1. Estimates of global biogenic isoprene emissions from the terrestrial biosphere with varying levels of CO 2 David J. Wilton 1,2*, Kirsti Ashworth 2, Juliette Lathière 3, C. Nick Hewitt 2 and David J. Beerling 1 1 Department of Animal and Plant Sciences, University of Sheffield, UK; 2 Lancaster Environment Centre, Lancaster University, UK; 3 Laboratoire des Sciences du Climat et de l'Environnement, Gif-sur-Yvette, France * Email : d.j.wilton@shef.ac.uk Total Annual VOC Emissions (Tg C yr -1 ) Calculated without (and with) CO 2 suppression on isoprene The Eocene climate produces higher emissions Effect of CO 2 level on isoprene emissions, Eocene 4xPI climate Isoprene emissions for the Eocene remain high unless we include the effect of CO 2 suppression and have a much higher CO 2 concentration. References [1] Guenther, A. et al, Atmos. Chem. Phys, 6, 3181-3210, 2006 [2] Guenther, A. et al, J. Geophys. Res. Atmos, 100, 8873-8892, 1995 [3] Beerling, D.J. & Woodward, F.I. (2001) Vegetation and the terrestrial carbon cycle. Cambridge University Press. [4] Possell, M. et a, Global Change Biology, 1, 60-69, 2005 Acknowledgements We thank the Natural Environment Research Council for funding, Andy Fox and Paul Valdes (BRIDGE) for data. Climate Model PIEocene 2xPI CO 2 Eocene 4xPI CO 2 Isoprene8232780 (1386)5226 (1286) Monoterpenes80277457 Introduction A variety of volatile organic compounds (VOCs) are produced and emitted by terrestrial ecosystems at the global scale that have a substantial impact on atmospheric chemistry. Estimates of above canopy fluxes of isoprene and monoterpenes are required for quantitative Earth system studies, and particularly atmospheric chemistry models used to assess changes in tropospheric ozone and secondary aerosol formation with past and future atmospheric CO 2 regimes and climates. Here, we focus on the Earth system during the ‘greenhouse’ world of the Eocene, 50 million years ago and report a CO 2 sensitivity analysis and comparison of global annual isoprene and monoterpene emissions for a pre-industrial (PI). Methodology We use an emission model for isoprene based on MEGAN (Model of Emissions of Gases and Aerosols from Nature) [1] adapted to take account of the suppression of isoprene emissions by atmospheric CO 2 and a model for monoterpene emissions based on [2]. The Sheffield Dynamic Global Vegetation Model and the Hadley Centre ocean-atmosphere generation circulation model provide the inputs [3]. We compare results from a pre-industrial climate (CO 2 = 280 ppm) with early Eocene climates at 2x and 4x PI CO 2. Isoprene and monoterpene emissions are calculated, varying CO 2 for the former based on the equation from [4]. The CO 2 concentration in the Eocene is uncertain, but was much higher than modern levels and high CO 2 is known to suppress isoprene emissions. We consider the effect of CO 2 and climate on total annual emissions of the VOCs as well as the distribution of plant functional types. Conclusions The higher CO 2, warmer Eocene climate enhances emissions of VOCs, even when the effect of CO 2 suppression is taken into account. In particular, we can report substantially higher emissions of monoterpenes in the Eocene from far northerly and far southerly latitudes, as the climate allowed significant plant cover in these regions. These emissions can be used to derive estimates of secondary aerosol production which can in turn feed back in to the climate model. Work on this is in progress. Comparison of emissions and vegetation calculated for different climates Pre-Industrial Eocene 4xPI CO 2 Sea Bare C3 grass Evergreen Needle leaf Deciduous Broad leaf Evergreen Broad leaf Deciduous Needle leaf Isoprene Emissions / Tg yr -1 Monoterpene Emissions / Tg yr -1 Distribution of Major Plant Functional Types