Global atmospheric chemistry climate modeling

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Atmospheric chemistry might have played an important role in shaping the climate of the cenozoic era. For example, Sloan and Pollard (1998) explain the so-called "low gradient paradox" (high temperatures in high latitudes) by enhanced methane release from wetlands leading to increased water vapour in the stratosphere and ultimately to warming of the high latitude earth surface. Methane (CH4) is one of the most important greenhouse gases. Its lifetime is predominantly determined by hydroxyl (OH) radicals, so that CH4 both affects and is affected by the atmospheric oxidation (self-cleansing) efficiency. OH in turn is intimately linked to various atmospheric chemistry processes and budgets. Of particular importance are the budgets of NOx (reactive nitrogen species, NO and NO2), biogenic volatile organic compounds (VOCs), carbon monoxide (CO) and ozone. Natural emissions of CH4, NOx, CO and VOCs depend strongly on climatic conditions. In this work package we will estimate the natural emissions of these compounds and their uncertainties for the cenozoic climate. We will use them as input to a set of global atmospheric chemistry simulations in order to assess the strength of the chemistry climate feedback and the potential state of the atmospheric chemical composition under these conditions. The climatic conditions (including inter-annual variability), vegetation patterns and orography will be taken from WP1 and WP5 of this project. The global distribution of potential wetlands and their methane (CH4) emissions at the present-day and during the Cenozoic climate will be estimated using a process-based approach following Kaplan (2002) and Walter et at. (2001), respectively. Other biogenic emission sources and vegetation fires will be estimated via parameterized approaches (Guenther et al., 1995; Thonicke et al., 2001). Budgets of CH4 and global distributions of OH for various climate conditions will be calculated in multidecadal time slice simulations by a general circulation model, which includes a comprehensive representation of tropospheric chemistry.