Daniel Jacob (PI)
Harvard University
djj@io.harvard.edu

Investigation of the Effects of Land Cover Change on Chemistry-Climate Interactions

Future land cover change may have a large impact on the concentrations of aerosols and tropospheric ozone, with consequences for air quality and climate. We propose to quantify for the first time this indirect radiative effect of land cover change caused by land-driven perturbations to atmospheric chemistry, including changes in biomass burning frequency, biogenic emissions, dust mobilization, mixing depths, and dry deposition. Our approach will involve coupled ozone-aerosol simulations with the GEOS-CHEM chemical transport model, driven by archived meteorological fields from the GISS general circulation model (GCM), in future climate change scenarios including changes in land cover. We will implement a fire prediction scheme in the GISS GCM to simulate fire response to climate change. We will perform transient climate simulations for 2000-2100, using present-day vegetation and increasing greenhouse gases according to IPCC scenarios. Meteorological fields archived from this simulation will be applied to the Lund-Potsdam-Jena Dynamic (LPJ) vegetation model to generate land-cover change over the 21st century.  Peter Levy will supply previously published land-cover trends from the Hyland model for the same time period.  We will examine the consistency of the calculated present-day vegetation maps with observations from the MODIS satellite instrument. To describe the effect of land-cover change on meteorology, we will implement these calculated vegetation maps into the GISS GCM, and recalculate the 2000-2100 climate. We will then perform a series of ozone-aerosol GEOS-CHEM simulations at 25-year intervals from 2000 to 2100, applying GCM meteorology, land-cover projections from the LPJ and Hyland models, and the calculated trends in forest fire projections. Results will be compared to a control GEOS-CHEM simulation driven by the GISS GCM transient climate simulation for 1950-2100 including present-day vegetation. Differences between the two simulations will diagnose the changes in ozone and aerosols due to land cover changes. From there we will calculate the indirect radiative forcing from land cover change associated with this atmospheric chemistry effect, and if this forcing is significant we will examine the climate response.

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