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Lessons of the James Hansen Affair
Eppur si muove — “and yet it moves” — was supposedly Galileo’s final statement after being forced by the Church to retract his revolutionary cosmological theories. He had run up against the overwhelming consensus of his time — that the Earth was the center of the universe and that saying otherwise was detrimental to the public good, not to mention Galileo’s health. For centuries, the scientific method has been an antidote to such persecution. Right or wrong, scientists should be free to advance their theories without the threat of extra-scientific censure, except perhaps when national security is at stake. Science alone should judge scientific validity.
Yet today, there appears to be a band of scientists and agitators who are willing to use the methods of Galileo’s persecutors to protect their own cherished theories. In the field of climate science, some people want to declare the scientific debate closed, allowing only those public statements that advance the approved idea that global warming is occurring, that man is responsible for it, and that it will probably be catastrophic unless greenhouse gas emissions are drastically curbed.
In its most extreme form, this phenomenon has involved calls for scientific versions of the Nuremberg Trials (from a writer at the environmental magazine Grist) and the equation of “climate change denial” with Holocaust denial. Others have branded as criminal those who question restrictions on greenhouse gas emissions. In September 2006, on CNBC’s Global Players program, Jeremy Leggett, CEO of a solar power company, called for fellow guest Fred Smith, president of the Competitive Enterprise Institute (the think tank where I work), to be locked up for expressing his views. James Hansen, head of NASA’s Goddard Institute for Space Studies, who has vociferously complained in the media of being silenced by the Bush administration for his research on global warming, suggested — without a hint of irony — that Mr. Smith should not even have been given such a platform for his views.
So just what is the nature of the “denial” that these scientists and environmentalists want to eradicate? First, there is the proposition that the Earth may not be warming at all. The truth is that there are not many scientists who publicly express this view nowadays. While there are many who question the reliability of surface temperature records, there are few who dispute the evidence from satellite records showing that the Earth has warmed 0.13 degrees Celsius per decade since the start of the data in the 1970s. These records, however, also show virtually no warming in the Southern Hemisphere (global warming isn’t very global). There is ongoing scientific debate about the calibration of the data, but essentially this debate is over: The Earth has warmed since the 1970s.
Yet that isn’t a very long time at all, certainly not long enough to establish whether or not the warming is so unprecedented that civilization and the biosphere have not had to deal with similar warming before. So the second target of the “denial” charge is those who dispute that the current warming is unprecedented. Yet here there is clearly ongoing scientific debate, with developments in just the past few months. A small group of paleoclimatologists issued a series of temperature reconstructions finding that global temperature was mostly stable for the past thousand years until a precipitous recent rise. Questions, however, were raised about the quality of the data and the statistical methods used to achieve this result. A team of eminent statisticians charged by the House Energy and Commerce Committee to investigate the scientists’ methodology confirmed that the methods they had used virtually guaranteed the result they obtained. Meanwhile, the National Research Council (NRC) found that the quality of the historic data meant that nothing more could be said with certainty than that the current warm period is warmer than at any time since the 1600s, which the NRC agreed was part of the “Little Ice Age” — something that the paleoclimatologists’ reconstruction suggested had not occurred. The NRC found that the suggestion that the current warm period was the warmest for a thousand years was merely plausible, but both unprovable and unfalsifiable given the current state of the historic data. The NRC also upheld the methodological criticisms. It is therefore somewhat of a stretch to claim that science has proven beyond reasonable doubt that the current warm period is unprecedented.
Third, the “denial” charge is aimed at those who purportedly suggest that mankind has nothing to do with the current warming. This represents a considerable oversimplification of the issue. Such “contrarian” scientists — such as S. Fred Singer, Patrick J. Michaels, and Richard S. Lindzen — have affirmed time and again that mankind is responsible for some of the warming. Basic physics indicates that the more greenhouse gases in the atmosphere, the more heat will be trapped there. Yet there are far more climate “forcings” than just greenhouse gases. The Intergovernmental Panel on Climate Change (IPCC) and the NRC both admit that our current understanding of these other forcings is low. Until we know much more about land-use change, aerosols, and solar activity, to name but a few, we cannot be certain that greenhouse gases have been driving the recent warming trend. That is why the NRC concluded that, “Because of the large and still uncertain level of natural variability inherent in the climate record and the uncertainties in the time histories of the various forcing agents (and particularly aerosols), a causal linkage between the buildup of greenhouse gases in the atmosphere and the observed climate changes during the twentieth century cannot be unequivocally established.”
The final charge against “deniers” is that they fail to acknowledge that global warming will be catastrophic. Most deniers would happily cop to this accusation, and they have plenty of evidence to back up their stance. When Al Gore talks about twenty feet of sea-level rise from the melting of the West Antarctic Ice Sheet (WAIS), he is failing to acknowledge the science. The IPCC estimates less than a meter of sea-level rise this century and considers catastrophic destabilization of ice sheets unlikely. Even if the WAIS were to melt, research indicates it would take several thousand years to do so, more than enough time for people to get out of the way.
The facts are similar with regard to most other supposed “catastrophic” impacts. Even if the theories linking increased sea surface temperature to more intense hurricanes are correct — and the hypothesis is the subject of intense ongoing debate — hurricanes will only be about 5 percent stronger by 2100 in a worst-case scenario. Polar bear biologists dispute whether or not the Arctic ursines are under any real threat from the melting of Arctic ice — 15 of 17 populations do not even appear to be affected. Some evidence from nineteenth-century Arctic explorers even suggests that ice sheet extents were as receded then as they are today. The same holds true for claims about air quality, heat waves, and precipitation. There is no uncontested, compelling scientific evidence that the effects of global warming will be catastrophic to health and welfare.
So if that’s all that the climate change denial charge can mean, why is it being made with such enthusiasm? The answer seems to be the chilling effect it has on the scientific debate. It makes public profession of opposing views unpalatable. Thus, Richard Lindzen of M.I.T. argues, “Scientists who dissent from the alarmism have seen their grant funds disappear, their work derided, and themselves libeled as industry stooges, scientific hacks, or worse. Consequently, lies about climate change gain credence even when they fly in the face of the science that supposedly is their basis.”
There is another, even more worrying result of the denial charge. It enables alarmists to portray the science as dispositive. The only way to solve the problem, science supposedly shows, is to reduce greenhouse gas emissions radically. Anyone who argues against this conclusion is deemed a denier.
Yet in public policy, science is not dispositive. Economic, political, and moral considerations also need to be taken into account. Practical tradeoffs and competing priorities need to be considered. By tarring those opposed to climate-change policy with the charge of denial, the alarmists have elided the economic, political, and moral debate to their great advantage.
Even worse, the denial charge obscures the many uncertainties that surround our understanding of climate change and its implications. Global warming is a serious enough subject that it needs to be debated fully, submitting every hypothesis to rigorous testing and hard-headed analysis. When the alarmists say the debate is over, responsible scientists and policymakers must reply, like Galileo, “And yet it moves.”