Tuesday, January 18, 2011

Can we trust climate models? Increasingly, yes

A few snips from a long, worthy piece by Michael D. Lemonick In Yale Environment 360 does a fine job of explaining climate modeling: …[E]ven when you factor out the vagaries of politics and economics, and assume future emissions are known perfectly, the projections from climate models still cover a range of temperatures, sea levels, and other manifestations of climate change. And while there’s just one climate, there’s more than one way to simulate it… How much can we really trust climate models to tell us about the future?

The answer, says Keith Dixon, a modeler at GFDL, is that it all depends on questions you’re asking. “If you want to know ‘is climate change something that should be on my radar screen?’” he says, “then you end up with some very solid results. The climate is warming, and we can say why. Looking to the 21st century, all reasonable projections of what humans will be doing suggest that not only will the climate continue to warm, you have a good chance of it accelerating. Those are global-scale issues, and they’re very solid.”

The reason they’re solid is that, right from the emergence of the first crude versions back in the 1960s, models have been at their heart a series of equations that describe airflow, radiation and energy balance as the Sun The problem is that warming causes changes that act to accelerate or slow the warming. warms the Earth and the Earth sends some of that warmth back out into space. “It literally comes down to mathematics,” says Peter Gleckler, a research scientist with the Program for Climate Model Diagnosis and Intercomparison at Livermore National Laboratory, and the basic equations are identical from one model to another. “Global climate models,” he says, echoing Dixon, “are designed to deal with large-scale flow of the atmosphere, and they do very well with that.”

…And the models are constantly being improved. Climate scientists are already using modified versions to try and predict the actual timing of El Ninos and La Niñas over the next few years. They’re just beginning to wrestle with periods of 10, 20 and even 30 years in the future, the so-called decadal time span where both changing boundary conditions and natural variations within the boundaries have an influence on climate. “We’ve had a modest amount of skill with El Niños,” says Hurrell, “where 15-20 years ago we weren’t so skillful. That’s where we are with decadal predictions right now. It’s going to improve significantly.”

After two decades of evaluating climate models, Gleckler doesn’t want to downplay the shortcomings that remain in existing models. “But we have better observations as of late,” he says, “more people starting to focus on these things, and better funding. I think we have better prospects for making some real progress from now on.”

A shelf cloud from a thunderstorm supercell, from NOAA

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