Where Has All the Carbon Gone? Atmospheric CO2 Assimilation in the GOSAT Era
Scott Denning, Colorado State University
Monday, November 2, 2009
4:00 p.m., 223 Weber
Nearly half of the CO2 from fossil fuel combustion is sequestered by poorly understood processes that may not persist in coming decades.
The future behavior of these "carbon sinks" is among the leading sources of uncertainty in future climate, because coupled models disagree on the strength (and even the sign!) of the carbon-climate feedback. Variations in the mixing ratio of atmospheric CO2 contain information about the distribution and behavior of carbon sinks in the recent past, and can be quantitatively interpreted using inverse modeling and data assimilation.
We have developed a system to predict global variations of atmospheric
CO2 at mesoscale resolution in near-real time, and to diagnose sources and sinks using ensemble data assimilation. Forward model components include terrestrial photosynthesis, respiration, and decomposition; fossil fuel combustion; biomass burning; air-sea gas exchange; and atmospheric transport driven by NASA GEOS-5 weather analyses. The system is evaluated using synthetic data from an orbital sensor of clearsky column CO2 in combination with in-situ data. Source/sink variations are decomposed into well-understood "fast" processes simulated by the forward model and poorly-understood "slow" processes that are estimated from the data. Given realistic coverage and error statistic from satellite observations, the system is very successful at recovering the distributions of regional sources and sinks.