the evidence supporting some effect of carbon-dioxide levels on global temperature is very strong. However, the magnitude of the effect is fairly small, and this is where the confusion lies. A quick calculation based on figures from the 2007 International Panel on Climate Change (IPCC) report shows that over the past 200 years the average increase in global temperature attributable to greenhouse gases is about one-quarter of a degree Celsius (1). This accounts for roughly one third of the 0.8 degrees Celsius observed warming over that period. (For reference, warming of one-quarter of a degree Celsius corresponds to moving 20 miles south in the Midwest of the USA.) Indeed, it is likely that 97 per cent of scientists do agree that this small amount of warming is occurring.

Beyond the agreement on this point, there is a wide range of opinions among scientists about climate projections over the coming century. This diversity of opinion is understandable in view of the fact that computer models used to describe future climate trends are sorely challenged by the complexities of the climate system – including the roles of cloud cover, water vapour (an important greenhouse gas), ocean currents and other factors – and feedback between different components of the system.

Another crucial point is that, short of a major shift to nuclear power – an option that has received a major setback due to the Fukushima triple meltdown – there is little that can be done to decrease man-made carbon dioxide emissions in the short to medium term without incurring enormous expense or greatly decreasing economic activity.

For the past five years, US public discussion of climate change has been dominated by two diametrically opposed extreme positions. These are personified by former vice president Al Gore, who painted the most extreme and alarmist scenario in his Oscar-winning documentary An Inconvenient Truth, and the Republican Senator from Oklahoma, James Inhofe, who maintains that global warming is a ‘hoax’.

What these positions have in common is a willingness to simplify what is a dauntingly complex phenomenon and to embrace an emotionally satisfying position, while failing even to acknowledge the immense uncertainties in the science regarding climate change. Once one embraces such a position, one has little trouble in finding evidence to support it.

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