Abstract: Soil carbon stocks have the potential to be a strong source or sink for carbon dioxide over the next century, playing a critical role in climate change. Yet there was little agreement on soil carbon stocks between 11 Earth system models in the Climate Model Intercomparison Project 5. Predicted present-day stocks ranged from roughly 500 Pg to over 3000 Pg and predicted changes over the 21st century ranged from -70 Pg to +250 Pg. Why do such large differences exist between the models and are they all right?
Examining the codebase for all Earth system models was intractable. Instead, we fit a simplified model to Earth system model simulation outputs based on underlaying documented mathematical structure and initialization routines. We were able to explain most of the underlaying simulation behavior using this reduced complexity model. In general, model differences were explained by different in parameterization and inputs (mass and temperature), not underlaying structure. Furthermore, this variation reflects real world uncertainties in our observations, implying that the soil carbon response to climate change is extremely uncertain over the next century.
But are these models even right? Is the implicit process representation in these Earth system models correct? And if so, how can we connect them to a more explicit process understanding?
Bio: Kathe Todd-Brown is a computational biogeochemist who uses mathematics and computers to understand how soil breathes. She is an Assistant Professor at the University of Florida in the Department of Environmental Engineering Sciences. She received her PhD from the University of California, Irvine from the Earth System Science Department and holds a Bachelor of Science in Mathematics from Harvey Mudd College.