Publications

In Preparation
Persad, Geeta, Xiaochun Zhang, and Ken Caldeira. “

Feedstock Vs. Fuel: Which Is The Less Carbon Intensive Use Of Domestic Natural Gas In The Transportation Sector?

”. Environmental Research Letters (In Preparation). 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). We here show using a lifecycle assessment that, in the current national mix of natural gas power generation, BEVs outperform CNGVs sourced from the same domestic natural gas across a range of metrics, including carbon dioxide emissions per kilometer driven and offsets from methane leakage. These results suggest that current governmental support for investment in compressed natural gas fueling infrastructure would not be carbon optimal compared to electric charging infrastructure in an economy in which domestic natural gas were the dominant fossil fuels. 
Persad, Geeta, Yi Ming, and V Ramaswamy. “

Spatially Similar Surface Heat Flux Responses To Present-Day Aerosols And Greenhouse Gases

”. Nature Geosciences (In Preparation). Print.Abstract
Recent studies suggest that present-day greenhouse gases and aerosols produce similar patterns of climate response in fully coupled general circulation model simulations, despite having significantly different spatial patterns of top-of-atmosphere forcing. Surface flux perturbations are a crucial pathway by which atmospheric forcing is communicated to the ocean, and may be a vital link in explaining the spatial similarities in the fully coupled responses to disparate forcing patterns—a phenomenon with implications for detection and attribution, as well as the climate sensitivity to different forcers. We here analyze the surface energy budget response to present-day aerosols versus greenhouse gases in fixed sea surface temperature, atmospheric general circulation model simulations to identify surface flux perturbation mechanisms for response pattern formation. We find that, although the top-of-atmosphere forcing spatial patterns of greenhouse gases and aerosols are largely uncorrelated, their surface radiative and heat flux patterns are significantly anti-correlated. This anti-correlation is largely explained by similar, but sign-reversed, spatial patterns of surface latent and sensible heat flux responses to the two forcers, particularly over the winter-hemisphere extratropical oceans. These are driven by spatially similar perturbations in surface winds from changes in mean tropical and mid-latitude circulation. These results suggest that the mean atmospheric circulation, which has many anti-symmetric responses to greenhouse gases and aerosols, is an efficient homogenizer of spatial patterns in the surface heat flux response to heterogeneous top-of-atmosphere forcings, creating an atmosphere-only pathway for similarities in the fully coupled response.
2012
Persad, GG, Y Ming, and V Ramaswamy. “

Tropical Troposphere-Only Responses To Absorbing Aerosols.

”. Journal Of Climate 25 (2012): 2471-2480. Web. Publisher's Version jcli-d-11-00122%2E1.pdf
2010
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
Two Opposing Effects.pdf