The Sciences

Freeman Thinking

Cosmic VarianceBy John ConwayMar 30, 2009 12:48 AM


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Today's New York Times magazine had a long feature on Freeman Dyson, loosely based on his skepticism about global warming. Dyson, one of the founders of modern relativistic quantum field theory, is skeptical about a lot of things, as a matter of fact. Freeman spent two weeks at our department at UC Davis last year, gave a public lecture, a colloquium, and was available for a number of very stimulating conversations. We had lunch with him one day, and pressed him on his taste for smaller, lighter, faster experiments in particle physics, as opposed to the dominant large collider experiments such as those at the LHC, the Tevatron, and LEP. In his kind way, Freeman said it was all fine with him that such things took place, but that he simply preferred the more table-top variety, where the individual experimenter could control the variables and the measurement at hand. I do too, but as the NYT article quoted Weinberg as saying, "get over it!" Anyway, about global warming. I have to say that my own skeptical streak doesn't simply cave to the present dominant stream of thought on this issue either. As scientists we need to continue to question all of it. It seems to me that the dominant paradigm can be summarized in a number of straightforward notions:

  • The earth's climate is in an overall warming trend. The average global surface temperature, and the average surface temperature of the oceans, is increasing.

  • The root cause of the increase in global surface temperature is in large part, or even dominantly, due to the increase of the level of greenhouse gases such as CO2 and methane in the atmosphere.

  • The dominant source of the excess greenhouse gases is human activity: industry, transportation, agriculture and the like.

  • If the global surface temperature continues to increase, then drastic and devastating consequences will ensue due to the melting of polar ice and the rising of sea levels, desertification of huge swaths of land, increased frequency and intensity of devastating storms, and other effects.

  • By changing our means of energy production and ceasing the use of fossil carbon fuels as soon as possible, there is still a chance that we can evade the above ill effects.

My own skepticism increases linearly as we go down this list. The first two items, that the global surface temperature is increasing, and that it is due to greenhouse gases, seems to be incontrovertible. The extensive measurements and correlations reported by the IPCC are rather hard to refute at this stage. (It is a very great setback for this science that NASA's Orbiting Carbon Observatory crashed on launch last month, or we would have gotten the mother lode of data on these questions.) That the dominant source of excess greenhouse gases seems incontrovertible as well, though here the climate models start to differ about the sources and sinks of global CO2, methane, and other gases. And, as the climate changes, not all the models can possibly predict all the outcomes. An example: in 2005, the Amazon experienced a drought which turned the region, with over half the world's rainforest, from a net carbon sink to a net carbon source. Was the drought predicted by any (or all) of the models? Was the net effect on carbon predicted? The best models must combine physics, oceanography, chemistry, and biology all at once. Has it really been done yet? (Enlighten us all, gentle readers, if you know!) Then the last two: the negative effects. We dwell on these. Clearly ocean levels will rise rapidly in our lifetime if Greenland melts, and it appears to be melting faster than expected by the models. That would be a bad thing, especially here in the Central Valley of California. My house is 15 meters above sea level, and a lot of the roads around here are lower than that. If Greenland melts, sea level will rise over 7 meters. Well, the Central Valley used to be a sea, and it will be again some day, no doubt. And with so much of the world's population living so close to the sea, this is a serious, serious concern. I am less convinced about the severity and frequency of storms with global warming, but my mind is open to being convinced by good science. Lastly, can we do anything about it? The whole question of whether we've reached a "tipping point" seems to be hot right now. The answer lies in the climate models, so let's keep our skepticism alive here. We don't understand what causes ice age cold and warm spells. When those are in the models, and we can post-dict the previous glaciations, I'll start to believe the models. The oceanic thermohaline circulation seems to be key here, but how? What about the Milankovich cycle? Chaotic perturbations in the solar system? Dust lanes in the Milky Way? No one said this would be easy... And how soon could we wean ourselves from carbon, even if we wanted to? Oil may run out, but there is a crapload of natural gas and coal left to burn. Remember, "drill, baby, drill!" is the same as "burn, baby, burn!" And we have a lot left to burn. I am not convinced at all that in 10 years we can "Repower America" and eliminate fossil fuels. And the rest of the world certainly won't. That doesn't mean we should not try, should not do research into new, non-carbon-based energy sources, expand our use of renewable, clean energy. We should! I am just very skeptical that it could be done even if it became the #1 national priority. It seems to me to violate physics itself, not to mention basic economic facts. Twenty years? Thirty? Eventually it will be clear to every one that we don't really have a choice. Sigh...Freeman, what's the answer?

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