Department of Environmental Sciences

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Seminar Abstracts
Environmental Sciences Seminar Abstract            

Nadine Unger
Yale University

The short-lived climate forcers (SLCFs) ozone, methane and aerosol particulates and their indirect effects on cloud properties significantly impact regional and global climate but in complex ways involving both warming and cooling mechanisms. Reducing precursor emissions of the SLCFs has the advantage of rapidly changing radiative forcing. Selective reduction of the warming SLCFs is currently receiving attention as a way of mitigating near-term warming, reducing the rate of warming (important for adaptation of ecosystems) and simultaneously improving air quality. Feedbacks from human land-use change via altered biogenic volatile organic compound (BVOC) emissions from vegetation have so far been neglected in historical assessments of the SLCFs. BVOC emissions profoundly alter atmospheric chemical composition and play an important role in the carbon cycle. The near balancing of the counteracting BVOC emission drivers, CO2 inhibition versus the effects of temperature and CO2-fertilization, implies that land-use change plays the critical role in determining changes to BVOC emission. In a first assessment that applies the NASA GISS global climate model (ModelE), it is shown that the biogenic secondary organic aerosol direct radiative forcing from the 1850 to 2005 cropland expansion may entirely counteract the biophysical (albedo) forcing from this land cover change (+0.16 versus -0.09 Wm-2). The land cover change alone implies a 15% longer methane lifetime in 1850 than 2005 while overall net effects on ozone forcing are small.

Last updated: 01/29/2012