Scientists' use of computer models to predict climate change is under attack

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By David A. Fahrenthold
Washington Post Staff Writer
Tuesday, April 6, 2010

The Washington Nationals will win 74 games this year. The Democrats will lose five Senate seats in November. The high Tuesday will be 86 degrees, but it will feel like 84.

And, depending on how much greenhouse gas emissions increase, the world's average temperature will rise between 2 and 11.5 degrees by 2100.

The computer models used to predict climate change are far more sophisticated than the ones that forecast the weather, elections or sporting results. They are multilayered programs in which scientists try to replicate the physics behind things such as rainfall, ocean currents and the melting of sea ice. Then, they try to estimate how emissions from smokestacks and auto tailpipes might alter those patterns in the future, as the effects of warmer temperatures echo through these complex and interrelated systems.

To check these programs' accuracy, scientists plug in data from previous years to see if the model's predictions match what really happened.

But these models still have the same caveat as other computer-generated futures. They are man-made, so their results are shaped by human judgment.

This year, critics have harped on that fact, attacking models of climate change that have been used to illustrate what will happen if the United States and other countries do nothing to limit greenhouse gas emissions. Climate scientists have responded that their models are imperfect, but still provide invaluable glimpses of change to come.

They have found themselves trying to persuade the public -- now surrounded by computerized predictions of the future -- to believe in these.

If policymakers don't heed the models, "you're throwing away information. And if you throw away information, then you know less about the future than we actually do," said Gavin Schmidt, a climate scientist at NASA's Goddard Institute for Space Studies.

"You can say, 'You know what, I don't trust the climate models, so I'm going to walk into the middle of the road with a blindfold on,' " Schmidt said. "But you know what, that's not smart."

Climate scientists admit that some models overestimated how much the Earth would warm in the past decade. But they say this might just be natural variation in weather, not a disproof of their methods.

As computers have become faster and cheaper, models both simple and sophisticated have proliferated across government, business and sports, appearing to offer precise answers to questions that used to be rhetorical.

How many games will the Redskins win next season?


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