CSU Physics Colloquium

SOURCES AND SINKS OF CO₂ DEDUCED FROM ATMOSPHERIC GASES

Dr. Scott Denning

Colorado State University

Mon,  10/12

Only about half of the CO₂ released by combustion of fossil fuels accumulates in the atmosphere. The rest is absorbed by dissolving into the oceans and by the net accumulation of organic material on land. Net land uptake was quite unexpected, is not well understood, and may not persist, yet is one of the few parts of the global carbon cycle amenable to management.

To better understand the mechanisms and distribution of CO₂ sources and sinks, we extract quantitative information about them from tiny but well-measured variations in the CO₂ concentration in the overlying atmosphere. This requires careful accounting for transport processes in the atmosphere, which is done with numerical models. The problem of inverting the observed concentrations is badly underconstrained, so we must also use a lot of other data, such as vegetation imagery from satellites, agricultural and forest inventories, fossil fuel emissions estimates, and ocean observations.

We find that much of the net land uptake occurs in the middle latitudes of the Northern Hemisphere, and that within North America the budget varies a lot from year to year because of climate variations (e.g., droughts). For 2004, we find that net uptake was especially strong in the south-central USA, associated with unusually heavy rains over managed forests in that region.