Word: modelling
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Dates: during 1980-1989
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Take the Antarctic ozone hole, for example. Before it was discovered, climate modelers trying to simulate ozone loss in the atmosphere had not yet factored in the presence of ice clouds in the Antarctic stratosphere. Thus their models failed to predict the existence of the ozone hole. After the hole was finally stumbled upon two years ago, Susan Solomon, a chemist at the National Oceanic and Atmospheric Administration in Boulder, and Rolando Garcia, of the National Center for Atmospheric Research, plugged more numbers into NCAR's computer model to account for the Antarctic ice clouds. Bang! The hole appeared...
Does that mean, as one critic put it, that models projecting climatic change are "just the opinion of their authors about how the world works"? Not necessarily. That the model eventually proved accurate, if only in hindsight, was a tribute to the powers of computer climate models -- and a demonstration of their shortcomings. The models attempt to reduce the earth's climate to a set of grids and numbers, then manipulate the numbers based on the physical laws of motion and thermodynamics. The sheer number of calculations involved is mind-boggling. A three-dimensional model, for example, requires more than...
Even so, climate modelers admit, building a completely realistic mock earth is an impossibly tall order. "You divide the world into a bunch of little boxes," explains Michael MacCracken, an atmospheric scientist at Lawrence Livermore National Laboratory. The size of the geographic box -- the degree of detail called for -- limits the model. Smaller grids dramatically increase the number-crunching power required. "The state of the art would be to get down to small areas so we can say what's going to happen in Omaha," says Livermore's Stanley Grotch. "The models just aren't that good...
...major drawback of computer models is that the various data do not necessarily behave as a system. Coaxing ocean currents to interact with the atmosphere is no small matter. For starters, oceans heat and cool far more slowly than the atmosphere. "We've had a hard time coupling the two systems," admits Manabe. "Even though the atmospheric model and ocean model work individually, when you put them together, you get crazy things happening. It's taken us 20 years to get them together, and we're still struggling...
...Offsetting the obvious weaknesses of climate models, says Warren Washington, who developed the model now used at NCAR, is one significant advantage. "They are experimental tools that allow us to test our hypotheses," he says. "We can ask such questions as 'What happens when a big volcano like El Chichon goes off?' and 'How much will the earth warm up by 2030 if we continue to dump CO2 into the atmosphere...