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Why Weather Forecasts Are Full of Hot Air

By Jocelyn SelimJanuary 1, 2002 6:00 AM


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Long-term weather and climate forecasts are notoriously unreliable. Kevin Trenberth and Julie Caron at the National Center for Atmospheric Research have just made the job more predictable by nailing down a big unsettled question: How much of Earth's heat travels through the atmosphere, and how much through the oceans? Climate researchers have long had to rely on crude estimates of heat flow over the oceans based on measurements gathered from balloons and airplanes. The amount of heat transported by ocean waters was calculated by subtracting the atmospheric component from the total heat transport determined by satellites. But when the first actual ocean heat measurements started arriving a few years ago, the numbers simply didn't add up.

After reanalyzing the results with data from new satellites, Trenberth and Caron now know why: The air is moving a lot more heat than early studies had indicated. "On a global level, the atmosphere is the much larger player," says Trenberth. At 35 degrees latitude, the atmosphere carries 78 percent of the total heat flow in the northern hemisphere and 92 percent in the southern hemisphere. "When you compare this model to real-world measurements of ocean and air temperatures, they all finally match up," he says. "Now we can start talking more intelligently about global warming."


A temperature map provides a weather snapshot—but what's behind the picture?Courtesy of Space Science and Engineering Center


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