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SUMMARY:Future methane\, OH\, and their uncertainties. - Dr Christopher D 
 Holmes\, University of California\, Irvine
DTSTART:20120417T150000Z
DTEND:20120417T160000Z
UID:TALK37490@talks.cam.ac.uk
CONTACT:Dr Alex Archibald
DESCRIPTION:Methane and hydrofluorocarbons (HFCs) are chemically reactive 
 greenhouse gases whose future atmospheric abundances will change as a resu
 lt of socioeconomic and climate forces. Accurate projections of these clim
 ate forcing agents requires knowing the sensitivity of their abundances to
  emissions\, meteorological factors\, and chemical feedbacks. Uncertaintie
 s in each of these processes implies uncertainty in future methane and HFC
  abundances and their radiative forcing. We conduct simulations of methane
  lifetime over the last 15 years in several atmospheric chemistry and tran
 sport models (CTMs) and use sensitivity tests to determine the key process
 es controlling interannual variability in these models. Across several CTM
 s (UCI CTM\, GEOS-Chem\, Oslo CTM3) we find that temperature\, water vapor
 \, biomass burning\, and lightning NOx are the dominant sources of year-to
 -year changes in methane lifetime. We also evaluate the model responses to
  forcings that change on slower time scales\, such as methane feedback\, a
 nd anthropogenic emissions magnitude and location. From the range of CTM r
 esponses\, we construct a parametric model for future methane and OH that 
 includes their uncertainties. We show that this simple parametric model is
  consistent with the ensemble spread from the Atmospheric Chemistry and Cl
 imate Modeling Intercomparison Project (ACC-MIP). This parametric model pr
 ovides a foundation for methane and HFCs along multiple socioeconomic and 
 climate trajectories.
LOCATION:Unilever Lecture Theatre\, Department of Chemistry
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