HR: 1050h
AN: B52C-03    [Abstracts]
TI: Can we reconcile our understanding of the atmospheric methane budget over the past decades with atmospheric observations?
AU: * Bruhwiler, L M
EM: lori.bruhwiler@noaa.gov
AF: NOAA GMD/ESRL, 325 Broadway, Boulder, CO 80305, United States
AU: Matthews, E
EM: ematthews@giss.nasa.gov
AF: NASA GISS, 2820 Broadway, New York, NY 10025, United States
AB: The balance of methane in the atmosphere is determined by surface emission, and losses due to uptake in soils and reaction with the hydroxyl radical. The atmospheric abundance of methane has risen by about a factor of three since pre-industrial times, but the growth rate has decreased substantially since the 1990's. Thus, global atmospheric methane appears to have equilibrated to around 1780 ppb subject to considerable interannual variability, the causes of which are not well-understood. Methane emissions are expected to increase in the future due to increases in fossil fuel use and possible changes in wetlands at high-latitudes, and it is therefore important to test our understanding of the methane budget over the last two decades against network observations of atmospheric methane. Issues of interest are whether we can match the rise in methane over the 1980's, whether we can explain the decrease in growth rate during the 1990's, and whether we are able to simulate the observed interannual variability in the observations. We will show results from a multi-decade model simulation using analyzed meteorology from the ERA-40 reanalysis over this period. New times series of methane sources for 1980 through the early 2000's are used in the simulation. Anthropogenic sources include fossil fuels with a total of 7 fuel-process emission combinations associated with mining, processing, transport and distribution of coal, natural gas and oil; ruminant animals and manure based on regionally-representative profiles of bovine populations ; landfills including the impact of on- site methane capture; and irrigated rice cultivation based on seasonal rice-cropping calendars. Natural sources we include are biomass burning from the GFED emission data base, oceans, termites, and natural wetlands using a multiple-regression model derived from a process-based model. If time permits, we will also show preliminary results of a methane data assimilation using the Cooperative Air-Sampling and GMD network observations, and our new estimates of methane sources.
DE: 0315 Biosphere/atmosphere interactions (0426, 1610)
DE: 0365 Troposphere: composition and chemistry
DE: 0426 Biosphere/atmosphere interactions (0315)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting