Sherwood replies: The letters here in response to my article raise legitimate points but also propagate some common confusions.

Most important, Robert Adair, William Dickinson, and Ron Larson blur the distinction between the basic physical principles of global warming and the provision of dire forecasts or calls for action. My article was very specifically about the acceptance of the underlying physics of global temperature, not claims about specific consequences, which are arguably unpredictable, or about policy, which is a matter of judgment. As scientists we must hold this distinction and help others to do so, because the essence of clear thinking on any difficult issue is to break it down into smaller pieces. It is one thing to claim that anthropogenic climate change is not worth addressing, but quite another to deny its reality or basis in physics. People’s assessment of the evidence tends to be driven by their policy views rather than the reverse.1 This inversion of reason may not be new, but it is certainly not good for science.

The description Adair cites by Irving Langmuir and Robert Hall of the harebrained ideas championed by some self-deluded physicists is indeed appropriate—but the true parallel is with the ideas floated by climate contrarians. Compare, for example, the enchanting early-1900s story of “N rays” with the current idea that the Sun has caused warming, perhaps by modulating cosmic-ray fluxes: True solar believers ignore the absence of any recent trend in observed solar activity, rely on data correlations that fail proper significance tests, and invoke mysterious amplification factors to enable tiny changes in solar irradiance to compete with the far larger and directly measurable power input by added greenhouse gases. They do not explain where the greenhouse gas power input is going if it is not heating the planet, and they must dismiss as coincidence its accord with the rate of accumulation of enthalpy in the world’s oceans. That may exceed the worst of Langmuir and Hall’s examples of hope over common sense.

Moreover, Adair is wrong in asserting that such flubs met with “similar receptions” to ideas now heralded. The way to find common sense is to look for assessments that are common among those who should know. Langmuir and Hall point out that the harebrained ideas were never accepted by a clear majority of experts and eventually by only a handful who could not let go. That is also the trajectory of contrarian theories of climate. Unfortunately, there are always rewards for telling people what they want to hear, so the handful of expert contrarians will not disappear anytime soon and may even grow for a while. A couple of them may be highly respected, but respect has never conferred immunity to self-delusion or opportunism.

As for successful predictions quite reasonably requested by Sergio Rojas, the warming forecast in 1990 in the first report2 by the Intergovernmental Panel on Climate Change remains on target both in terms of global mean and approximate geographical patterns; we have also seen stratospheric cooling and a host of other long-predicted side effects. Given the stochastic behavior of the system, one cannot ask for much more without waiting several more decades for the warming signal to grow bigger. Albert Einstein’s prediction of light bending may have been a lot more precise, but neither prediction put skepticism to rest at the time, no matter how conclusive it may look in hindsight.

I agree with Adair that if no warming were to occur over a 20-year period, experts would have some explaining to do, but currently there is no sign of that happening. He questions the statistical significance of warming since 1998, but that is a red herring; trends over a mere decade are seldom significant no matter what climate is doing. One must look over longer periods.

To Nicholas Van Buer I say that I meant no slight against geologists—or geoscientists, a category he mentions that also includes geophysicists. I spent many years working alongside geologists and am greatly impressed by how they approach and solve such complex puzzles. But those problems do tend to engender in geology a different approach from that favored in physics, where the systems studied are simpler. Each approach has its advantages and its blind spots. In a way I was defending the physics approach, which I suspect is the less intuitive for most people and easy to belittle if not understood.

J. T.
G. J.
J. J.
, eds.,
Climate Change: The IPCC Scientific Assessment
Cambridge U. Press