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April 30, 2004
Land and Carbon: An Interview with Margaret Torn
Margaret Torn (Photo Roy Kaltschmidt)

Margaret Torn of Berkeley Lab's Earth Sciences Division warns that global warming is real, and we'd better prepare for it. Although her research has taken her to the steppes of Russia, the volcanoes of Hawaii, the tundra of Alaska, and the plains and mountains of the continental U.S., she reminds us that climate change starts at home: how global warming impacts local ecosystems will have dramatic effects for us all.

Born in Southern California, Torn moved with her parents to Northern California's rural Marin County when she was 11. At the College of Marin she became interested in the interactions of humans and the natural environment; after transferring to the University of California at Berkeley, she received her B.S. with highest honors in 1984, her M.S. in 1990, and her Ph.D. in 1994.

In this interview Torn discusses the evidence for climate change, some likely consequences of global warming, and topics of current scientific research.

Is global warming real, or is it just something people are scaring us with, to get us to give up our cars?

Torn: There is now an overwhelming scientific consensus that human activities will cause climate change. There may be some small doubt as to whether climate change has already occurred, because it's a complex statistical problem — whether all the changes in weather across the globe add up to a true signal of global warming. The consensus is based on two different kinds of evidence: predictions of general-circulation climate models and observations of temperature profiles around the world — increases from the surface all the way up into the stratosphere.

Then you have all the anecdotal evidence. Glaciers are disappearing. The sea level has risen. The 1990s were the hottest decade — and 1998 was the hottest year — ever recorded.

Do we really have to worry? Sea-level rise, for example, seems like something from a science-fiction movie.

Torn: Coastal real estate is expensive in California, but in most of the world it's poor people who live in flood-prone areas near the coast. Poor people have fewer options and fewer resources; they will bear the burden disproportionately. It's not just a matter of building a little sea wall around Malibu. There are whole island nations in jeopardy.

A warming climate leads to melting glaciers, rising sea levels, and an increased risk of catastrophic fires.

Another striking example was last fall's wildfires in Southern California. [The "Fire Siege" of October 2003 took 24 lives, destroyed 3,710 homes, and blackened more than 750,000 acres.] Evan Mills of the Environmental Energy Technologies Division and I worked on a study linking global climate models with wildfire models put together by the state's Department of Forestry and Fire Protection. It showed that the predicted climate change for a doubling of atmospheric CO2 would lead to a doubling in the number of fires that escape initial suppression — which can go on to become catastrophic fires.

Norm Miller of Earth Sciences has confirmed early projections that one effect of warming in California will be earlier and faster snowmelt — which decreases the snowpack, thus our fresh water supply later in the summer, and increases the potential for flooding in the spring. You get more water when you don't want it, and less when you do.

Some 80 percent of California water storage is done for us by snowpack, not dams. That's what I call an ecosystem service, which we'll lose by changing climate. We haven't begun to probe how many of these ecosystem services will be affected.

How about the notion that more CO2 could be beneficial to agriculture? That everything's going to grow faster?

Torn: Yeah, things like Scotch broom, water hyacinth.... It's true that invasive species and pests often do better in disturbed environments.

As temperatures rise globally, many kinds of plants and animals move toward the poles and to higher altitudes. Some alpine species will become extinct.

The most optimistic scenario is that plant and animal species will migrate toward the poles and uphill. That's optimistic unless you happen to be an alpine species and get squeezed off the top of the mountain. It's probably true that the wheat belt can expand into Saskatchewan, and that will be for a time beneficial. But the range of malaria mosquitoes and agricultural pests will also expand. A lot of them are kept in check by cold.

Tell us something about your current research.

Torn: In Oklahoma we're concentrating on the complicated problem of measuring and keeping track of CO2 concentrations in the air over continents. We're working with the Department of Energy's Atmospheric Radiation Measurement program in the Southern Great Plains to understand the influence of the land surface on the global CO2 levels that are forcing climate change.

For DOE we're also studying how plant-growth allocation affects how much carbon ultimately gets stored in soils. When a soil nutrient like nitrogen is limiting, plants may allocate more growth to roots; if light is limiting, they may allocate more above ground. Because we don't know much about what goes on below ground, people have tended to assume that roots cycle carbon just like leaves do. It turns out they don't, they're really different. Roots can become more stable organic matter.

Researchers are measuring changes in temperature and greenhouse gases over the central regions of the North American continent. (Photos Roy Kaltschmidt)

Most important, we're working to characterize the feedbacks between climate change and ecosystems — as sources and sinks of greenhouse gases, like CO2 and methane, and how the surface of the land affects things like albedo [reflectivity]. These are the key factors in radiative forcing, the basis of global warming.

We need to understand what things can change unexpectedly, given how quickly climate may change. And we need to learn how ecosystem processes may amplify the warming we have started. The time for prevention is now.

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