60-Second Earth

Michael Mann Defends Climate Computer Models

Penn State climate modeler Michael Mann talks about what computer models can tell us--and what they don't need to. David Biello reports

Fair warning: the following is more than 60 seconds, and it’s about climate change.

"Even in high school my idea of a good time was sitting in front of a computer and solving problems." Climatologist Michael Mann. “And that has always been true. I love using computational methods to learn about the way, hopefully, the way the world actually works.”

Some critics, such as physicist Freeman Dyson, charge that climate change science relies too much on such computer models. And even worse, that the climate scientists behind them are too much in love with their computational creations. Such mathematical approximations are crude, failing to capture the real world climate impacts of a cloud, for example. That makes them useful for understanding climate but not for predicting climate change, Dyson has argued. I asked Mann in a recent phone interview how he responded to such arguments.

"I have to wonder if Freeman Dyson will get on an airplane or if he’ll drive a car because a lot of the modern day conveniences of life and a lot of our technological innovations of modern life are based on phenomena so complicated that we need to be able to construct models of them before we deploy that technology.

“In the case of the climate, of course, there is only one Earth, so we can’t do experiments with multiple Earths and formulate the science of climate change as if it’s an entirely observationally based, controlled experiment. We need to rely on conceptual models of the system we’re studying and it’s no different in any other field of science. In fact, the way science progresses is by conceptual models being put forward and then testing them against observations. One of the most, I think, striking examples of that was just within the last month, this announcement, the Higgs Boson.

“Its existence was predicted by the standard model of particle physics and the fact that there’s—we got a glimpse of it, it looks like it may very well be there—is a real victory for that model of science where you test, you put forward conceptual models of the way the world or the universe works and test those models against the observations and see the extent to which they can predict new observations and when they do, it gives you increased confidence in the models.

“It’s no different in the case of climate change.  The models are simply at some level a formulation of our conceptual understanding and when someone says they don't like models then I’m wondering what alternative they have in mind.

“How do they formalize their conceptual understanding? Through back-of-the-envelope, poorly conceived thought experiments?  It's somewhat bewildering when I hear something like that from a premier scientist, and I think it belies a misunderstanding of the way models are used. In climate science, for example, where we don't need an elaborate climate model to understand the basic physics and chemistry of greenhouse gases, so at some level the fact that increased CO2 warms the planet is a consequence of very basic physics and chemistry.

“The details, how much warming you get, depend on things like feedbacks. And you can’t incorporate feedbacks through a back of the envelope approach.  You actually have to critically think about the interactions that take place in this very complex system. And those feedbacks ultimately determine the extent to which that initial warming will be amplified, but they don’t even change the fact that you elevate greenhouse gas concentrations in the atmosphere and you’ll get a warming of the surface. That’s basic physics and chemistry and people who claim that they don’t believe that, they don’t believe we’re warming the planet through increasing CO2 levels because of climate models, they don’t understand the fact that you don’t need a climate model to come to that conclusion. It's basic physics and chemistry.

“The climate models come in because we wanna know how that's modified by feedback.  What are the important feedbacks?  How will atmospheric circulation patterns change? And again, does Freeman Dyson, assuming he is willing to get on an airplane even though models have been used to test the performance of the airplane, assuming he does and he knows he’s going somewhere where they’ve predicted, where weather models have predicted rainfall for the next seven days, does he not pack his umbrella because he doesn’t believe the models? It's just in that case the worst that will happen is somebody gets wet when they wouldn’t otherwise have. In this case, the worst that can happen is that we ruin the planet.”

—David Biello

[The above text is a transcript of this podcast.]

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