The data arrive from a multiplicity of sources. Twice a day, weather balloons are released around the globe to measure nitrous oxide, methane, and carbon dioxide residing in the atmosphere. Drifting ocean sensors record sea temperatures and beam home the data via satellite. Scientists work daily to manipulate complex computer simulations to model the sea surface temperatures 200 years ago to make comparisons to the temperatures today. Satellite remote sensing and laser technology are used to measure the amounts of sunlight absorbed and reflected by ice sheets, while others attempt to see how changing rainfall patterns and rising temperatures affect foliage and the land's ability to absorb carbon. New mathematical models also are being developed to more accurately predict patterns of cloud formation, as clouds reflect sunlight and absorb and trap various amounts of energy, depending on shape and height. For instance, lofty, narrow cloud columns associated with heavy storms will tend to block less of the sun's radiation than wide blankets of shallow clouds. Fung says that clouds are a "very sensitive dial in the climate system."

Understanding historical weather patterns also helps experts predict the future, so scientists also have begun to scrutinize core samples collected from deep within Antarctic ice sheets, the so-called Vostok ice core, to discern more accurately what the planetary atmosphere used to resemble. By analyzing gas bubbles trapped within these glacial samples, experts can determine the amounts of dust, carbon dioxide, methane, and other gases that were in the earth's atmosphere hundreds of thousands of years ago. These core samples tell us, for instance, that CO₂ levels never exceeded 280 parts per million before the industrial age (about 200 years ago), while today the level is nearer to 380. To add to this growing basket of more accurate data, NASA in 2008 will launch the Orbiting Carbon Observatory, a new satellite that will measure the CO2 in the earth's atmosphere, an experiment that Fung is helping to fine-tune.

It does not ease Dr. Fung's mind that even as we speak, the Mid-Atlantic states are being drowned by record-setting floods that threatened Trenton, New Jersey and Wilkes-Barre, Pennsylvania; that a powerful storm in Australia is causing huge waves to pummel San Francisco's Ocean Beach; that wildfires are already breaking out across Arizona and California; or that it is way too early in the year for Texas to be facing another damaging drought.

Yet all these signals, she suggests, demonstrate that the fragile balance that keeps the earth's ecosystem functioning properly-a complex and finely regulated series of homeostatic effects that tends to maintain its stability for generations at a time-may, like some Hollywood sci-fi film, now be spiraling out of control.

"For years we have been building models to predict the weather," says Fung, who has been developing such complex simulations since she wrote her thesis as an MIT graduate student on the calculus of hurricanes and then eventually became a climate forecaster for NASA. "But now our weather is getting more and more extreme and this is consistent with what our theoretical predictions said. So whether it's the melting glaciers in the Arctic or the drying of grasslands or the rising temperatures ... these new observations tell us we've been correct -- that it's no longer merely a theoretical prediction."

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