An Historian of Global Climate Change

Introducing the Newest Nicholas Chair

By Monte Basgall
Reprinted from Duke Dialogue

Thomas Crowley, Duke's new Nicholas Professor of Earth Systems Science, started out wanting to be a historian, but was throughly co-opted by the geological sciences. In a flashback to his roots, he is currently engaged in computer-assisted studies of Earth's climatic history, with an emphasis on current global warming.

"One of the things I like about climatic research is that you learn a lot about many different things," Crowley said in an interview in his new office in the Old Chemistry Building, where he was recently (fall 2001) unpacking equipment brought from Texas A&M University.

"You learn about the atmosphere and about the ocean. If you get into paleoclimatology (the study of ancient climates) you have to know about fossils. If you're interested you can also learn about evolution. You will learn about sedimentary rocks, and movement of continents and also about geochemical cycles."

He decided to come to Duke's Nicholas School because "the opportunities for growth in this area were very attractive. The provost has indicated an interest in supporting global change research, and that's something I'm very committed to."

Another attractant was Duke's reputation and encouragement for interdisciplinary research and for related policy studies. "When you're interested in global warming, that's inevitably interdisciplinary," he noted.

Last year Crowley published two articles in the world's top research journals that reprise his recent research efforts. The first was the cover story in the May 25, 2000 issue of Nature about "Simulating Snowball Earth." The second, in the July 14, 2000 issue of Science, assessed the "Causes of Climate Change Over the Past 1,000 Years."

Snowball Earth refers to a striking theory that the Earth of 600 to 800 million years ago may have been covered with ice all the way to the equator because of a particular arrangement of continental land masses.

While he didn't originate the hypothesis, which was based on geological evidence, Crowley and his longtime colleague, William Hyde, now a research associate at the Nicholas School and the first author of the Nature report, were able to come up with well-working computer models "that could simulate an ice sheet at the equator," he said.

He was gratified to find that some of his models allowed for "patches of open water" that would give the multicellular life in that era some place to survive.

The original hypothesis had suggested the ice might have frozen out all those multicellular forms, forcing life to restart from scratch. "I found that very hard to accept," he recalled. "I originally started out as a paleontologist interested in fossils. It took 3 billion years to evolve multicell animals."

The Science article, which Crowley authored alone, used computer simulations to look for causes that could produce the "Medieval Warm Period," the "Little Ice Age" that followed, and the striking and accelerating warming trend that characterized the 20th century.

Crowley found that gas and dust from volcanic eruptions, plus changes in output from the sun, could explain much of the climatic variability until the 20th century. But warming since "is only consistent with greenhouse gas forcing due to anthropogenic conditions," he said. That's science-speak for carbon dioxide emissions due to human activities.

He also works with his mathematician wife, German-born Gabi Hegerl, now an associate research professor at the Nicholas School's Earth and Ocean Sciences division. The pair met at Texas A&M, where she was visiting at the time. "She does statistical studies for detecting changes in climate," he said.

Crowley got his undergraduate degree at Marietta College in Ohio, where he was planning to major in history until he took a geology course. Geology "seemed as natural as drinking water," he said. So he took more courses and ultimately changed his major.

At Brown University, where he obtained his doctorate in 1976, he initially studied sediments and fossils to infer changes in ocean circulation. "That got me more interested in what caused those changes," he said.

After his doctorate, Crowley "took a break from science." For a year and a half, he taught college courses aboard U.S. Navy ships. He went back to his field in 1979 at the University of Missouri, where he worked with a well-known climate modeler.

After that, he directed the National Science Foundation's Climate Dynamics Program, became a research fellow at the NASA/Goddard Space Flight Center and was supervisor of the College Station, Texas, branch of a private consulting firm. Then he went to Texas A&M, where he became a professor of oceanography and deputy director of the Texas Center for Climate Studies.

"Some people somehow just naturally seem to like jumping and shifting into new areas," he explained.

At Duke, he plans to teach a new introductory level class on climate change in the spring (2002) and a graduate level course on paleoclimatology in the fall of 2002. On the research front, he plans to develop a "very interdisciplinary type of science" that combines modeling with the latest knowledge of physics, chemistry and biology "to simulate actual sedimentary sequences through time.

"What I'd like to do is help develop one of the next special areas of focus in the department," he said.

"I would also like to get involved in studying the effects of rising sea levels on barrier islands and coastal ecosystems, such as the North Carolina Outer Banks."

Monte Basgall is senior science writer in Duke's Office of Research Communications.