Connecting ecosystems to the atmosphere

Peter Thornton, Biogeochemist

Photo of Peter Thornton
Peter Thornton (Photo by Carlye Calvin, UCAR.)


Peter Thornton is now on the research staff of the Environmental Sciences Division of the Oak Ridge National Laboratory in Tennesse (April 2010).

A career in science has always felt natural to Peter Thornton, who realized as a child that he was drawn toward analytical tasks like programming his computer. "If I weren't working in science, I'd still be thinking the same way," he says. "It's like getting paid to do what my brain wants to do anyway."

One thing his brain clearly wants to do is take a highly interdisciplinary approach to science: Peter is a biogeochemist with training in ecology who focuses on climate. Biogeochemistry is the study of the biological, geological, and chemical processes that govern the composition of the natural environment, including the atmosphere. In particular, Peter looks at interactions between different biogeochemical species (such as carbon and nitrogen) and Earth's climate system.

His research contributes to NCAR's Community Climate System Model (CCSM), an advanced computer model that is the result of collaboration among hundreds of researchers in different fields related to atmospheric science. Scientists at NCAR and around the world use the CCSM to run simulations of Earth's past, present, and future climate, including projections of global warming based on the amount of carbon dioxide and other greenhouse gases in the atmosphere.

Peter's role is to help develop, test, and apply the model. Specifically, he's interested in interactions between the carbon cycle and the nitrogen cycle. "I'm trying to demonstrate the effect nitrogen has on the way the carbon cycle and climate system feed back on each other," he explains.

Previous studies have shown that land-based ecosystems respond to increasing atmospheric carbon dioxide concentrations by taking up more carbon, while also responding to increasing temperature by releasing carbon.

"These studies did not consider interactions between the carbon and nitrogen cycles," Peter says. "When carbon-nitrogen coupling is included, both the carbon uptake and release are reduced. We're working now to determine the global-scale consequences of these new interactions."

He especially enjoys the collaborative nature of working on the CCSM. "It involves lots of different people with deep expertise in particular aspects of the climate system and Earth system in general," he says. "Any one person can't have the level of expertise necessary to deeply understand the whole system, but when you work with a group like this you have people who understand just about every aspect of it in great depth. I feel really fortunate to be brought into this realm."

The most challenging part of his job is evaluating the model's performance, due to a shortage of real-world observations to use for comparison. Although people have been using instruments to record temperature and precipitation measurements for at least 150 years in some locations, scientists didn't start measuring landscape-scale fluxes of carbon dioxide until about 15 years ago. Currently there are only several hundred sites around the globe where such measurements are taken.

"There's not a long baseline of detailed measurements relating to the carbon cycle, and as we get into more details of interactions between carbon, nitrogen, and climate, there's not much information to start from," Peter explains.

Peter has always had an interest in the natural world, having grown up surrounded by farmland in rural western Pennsylvania. As a child, he was drawn to math, science, and computers. He recalls having a lot of encouragement from his parents and teachers.

"I was lucky enough to have good high school chemistry, physics, and calculus instructors. It all came together for me," he says.

After high school, Peter enrolled at Johns Hopkins University with the specific intent of majoring in biomedical engineering. "I knew that it was a mixture of math, science, and computer programming, and that it brought together biological aspects of science and a lot of physiological feedback systems," he says.

Although he enjoyed the coursework, he soon realized that neither medicine nor engineering truly appealed to him as a career. One day he was sitting in a modern literature class taught by a professor who was known for giving bewildering reading assignments that combined seemingly disparate authors. The discussion that day involved two readings.

World map with land areas in different colors
This map is an example of output from the carbon-nitrogen model that Peter has been developing. It shows plant growth around the globe, expressed in grams of carbon per square meter per year. (Illustration courtesy Peter Thornton, NCAR.)

The first was by the British scientist James Lovelock, who had recently published his Gaia hypothesis, in which he proposed that the living matter of planet Earth functions as a single organism through feedback systems that create optimal physical and chemical environments for life. The second reading was "The Library of Babel," arguably the best-known story of Argentine author Jorge Luis Borges. Borges' fantastical metaphor of a vast library containing every possible book that could be composed in a certain set of letters and punctuation marks has at times been compared to the complex system formed by Earth's biosphere.

The discussion that day stuck in Peter's mind. "It was the seed that got me thinking about the bigger picture, the idea of geophysiology, and the climate system," Peter recalls. He already knew that he was interested in modeling feedback systems and using analytical tools. He realized he could migrate the technical and analytical skills from his engineering background toward Earth system science. He decided to focus on terrestrial (land) ecology and biogeochemistry.

So Peter finished up his biomedical engineering degree and spent a summer participating in a field ecology program at Colorado State University, which convinced him to pursue a master's degree at Johns Hopkins that involved studying sediment cores from the Chesapeake Bay to determine sea-level rise over the past several thousand years. His next step was to the University of Montana, where he earned a doctorate through the College of Forestry and Conservation. As part of his thesis, he added the nitrogen cycle to a biogeochemical model of the terrestrial carbon cycle.

In 2001, Peter came to NCAR to join a group of researchers working on biogeochemistry for the CCSM. He finds that his "scattered background" in engineering, physiology, biology, and Earth science is an asset in his current role. "For Earth system modeling, it's helpful to have broad training, as opposed to exclusively focused, disciplinary training," he says.

In the future, Peter wants to extend his research beyond nitrogen to look at other biogeochemical species such as phosphorus.

He also has a longstanding interest in social impacts and public policy. "Once I've had what impact I can on model development, I see myself moving more toward model application and a policy perspective," he says. "The motivation, other than intellectual stimulation, is that climate change is an important problem. It's not just an academic pursuit, but a social, environmental, and political problem with all kinds of global consequences."


by Nicole Gordon
October 2006