Using recently assembled satellite images of the global land surface, Christopher Potter and Steven Klooster modeled the response of decaying plant matter to changes in temperature and precipitation patterns.

This dynamic computer model shows monthly changes for carbon dioxide released into the atmosphere as microbes decompose plant debris in the Earth's soil. A slight

Scientists from the Carnegie Institution and Stanford University collaborated with Potter and Klooster. The Carnegie Ames Stanford Approach (CASA) Biosphere model shows annual production of carbon dioxide from soils is 10 times that produced by fossil fuel emissions. The model shows that plants, however, absorb carbon dioxide in amounts equal to that produced by the soils, balancing the output.

The model also shows 60 percent of the carbon dioxide is produced and absorbed at tropical latitudes. Monthly inputs of climate and solar radiation and satellite data at a one-degree latitude/longitude resolution for the entire globe drive the model. Soil and vegetation types are also included as inputs.

The CASA model can be used to study how tropical deforestation and changes in land use affect emissions of atmospheric trace gases. It also can bring a better understanding of the role of forests and land-use change in global biogeochemical cycles.

The CASA model is also one of the first to simulate global soil emissions of nitrous oxide, another important greenhouse gas. We are also investigating the global impacts of fertilizer applications on greenhouse gas fluxes. A significant part of the nitrogen used in agricultural fertilizer ends up in the air, dramatically changing atmospheric concentrations of nitrous oxide. When it finds its way into the stratosphere, it also aids ozone depleting reactions.

Models like the CASA approach, which are verified by independent observations and continually refined, are an important element of NASA's Earth Science Enterprise (ESE). ESE focuses on understanding the links between large environmental systems, in this case land surfaces, atmosphere and climate. The goal of ESE is to collect, analyze and distribute data that will allow humans to make informed policy decisions about how their actions are affecting the global environment.