The global warming debate

In the global warming (aka climate change) debate, I have been skeptical of both sides: those who say that the sky is falling and also those who say that the whole thing is a fraud. In my own conversations with climate scientists, I have found that they are much more careful and measured than the politicians and activists.

It is clear that carbon-dioxide levels are increasing and it seems likely that humanity is the principal cause. If we project future carbon-dioxide levels (an educated guess), it’s a simple physics calculation to determine the direct effect on the climate. The direct effect is not very large. But then there are the indirect effects. For example, slightly higher temperatures lead to polar ice melting, which leads to more water vapor, which either accelerates or counteracts climate change depending on the altitude at which the new clouds form. Predicting the future path of climate change depends entirely on the indirect effects, and we simply don’t know what they will be.

To try to guess the indirect effects, climate scientists have turned to computer models. Many of the models show dire consequences on increasing CO2 levels and some do not. Which, if any, of the models is accurate we simply do not know. The models generally do not make predictions that we can test, and those few that do have not performed well.

So when professional alarmists like Al Gore say the science of climate change is complete, they have it almost completely backwards. If we’re talking about projecting the future (which is what matters to public policy, after all), it would be more accurate to say that the science has not yet begun.

I am not a climate scientist, but I am a scientist. Science happens when you pose a hypothesis and devise an experiment that can test the hypothesis. (Or, better yet, when you prove a theorem, but that’s not in the cards for climate science.) In the physical sciences you can never prove a hypothesis conclusively, but if enough experiments fail to disprove it, you start to consider it confirmed.

When it comes to climate projection, all the models tell us is what will happen if the world responds in a particular manner. They have not been tested against the real world, and they can’t be. This isn’t the fault of the climate scientists; they’re doing the best they can. You simply cannot test long-term predictions in the short term. One does not have to be a climate scientist to recognize this fact.

Now it might be that the potential consequences of global warming are so dire that we must undertake a program of remediation without knowing what will happen. But it is plainly dishonest to claim that the science is done when it is not. Moreover, when it comes to policy, we must also recognize that there is another side of the equation, the economic question of what is possible. And there is considerable evidence that proposed strategies to fight global warming simply cannot be accomplished with existing technology.

My personal opinion is that we should look at reasonable, cost-effective steps for controlling CO2 emissions, such as expanding nuclear energy and researching new technologies such as carbon sequestration. We should also look seriously at geoengineering in case the worst comes to pass.

POSTSCRIPT: This post was occasioned by the scandal arising from the leaked emails and documents from the Hadley CRU. I’ll be writing about that shortly. (UPDATE: Here.)

UPDATE: Richard Lindzen, an well-respected and impeccably credentialled climate scientist at MIT, has an op-ed about climate feedback (what I called indirect effects) here. (Via Volokh.)

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