Eminent physicist Freeman Dyson raised eyebrows a month ago when he told the New York Times Magazine that a little extra carbon dioxide—and global warming—might turn out to be good for the planet. So when we saw his name on an event around the corner from Scientific American's offices we figured we'd go hear his criticisms, dubbed "Climate Disasters, Safe Nukes and Other Myths," firsthand.

At the luncheon put on by the Cato Institute, when the talk turned to climate change Dyson started out sounding as if the whole thing was overblown, noting that the prospect of global warming is a problem that should be taken seriously. But he also said that no one should be alarmed about it yet.

Then he outlined his main criticism: Too much of the science of climate change relies on computer models, he argued, and those models are crude mathematical approximations of the real world. After all, a simple cloud—small in scale, big in climate effects, the product of evaporation and condensation, all of which it is difficult to create equations for—eludes the most sophisticated climate models.

So climate modelers turn to what they call parameters or, as Dyson likes to call them: "fudge factors." These are approximations, such as the average cloudiness of a particular spot at a particular time, that are then applied globally. With the help of about 100 of these parameters, models can now closely match the world's present day climate, Dyson says. These models then, like the one developed at Princeton University where Dyson is a professor emeritus, are "useful for understanding climate but not for predicting climate."

That's too much of a temptation for scientists working on the problem, however. "If you live with models for 10 to 20 years, you start to believe in them," Dyson said, witness the implosion of the financial markets after over-reliance on quantitative models. He characterized this over-reliance as a disease infecting everything from physics to biology: "A model is such a fascinating toy that you fall in love with your creation."

Ultimately, "every model has to be compared to the real world and, if you can't do that, then don't believe the model." And he noted that the real world has been through some significant climate changes before: witness a lush Sahara Desert thousands of years ago or the forests that once covered Greenland.

Of course, models have been tested against the real world (both today's and eons ago's) and many of Dyson's other objections have been rebutted elsewhere. He also did not address the real world impacts already observed: ice melt, sea level rise, ocean acidification and more. His main concern seems to be that worrying about climate change distracts from more important problems such as poverty and infectious disease. Many might note that poverty (the inundation of Bangladesh) and infectious disease (improved conditions for transmission) are also problems exacerbated by climate change.

But Dyson's purpose seems to be to throw out "heretical" ideas that can then spur further debate. (As even he would admit, his heresies are a little more grounded in the real world when he's talking about nuclear weapons. Before discussing climate change, he told a roomful of people who probably want to put former President Ronald Reagan on Mount Rushmore that the Great Communicator blew a real chance to rid the world of nuclear weapons in 1986 because he was too attached to the "Star Wars" missile defense program.) As he said: "I know a lot about nuclear weapons and nothing about climate change."

"I like to express heretical opinions," Dyson said, with an impish gleam in his eye. "They might even happen to be true."

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