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Carbon Hunter

Profile: Inez Fung, University of California at Berkeley -- by Seth Shulman

Inez Fung

Inez Fung, director of the Berkeley Institute of the Environment at the University of California, Berkeley, is on a mission to ferret out and account for every gram of heat-trapping carbon dioxide on the planet. And she knows where most of it is hiding. Fung's work has led to a more complete understanding of the current and future role played by Earth's so-called "carbon sinks"— features such as oceans and forests that suck carbon dioxide out of the air. Her research shows that when the role of these carbon-absorbing mechanisms is taken fully into account, global warming is likely to accelerate even faster than scientists previously believed.

Of course, scientists' direct measurements of the atmosphere over the past half century show clearly that concentrations of carbon dioxide are rising and causing the planet to warm. So why study carbon sinks? Because the planet's ability to absorb carbon dioxide is a vital and tricky part of the climate-change equation. Up until now, Earth's land, vegetation, and oceans have soaked up roughly half of all the heat-trapping CO2 we have emitted by burning fossil fuels. Fung's research analyzes whether the carbon sinks can keep pace with today's unprecedented levels of CO2 emissions. The stakes are high, because any reduction in the Earth's ability to absorb CO2 could dramatically increase the swiftness and severity of global-warming processes now underway.

As high as the stakes may be, the planet's so-called "carbon dynamics" are tough to master, requiring a detailed knowledge of everything from atmospheric transport models to the mechanics of photosynthesis. Luckily, Fung is well suited to the task.  The key to her approach lies in her training in mathematics and her penchant for tackling big problems, both of which she honed early on.

Fung says she has loved math since she was a kid. "It's no doubt irksome to some people," she says, "but I see everything through the lens of mathematics." She graduated from MIT with a degree in applied math, and when she decided to stay there to do graduate work, she took the field of meteorology by, well, storm, using math and fluid dynamics to explain the spiral shape of hurricane rain bands. She says weather had long fascinated her. As a child growing up in Hong Kong, she looked eagerly to the harbor for the lights placed there to indicate an impending typhoon. "Of course, back then," she says, "we were mostly excited about this because it meant school would be canceled."

After grad school, Fung joined a climate-modeling team led by the well-known climate scientist James Hansen at NASA's Goddard Institute for Space Studies at Columbia University in New York. It was there, she says, that she started thinking in earnest about Earth's carbon cycle. It seemed obvious to her that carbon sinks had to be included in any analysis of climate change. Without that factor, she says, the results would be as incomplete as "trying to make a budget by looking at your income without considering your expenses."

Fung says she started learning about carbon sinks on her own, from scratch. She married Jim Bishop, a marine chemist, and she and her husband often went on camping trips with other scientists. On hikes and around the campfire, she would regularly buttonhole colleagues to learn everything she could about arcane aspects of the science of the carbon cycle, often taking notes on what they told her. Before long, she says, she determined that Earth's uptake of carbon "could be reduced to seven equations with seven unknowns."

Fung's analysis derives from the fact that there are a finite number of major types of carbon sinks. Researchers know that the oceans absorb heat-trapping CO2 from the atmosphere as surface water mixes with air and seeks equilibrium. CO2 dissolves into the sea water and converts to a form that marine creatures are able to incorporate into their shells. These creatures are recycled through the food chain, and decomposition of their sinking detritus converts the organic material back into inorganic minerals. Wind and ocean currents then deliver this rich supply of nutrients and minerals to the surface to fuel photosynthesis. A very small fraction of their shells fall to the bottom of the ocean and eventually build up sediment that forms carbonate rocks, which can hold carbon atoms on the sea floor for millions of years. On land, meanwhile, plants take in CO2 and, using photosynthesis, turn it into carbohydrates that are stored either in leaves, trunks or in the root systems of trees.  When leaves fall or when plants die, microbes in the soil decompose the plant detritus and return the CO2 to the atmosphere.

