Volume 3, Issue 18 February 2006
From Carbon Cycles to Climate Models
In November of last year, Inez Fung won a Scientific American 50 award, recognizing leadership in shaping science and technology.
While we go about our daily lives, our planet's atmosphere—land, oceans, and ice—are interacting in an incredibly complex dance. The Earth is a closed system, where these subtle interactions have a global impact on the climate. UC Berkeley professor Inez Fung constructs incredibly complex computer simulations of the climate. By uncovering the myriad forces behind climate change, Fung's research is revealing how our actions today may have dire consequences for the world of tomorrow.
Scientists have long known that the Earth is getting warmer, explains Fung, a professor in the Department of Earth and Planetary Science and Environmental Science, Policy, and Management. This warming is tied to changes in the Earth's atmosphere, specifically the increase of carbon dioxide and other greenhouse gases. The gases trap energy from the sun so that it warms the surface of the planet. Enhancing the greenhouse affect, through the burning of fossil fuels for instance, changes the energy cycle, leading to global warming.
"There's a rogues gallery of these atmospheric species, greenhouse gases like carbon dioxide and methane, that affect the energy cycle and climate," says Fung, co-director of the new Berkeley Institute of the Environment and former director of the Berkeley Atmospheric Sciences Center. "I'm hitting them one-by-one to understand what determines their concentration in the atmosphere, why that's changing, and how."
Fung's experiments take place inside interactive mathematical simulations, what she calls "huge, monster climate models" that can take weeks or months to run on the world's fastest supercomputers. Some of the data that's fed into the simulations come from atmospheric field observations, actual information gathered about the climate at a particular moment. The trick though is modeling how those inputs change.
Most famously, Fung and her colleagues modeled the carbon cycle, how carbon dioxide moves in and out of the atmosphere. Previous calculations included the fact that humans burning fossil fuel at a certain rate will boost carbon dioxide levels in the atmosphere.
"That just a forcing function though," Fung says. "To really understand the carbon cycle, you have to look at the circulation, biology and chemistry of the oceans where the carbon dioxide goes, the photosynthesis of plants as they breath carbon dioxide, the decomposition of plants, and many other forces."
A graphic depiction of the Earth's carbon cycle, highlighting various sources and sinks for carbon. (courtesy the researcher)
More than 15 years ago, Fung's atmospheric model suggested that the land biosphere, in addition to the oceans, have been acting as carbon sinks, repositories for the fossil fuel carbon. Fung's model "prediction" has since stimulated new programs in terrestrial ecology.
Indeed, Fung studies the whole shebang. Last month Fung, UC Berkeley integrative biologist Todd Dawson, and their colleagues, reported that trees are much more involved in carbon uptake and atmospheric cooling than previously believed. A study in the Amazonian forest showed that the roots shift water deep in the ground in such a way that they "pull more carbon dioxide from the atmosphere as they conduct more photosynthesis" even during the dry season, Dawson says.
The trouble is that there's a limit to how much carbon dioxide the world's plants can handle. Right now, plants and oceans absorb about half of the CO2 that's generated from the burning of fossil fuels. Last year, Fung's climate model indicated that in the next fifty years or so, the "breathing biosphere" may be overwhelmed.
Not only is there a metabolic limit to the process, but during periods of drought caused by a warming climate, the plants breathe less in an effort to save water. This affects the levels of CO2 in the atmosphere, creating a feedback loop in the system. And after plants die, their decomposition by microbes in the soil also play a part in the carbon cycle.
"If you don't look at decomposition, it's like looking at your income without considering your expenses," Fung says. "You have to think about the whole life cycle across the entire biosphere."
Simultaneously, the oceans' capabilities as a CO2 sink are hampered. Normally, turbulence shifts the CO2 deep into the ocean where it can't be sucked up into the atmosphere. But as the climate warms, the ocean becomes more stratified, making it difficult for CO2 to be driven to the depths.
"From the biosphere to the oceans, the warming feeds the warming," Fung says.
The question is how much. If things continue as they are, the global temperature may increase by more than two degrees Fahrenheit in the next 50 years or so. The consequences of such an increase are not entirely predictable. Still, Fung says, the model indicates that if fossil fuel CO2 emission is reduced, the plants and oceans could continue to support the carbon cycle as it currently exists.
"I'm not a policy maker, but I think my research could influence policy decisions, and personal decisions, about the kind of future we want," Fung says.