Scientist builds case for global warming

Gabriele Hegerl left Paris a victor eight days ago -- one of an elite band of scientists who convinced 113 world governments that global warming is a man-made and urgent threat.

But back in Durham, the Duke University climate researcher is not strutting. For one, Hegerl is not that way. And although success with the Intergovernmental Panel on Climate Change is important, it's just one step.

"We can't go easily back. It takes a long time for greenhouse gases to build up and very long to remove them," says Hegerl, who at 45 could still be mistaken for a graduate student in wine-colored corduroys and a comfortable wool sweater.

The researcher most people know as Gabi didn't always strive for a leading role in this hot scientific field. The daughter of a tax official and foreign-language translator, she trained initially as a mathematician in her native Germany. Formulas depicting the physics of fluid dynamics drove her doctoral thesis.

In fact, climate change found Hegerl before she looked for it. She and friends observed troubling changes while climbing in the Alps. Glaciers kept turning up higher on peaks than where the maps showed them. Rising temperatures, they finally realized, were shrinking the ice.

When investigating where to pursue postdoctoral studies in the 1990s, Hegerl was impressed by the prestigious Max Planck Institute for Meteorology in Hamburg, where climate change already transfixed many researchers. There she learned to build complex computer models.

Models are powerful tools in science. They use measurements, statistics, mathematics and computer power to mimic natural systems such as Earth's climate, which is too huge to observe as a whole.

These days researchers use such models to predict how the burning of fossil fuels, a practice that has steadily expanded since the early 20th century, is changing the Earth. Emissions from car tailpipes and power plants contain carbon dioxide, a gas that acts like greenhouse glass and traps heat on the planet's surface.

Rising sea levels, stronger hurricanes and melting polar ice are among the predicted outcomes from global warming. The conclusions produced by models, of course, are only as good as the data used to build them.

The Planck Institute sent Hegerl to the United States for further training. But instead of going to the Scripps Institute of Oceanography -- a plum assignment partly due to its location in La Jolla, Calif. -- Hegerl was dispatched to Texas A&M University in central Texas in the mid-1990s. At first, she balked.

"I told them I don't want to see a cowboy; I want to see the ocean," Hegerl recalls.

But it was a lucky move. In College Station, Hegerl met her husband, Thomas Crowley, a climate researcher who hunts for evidence of weather conditions in the past, sometimes more than a million years ago.

Even after marrying, Hegerl and Crowley lived apart at times while she continued training. In 2001, both accepted jobs at Duke.

At the leading edge

Over the years, the unpretentious woman with a ready smile has developed into a precise, clever and observant scientist with international standing in her field, says Francis W. Zwiers, director of the climate research division for the Canadian Department of the Environment.

"Worldwide, half a dozen people are working at the leading edge of this. Gabi is one of those people," Zwiers said. He and Hegerl led a three-year effort to assemble reliable science used to craft a portion of the Paris consensus statement -- the strongest international statement on global warming yet.