Before Fung's work, most scientists studying the carbon cycle had focused on one or another specific mechanism, such as the ecophysiology of the leaves of a particular tree. As valuable as that research is, Fung says, it is too fine-grained for her purposes. As she puts it, "If you sit in one spot it's hard to extrapolate to another, like trying to determine how the economy is doing by looking only at one corner store."

Instead, Fung opted for a global approach. Thinking about the whole carbon cycle across the entire biosphere, she and her team started to take apart the regular measurements of carbon dioxide in the atmosphere at locations around the world. The increasing overall levels of CO2 grab all the headlines, but Fung focused on the seasonal fluctuations evident in the data. Concentrations of carbon dioxide in Earth's atmosphere reach their highest levels in May, before the growing season begins, when photosynthesizing by new foliage draws the levels down. "We look at these records in great detail," Fung explains, "to derive everything we can about the biosphere. It is like you can see the Earth breathing."

Before long, Fung's detailed data analysis helped her build a large-scale computer model to represent the geographic and temporal variations of CO2 sources and sinks. Many ecologists were not impressed at first, considering Fung's work oversimplified.  She has long since shrugged off her critics, especially as her research results have been increasingly borne out in observational data.  "Ecologists are understandably always committed to seeing physiognomic differences," Fung says. "Sure, we all look different. But I was looking at ecology on a global scale with the working hypothesis that the carbon has to go somewhere." As she says with a chuckle, "I started trying to build a working shack. There was no stained glass."

More recently, Fung has coupled her carbon-cycle model onto existing large-scale computer climate models to project how land and ocean carbon sinks are likely to change as global warming proceeds.  One major finding: droughts have already diminished the uptake of CO2 on land and will continue to do so.  Previous greenhouse experiments had indicated that increasing CO2  caused plants to grow more and faster, an effect known as CO2 fertilization. The implication was that land-based carbon sinks might be able to keep pace with higher CO2  levels. But Fung's modeling shows that on a global scale, regional droughts are likely to curtail this effect. Her model projects that the tropics are likely to become hotter and drier in the summer, for example. As that happens, plants will slow their ability to take in carbon dioxide to avoid water loss. In fact, atmospheric measurements over the past decade have already confirmed this effect. Fung says that her research shows that soil moisture is a key variable, and she worries that increasing regional droughts will further hasten warming trends.

Nowadays Fung's colleagues are paying close attention to her analysis. Her work is widely cited, and she has won many accolades, from attaining membership in the National Academy of Sciences to being named one of Scientific American's 50 most influential scientists in 2005. Her life and work are even the subject of an online comic strip aimed at middle schoolers.

In one of Fung's latest efforts, she is getting ready for a new satellite—the Orbiting Carbon Observatory (OCO-2)—expected to launch in 2013. OCO-2 will collect an unprecedented volume of data on the levels of heat-trapping CO2  in the atmosphere. As Fung explains, she will go from being able to draw upon roughly one hundred observations of near-surface CO2 concentrations every two weeks from remote locations around the world to a million observations over the same two-week period. In addition, OCO will be able to read CO2  levels of the entire atmospheric column, eliminating the need to guess the variations of CO2  at different altitudes, which can help target carbon sources and sinks. With OCO's help, Fung's "working shack" will gain, if not stained glass, at least a telescope.

Not surprisingly, Fung sees the tough policy choices that global warming presents as a complex math problem. "In considering something like climate change, the political arena has to weigh many, many variables, from economic to environmental considerations. In math we call this a weighting function, and it all depends on how you weigh these different variables. I don't know the best way to do that. What I do know is that my role is to offer the most accurate analysis I can of what is happening."

“Unfortunately,” Fung says, “I don’t think we scientists have done very well communicating the issues to the public. We do a lot of talking to one another. But I still haven’t seen any of my friends on Oprah yet. I’m afraid we are not broadcasting our findings on the right wavelength.”

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