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Eye On the Storm




How did you get interested in meteorology?

Shepherd: I was always interested in science generally, even as a small child. I first wanted to be an entomologist, but then I discovered—the hard way—that I was allergic to bees. So I began looking at other fields. By about the sixth grade, I knew that meteorology was it. I built all my own weather instruments and knew how they worked.

Tell us a little about the NASA-funded study you published last summer, which showed that the effects of big-city phenomena such as air pollution and urban land use extend well beyond the city.

Shepherd: We now have clear evidence that cities both create and alter rain events. The combined effect of the urban heat island, wind-altering buildings, and air pollution is the likely culprit, but the relative contribution of each component is still being studied. We’re also looking at how cities affect surrounding areas, and the answers have implications for weather forecasting, for agriculture, for emergency planning—say, to deal with or prevent floods—and for how you design future cities. By 2025, 60 percent of the population will live in cities, and the environmental effects will be even greater. So this kind of research has major societal consequences, which is also why it’s very important to me.

How do you study the links between precipitation changes and air pollution, and what have you learned?

Shepherd: Satellites measure global rainfall, clouds, and aerosols such as soot and other pollutants, and I study the relationships and trends among these variables and then model the processes. For example, there’s a debate among scientists about how urban pollution affects rainfall. In research I recently conducted at NASA with a University of Maryland colleague, we used a combination of satellite measurements to show that urban aerosols and clouds may peak at mid-week—because of human activities—and possibly increase the likelihood of rain. Future observational and modeling studies will be required to provide more conclusive evidence, but we now have the tools to study such problems, locally and globally.

Temperature records and computer models suggest that the globe’s warming climate will generate more powerful tropical storms in the years ahead. But your recent review paper on the subject says the scientific community is deeply divided over the meaning of the available data. Why the disagreement?

Shepherd: We know from theoretical model projections that in a warming climate—and we are now 0.6 to 1.6 degrees C warmer—that tropical storms should be stronger. When the oceans warm, their “fuel supply” is greater. Worldwide, more intense storms have in fact been more frequent, but whether that’s part of a natural cycle or human-caused is a point of contention. A second part of the debate is that our observational studies of storms go back only about 30 years—not very long-range, and not enough for us to make definitive statements. A third caveat is that other factors are also in play, like La Niña and El Niño. It’s clear to me that humans are a factor, but to what extent, we haven’t yet determined.

The most recent statement from the Intergovernmental Panel on Climate Change (IPCC)—that scientists are “90 percent certain” that humans are to blame for the warming climate—was confusing. What does it mean, and what do you as a climate-change re-searcher think about the IPCC report and process?

Shepherd: The IPCC process is the most definitive way we have of coming to consensus on current and future effects of climate change, though some scientists believe the report doesn’t go far enough and others think it goes too far. Meanwhile, even the skeptics are now acknowledging the human influences on climate, given the overwhelming body of scientific evidence. But while the models have become more and more reliable, they are not perfect. They still have some uncertainty, and the report reflects it.

Still, the panel did make some unequivocal statements this time around about long-range trends such as warmer average temperatures, fewer colder days and nights, stronger and more frequent storms, and heavier rain events. Humans are almost certainly affecting the strength and frequency of hurricanes, but we scientists need to provide definitive models that show not only what’s happening but also how it translates into specific outcomes. For example, if you look at the Arctic areas, where changes are already affecting polar bears and other wildlife, and hence the people who depend on hunting to live, climate change is very real.

What does climate change mean for the average person, though, and do you believe policy and personal lifestyle changes can slow down or eliminate its effects?

Shepherd: Climate change affects the average person every day—and that will continue, I’m sad to say, far into the future. Do I believe the sky is falling? No. Do I believe the average person’s lifestyle will be altered if there’s a 2-degree change in average temperature? Absolutely. But we also know that we can modify the trends as society embraces hybrid cars, integrates biofuels, uses low-energy light bulbs and makes other changes, large and small. In fact, we have a good example to go by—the ozone hole, which was caused primarily by chlorofluorocarbons [CFCs]. The Montreal Protocol severely limited the distribution and use of CFCs, and the result will be that in 20 to 30 years, the hole in the ozone will probably start to fade. And there are many other examples of how we can change the direction we’re now headed, especially the urban effects on climate change, by adopting more energy- and water-efficient city designs.

Contact J. Marshall Shepherd at

The Shepherd File

J. Marshall Shepherd, associate professor, Geography Department and Atmospheric Sciences Program, UGA

Hometown: Canton, GA; currently resides in Gwinnett County

Education: BS, MS, PhD in meteorology from Florida State University

Work history: Research meteorologist and deputy project scientist for the Global Precipitation Measurement (GPM) Mission, National Aeronautics and Space Administration (NASA); scientist, Goddard Space Flight Center, NASA

At UGA since: January 2006

Research: Climatology and meteorology, specifically the effects of urban areas on precipitation changes and hurricane hazards

Research funding: NASA, U.S. Department of Defense, National Science Foundation (pending)

Teaching: Introduction to Weather and Climate; Seminar in climatology; and Satellite Climatology

Family: Married to Ayana Shepherd; 3-year-old daughter, Arissa; son James, born April 19, 2007

Passions outside work: home theater; music (I have more than 1,200 CDs); playing tennis, golf, basketball; Scrabble; attending sporting events

Fan of: FSU, UGA

Recent book you’d recommend: Isaac’s Storm by Erik Larson

Weather Channel watcher? Yes, especially during hurricane season


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