Monday, March 3, 2008

Dealing with Skeptics

The New York Times reported on Sunday that climate change skeptics are drawing attention to the recent cold weather in China and other places to cast doubt on climate change. (See I have not written on the science before, because I did not think it was necessary, but maybe this is an excuse to rehearse the argument I use on the increasingly rare occasions when I am faced with a skeptic.

Frequently I find there is a misunderstanding that scientists are somehow struggling to explain observed climate change. Nothing could be further than the truth. Climate change due to human activity -- anthropogenic climate change – was predicted by John Tyndall as early as 1860 (see and has been vigorously promoted by James Hansen of NASA (see for example since the 1970’s. In other words the theory preceded the observed effect.

Because of this, the focus over the past decade or so on whether we are actually observing climate change has been a diversion which has had the effect of wasting a lot of time during which we could have been taking action. Of course, the scientific method requires that we test our theories by observation, but there are different kinds of scientific theories. Testing climate change by observation is not a defining moment for science, like for example demonstrating that light gets bent by gravity validating the general theory of relativity. It is more like watching a heated kettle of water in the expectation that steam will appear from the spout. If it does not, we have some serious rethinking to do, but nobody seriously doubts that it will. Arguing about whether we actually can see the first wisp of steam is not very productive.

In the case of climate change, if it did not happen then we would have to rethink a good deal of the physics we thought we have known for over a century. It is a simple energy imbalance due to the absorption spectra of greenhouse gases and the different spectra of incoming radiation from the sun and the outgoing radiation from the earth. More heat comes in than goes out, so the earth warms up until it reaches a new equilibrium. Except that right now we are adding to the greenhouse gases to this equilibrium temperature keeps rising.

(It is perhaps worth noting here the amount of inertia in the system. Even if we could stop all greenhouse gas emissions today, stablizing the current concentration of these gases at 380 ppm of carbon dioxide equivalent, the average temperature of the earth would still continue to rise for decades. And then of course there is inertia at the next level down, in that we cannot stop the emissions today. The goal of IPCC efforts is to stabilize the concentration at 450 ppm.)

The precise effects of climate change in specific regions are much less certain, and skeptics often seize on this uncertainty. The reason for the uncertainty is that the heat landing on the earth is concentrated towards the equator, whereas the radiation from the earth is more evenly spread. Heat gets transferred from the equator towards the poles by air and sea currents, and predicting how these will be affected by climate change is much more difficult than the simple energy-balance model which tells us that the average temperature of the earth has to increase. Some places may get wetter, others drier, some may even get colder. There are very complex computer models but they probably cannot be relied upon as definitive. What we can be pretty sure of is that there will be disruptive changes.

If all the above fails to convince a skeptic, one can always fall back on the last resort sometimes known as the precautionary principle. If there is even a significant chance of catastrophic effects of anthropogenic climate change is true, does it not make sense to act as if it is true? If we were in a car heading towards what looks like a concrete wall we would not delay braking because it might be a paper mock-up, still less because we could not predict exactly which bones we would break.

As I write this, NPR is running a story about one example of a possible local effect. The locks on the Panama Canal are being widened and deepened to take larger ships. Its operation is however threatened by climate change because it depends upon rainfall. The canal rises 85 feet above sea level and the water for the locks on both sides is gravity-fed fresh water from artificial lakes. Climate change could reduce rainfall and threaten its operation. Of course, by then the Northwest Passage may be a viable alternative.

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