Persad, Geeta, Xiaochun Zhang, and Ken Caldeira. “ Natural Gas and Carbon Intensity in the Transportation Sector: Compressed Natural Gas versus Battery Electric Vehicles”. Environmental Research Letters (Submitted). Print.Abstract

The current glut of domestic natural gas resources provides a potential fuel source for the U.S. transportation sector that could have environmental, economic, and national security benefits over traditional petroleum fuels. But what mode of natural gas powered transportation best meets domestic climate mitigation goals? Natural gas could be used either as direct fuel for dedicated compressed natural gas vehicles (CNGVs), or as feedstock for electricity generation to charge battery electric vehicles (BEVs). Using lifecycle analysis in the current national mix of natural gas power generation, we show that CNGVs produce more carbon dioxide emissions per kilometer driven than do BEVs sourced from the same domestic natural gas. BEVs powered by the current U.S. mix of natural gas generation emit 27% less carbon dioxide than CNGVs for a given distance driven, with even greater emissions reductions when BEVS are powered from combined-cycle natural gas generation only. These results suggest that current governmental support for investment in compressed natural gas fueling infrastructure may not be carbon optimal compared to investment in an electric vehicle charging infrastructure.

Persad, Geeta, Yi Ming, and V Ramaswamy. “Spatially Similar Surface Energy Flux Perturbations due to Greenhouse Gases and Aerosols”. Nature Communications (Submitted). Print.Abstract

Recent studies suggest that, despite distinct geographic distributions of top-of-the-atmosphere radiative forcing, anthropogenic greenhouse gases and aerosols give rise to similar patterns of climate response (though of opposite sign) in fully atmosphere-and-ocean coupled general circulation model simulations. The surface energy flux perturbation, a crucial pathway by which atmospheric forcing is communicated to the ocean, may be a vital link in explaining the spatial similarities in the full atmosphere-and-ocean responses to disparate forcings. We here analyze the fast, atmosphere-only change in surface energy flux caused by present-day greenhouse gases versus aerosols to elucidate its role in shaping the subsequent slow, coupled response. We find that, although the two forcings are largely uncorrelated under clear-sky conditions at the top-of-the-atmosphere, their surface energy flux perturbation patterns are significantly anti-correlated. Our analysis highlights the common modes of atmospheric circulation and surface energy adjustment that are triggered by both greenhouse gas and aerosol forcings. These produce antisymmetric (i.e. symmetric, but of opposite sign) spatial patterns of surface sensible and latent heat flux variations in response to the two forcers, particularly over the winter-hemisphere oceans. Our results suggest that atmosphere-only processes are capable of achieving substantial homogenization within a given hemisphere in the climate response to disparate forcers on fast timescales, with implications for detection and attribution and for the understanding and prediction of the regional climate impacts of anthropogenic greenhouse gases and aerosols.

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Persad, GG, Y Ming, and V Ramaswamy. “Tropical Troposphere-Only Responses to Absorbing Aerosols.”. Journal of Climate 25 (2012): , 25, 2471-2480. Web. Publisher's VersionPDF icon jcli-d-11-00122%2E1.pdf
Ming, Y, V Ramaswamy, and G Persad. “Two Opposing Effects of Absorbing Aerosols on Global-mean Precipitation.”. Geophysical Research Letters 37.L13701 (2010). Print.Abstract

Absorbing aerosols affect global‐mean precipitation primarily in two ways. They give rise to stronger shortwave atmospheric heating, which acts to suppress precipitation. Depending on the top‐of‐the‐atmosphere radiative flux change, they can also warm up the surface with a tendency to increase precipitation. Here, we present a theoretical framework that takes into account both effects, and apply it to analyze the hydrological responses to increased black carbon burden simulated with a general circulation model. It is found that the damping effect of atmospheric heating can outweigh the enhancing effect of surface warming, resulting in a net decrease in precipitation. The implications for moist convection and general circulation are discussed

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