Dr Drew Shindell (B.A., 1988, University of California Berkeley, Ph.D., 1995, State University of New York at Stony Brook) according to Wikipedia is “is an ozone specialist and climatologist at the NASA Goddard Institute for Space Studies. His research is concerned with global climate change, climate variability, and atmospheric chemistry. He uses climate models to investigate chemical changes such as the depletion of the ozone layer, climate changes such as global warming, and the connections between these two” (see: http://en.wikipedia.org/wiki/Drew_Shindell and http://www.giss.nasa.gov/staff/dshindell.html ).
Dr Drew Shindell and colleagues (NASA's Goddard Institute for Space Studies) have published a paper in the prestigious scientific journal Science (US) that takes gas-aerosol interactions into account in assessing the GWP effectiveness of various GHGs as summarized in the Abstract of their paper : “Evaluating multicomponent climate change mitigation strategies requires knowledge of the diverse direct and indirect effects of emissions. Methane, ozone, and aerosols are linked through atmospheric chemistry so that emissions of a single pollutant can affect several species. We calculated atmospheric composition changes, historical radiative forcing, and forcing per unit of emission due to aerosol and tropospheric ozone precursor emissions in a coupled composition-climate model. We found that gas-aerosol interactions substantially alter the relative importance of the various emissions. In particular, methane emissions have a larger impact than that used in current carbon-trading schemes or in the Kyoto Protocol. Thus, assessments of multigas mitigation policies, as well as any separate efforts to mitigate warming from short-lived pollutants, should include gas-aerosol interactions.” [1].
The key technical quote from Shindell et al. (2009) provides an estimate that the GWP of CH4 relative to CO2 on a 20 year time scale is 79 (without aerosol effects) and 105 (with aerosol effects considered): “Fig.2. The 100-year GWPs for methane, CO, and NO x (per Tg N) as given in the [IPCC] AR4 and in this study when including no aerosol response, the direct radiative effect of aerosol responses, and the direct+indirect radiative effects of aerosol responses. The AR4 did not report uncertainties for methane or CO and gave no mean estimate for NO x . The range for the GWP of CO is from the third IPCC assessment and encompasses values reported up through the AR4. Our calculations for the shorter 20-year GWP, including aerosol responses, yield values of 79 and 105 for methane, 11 and 19 for CO, and –335 and –560 for NO x , including direct and direct+indirect radiative effects of aerosols in each case. The 100-yr GWPs for SO 2 (per Tg SO 2 ) and ammonia would be –22 and –19, respectively, including direct aerosol radiative effects only, and –76 and –15 adding indirect aerosol radiative effects. GWPs for very short-lived NO x , SO 2 , and ammonia will vary widely by emission location and timing, and hence global values are of limited use.” [1, 2].
Dr Drew Shindell (NASA Goddard Space Institute), Robert Howarth (41-Nobel-Laureate Cornell University), Renee Santoro (41-Nobel-Laureate Cornell University), Anthony Ingraffea (41-Nobel-Laureate Cornell University), Nathan Phillips (7-Nobel-Laureate Boston University) and Amy Townsend-Small (University of Cincinatti), “Methane emissions from natural gas systems” (a background paper prepared for the National Climate Assessment): “Methane [the major component of natural gas] is the second largest contributor to human-caused global warming after carbon dioxide … For the 20-year time frame, Shindell et al. (2009) provide a mean estimate of 105 for the global warming potential . Using this value , Howarth et al. (21012) calculated that methane contributes 44% of the entire GHG inventory of the U.S., including carbon dioxide and all other gases from all human activities. Hence, while methane is only causing about 1/5 of the century –scale warming due to U.S. emissions, it is responsible for nearly half of the warming impact of current U.S. emissions over the next 20 years. At this time scale, the methane emissions from natural gas systems contribute 17% of the entire GHG inventory of the U.S,, for all gases from all sources, We repeat that these estimates may be low, and that the gradual replacement of conventional natural gas by shale gas is predicted too increase these methane fluxes by 40% to 60% or more (Howarth et al, 2012)”. [3].
[1]. Drew T. Shindell , Greg Faluvegi, Dorothy M. Koch , Gavin A. Schmidt , Nadine Unger and Susanne E. Bauer , “Improved Attribution of Climate Forcing to Emissions”, Science, 30 October 2009:
Vol. 326 no. 5953 pp. 716-718: http://www.sciencemag.org/content/326/5953/716 .
[2]. 27 Shindell et al (2009), Fig.2: http://www.sciencemag.org/content/326/5953/716.figures-only .
[3]. Robert Howarth, Dr Drew Shindell, Renee Santoro, Anthony Ingraffea, Nathan Phillips, and Amy Townsend-Small, “Methane emissions from natural gas systems” (a background paper prepared for the National Climate Assessment, reference number 2011- 0003; February25 2012: http://www.eeb.cornell.edu/howarth/Howarth%20et%20al.%20--%20National%20Climate%20Assessment.pdf ).