Inez Fung, University of California, Berkeley

Research Objectives

Paleo and historical records have shown that the concentrations of CO₂ and other trace species have co-varied with climate fluctuations on interannual to glacial-interglacial time scales. This research focuses on the mutual interaction between the carbon cycle and climate. It investigates how the terrestrial and oceanic carbon reservoirs may sequester or outgas CO₂ as climate changes, and hence determine the CO₂ abundance in the atmosphere. It explores how the rates of atmospheric CO₂ increase and climate change co-evolve and feed back on one another.

Computational Approach

The global three-dimensional Climate System Model (CSM) of the National Center for Atmospheric Research (NCAR) is the principal tool. Fully interactive atmospheric, terrestrial, and oceanic carbon modules are implemented in the physical climate model. Three experimental themes are envisioned. The first focuses on the interannual variations of CO₂ since the 1980s, and attempts to simulate and explain the CO₂ growth rate variations observed. The second explores how climate change may alter terrestrial and oceanic carbon sinks, and the implications of these changes for achieving a target CO₂ level in 2050. The third prescribes a fossil fuel emission scenario, and lets the prognostic and fully interactive carbon and climate system co-evolve. Key to the analysis within each theme will be the sensitivity experiments that capture our confidence in and ignorance about carbon processing and how it may interact with climate.

The three-dimensional distribution of a hypothetical inert surface tracer through time demonstrates the pathways this tracer uses to go from the surface into the deeper ocean. The model was run for 50 years; this frame shows the values of the passive tracer at the 11th vertical level.

Accomplishments

In the past year, we ran the atmospheric and oceanic modules of CSM, and because of our interest in the dispersal of CO₂ in the atmosphere and the ocean, we focused our analysis on the distribution of hypothetical inert surface tracers in the models. The three-dimensional distribution of the tracers through time clearly demonstrates the different circulation regimes between the Atlantic and Pacific oceans. The penetration of the tracer in the North Atlantic and the transport by the North Atlantic deep water is evident in the movie made with model output by the NERSC Visualization Group using AVS software. The results contribute to our understanding of how anthropogenic CO₂ may have penetrated the oceans, and to our evaluation of the ocean's capacity to store CO₂. We also used the NERSC Visualization facility to display the dispersal of anthropogenic CO₂ in the atmosphere. The results are crucial to the inversion calculations needed to infer the locations and magnitudes of the terrestrial and oceanic carbon sinks.

Significance

This work will provide scientific input to national and international policy decisions about the feasibility of and strategy for managing the CO₂ level in the atmosphere. It complements the DOE's new focus on carbon sequestration.

Publications

J. T. Randerson, C. B. Field, I. Fung, and P. Tans, "Increases in early season ecosystem uptake explain changes in the seasonal cycle of atmospheric CO₂ at high northern latitudes," Geophys. Res. Lett. (in press).

J. T. Randerson, M. V. Thompson, T. J. Conway, I. Fung, and C. B. Field, "The contribution of terrestrial sources and sinks to trends in the seasonal cycle of atmospheric carbon dioxide," Global Biogeochemical Cycles 11, 535 (1997).

I. Fung, C. B. Field, J. A. Berry, M. V. Thompson, J. T. Randerson, C. M. Malmstrom, P. M. Vitousek, G. J. Collatz, P. J. Sellers, D. A. Randall, A. S. Denning, F. Badeck, and J. John, "Carbon-13 exchanges between the atmosphere and biosphere," Global Biogeochemical Cycles 11, 507 (1997).

http://www.atmos.berkeley.edu/ifgroup/