HR: 14:00h
AN: B23A-01    [Abstracts]
TI: Fire, drought, and feedbacks between the carbon cycle and the climate system
AU: * Randerson, J T
EM: jranders@uci.edu
AF: Department of Earth System Science, University of California, Croul Hall, Irvine, CA 92697, United States
AU: Tosca, M
EM: mtosca@uci.edu
AF: Department of Earth System Science, University of California, Croul Hall, Irvine, CA 92697, United States
AU: Flanner, M G
EM: mflanner@uci.edu
AF: Department of Earth System Science, University of California, Croul Hall, Irvine, CA 92697, United States
AU: van der Werf, G
EM: guido.van.der.werf@falw.vu.nl
AF: Faculty of Earth and Life Sciences Vrije Universiteit , De Boelelaan 1085, Amsterdam, 1081 HV, Netherlands
AU: Lin, H
EM: hwlin@uci.edu
AF: Department of Earth System Science, University of California, Croul Hall, Irvine, CA 92697, United States
AU: Collatz, G J
EM: jcollatz@biome2.gsfc.nasa.gov
AF: NASA Goddard Space Flight Center, Biospheric Sciences Branch Code 614.4, Greenbelt, MD 20771, United States
AU: Kasibhatla, P
EM: psk9@aerosol.env.duke.edu
AF: Nicholas School of the Environment, Duke University, Room A355, Levine Science Research Center, Durham, NC 27708, United States
AU: Zender, C S
EM: zender@uci.edu
AF: Department of Earth System Science, University of California, Croul Hall, Irvine, CA 92697, United States
AU: Giglio, L
EM: louis_giglio@ssaihq.com
AF: Science Systems Applications, Inc., 10210 Greenbelt Road, Suite 600, Lanham, MD 20706, United States
AB: We assess how humans have changed the magnitude (and possibly the sign) of interannual variability of atmospheric carbon dioxide. Remote sensing and trace gas observations from the last decade show that humans take advantage of El Nino-induced drought to clear tropical forests for agriculture at a faster rate. During El Nino events of 1997/1998, 2002, and 2006 fire emissions increased substantially in equatorial Asia. In parallel, fire-emitted aerosols may have reduced light levels and gross primary production at a regional scale. Both of these mechanisms contribute to a strong negative correlation between the Southern Oscillation Index and the CO2 growth rate observed in the Mauna Loa CO2 time series. In the absence of widespread changes in the fire regime caused by humans, two mechanisms linked with El Nino probably have the opposite effect on atmospheric carbon dioxide levels. In intact forests, moderate drought may enhance net ecosystem carbon uptake by causing microbial respiration to shutdown more rapidly than net primary production. Relaxation of the trade winds during El Nino suppresses upwelling and reduces outgassing of CO2 from the eastern equatorial Pacific - strengthening the ocean sink. Based on the differences between the anthropogenic and background terrestrial ecosystem and ocean responses to El Nino, we hypothesize that the sensitivity of terrestrial carbon loss to El Nino events will strengthen in the future with increasing demand for agriculture in tropical regions. More generally, the direct effect of climate on deforestation processes and agricultural productivity represents an important class of feedbacks between the carbon cycle and the climate system that is not yet represented in contemporary models.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 1615 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 4805, 4912)
DE: 1632 Land cover change
SC: Biogeosciences [B]
MN: 2007 Joint Assembly