Dear All, Here is the link to our recent paper on the efficacy of Methane in Climate Dynamics.
https://link.springer.com/article/10.1007/s00382-018-4102-x?wt_mc=Internal.Event.1.SEM.ArticleAuthorOnlineFirst The efficacy of methane is probably not directly linked to geoengineering but is an important component of climate change discussions as Methane is one of the most important short-lived climate forcers. Does shortwave absorption by methane influence its effectiveness? - Angshuman Modak <angshu...@iisc.ac.in> - Govindasamy Bala - Ken Caldeira - Long Cao Abstract In this study, using idealized step-forcing simulations, we examine the effective radiative forcing of CH4 relative to that of CO2 and compare the effects of CH4 and CO2 forcing on the climate system. A tenfold increase in CH4 concentration in the NCAR CAM5 climate model produces similar long term global mean surface warming (~ 1.7 K) as a one-third increase in CO2 concentration. However, the radiative forcing estimated for CO2 using the prescribed-SST method is ~ 81% that of CH4, indicating that the efficacy of CH4 forcing is ~ 0.81. This estimate is nearly unchanged when the CO2 physiological effect is included in our simulations. Further, for the same long-term global mean surface warming, we simulate a smaller precipitation increase in the CH4 case compared to the CO2 case. This is because of the fast adjustment processes—precipitation reduction in the CH4 case is larger than that of the CO2 case. This is associated with a relatively more stable atmosphere and larger atmospheric radiative forcing in the CH4 case which occurs because of near-infrared absorption by CH4 in the upper troposphere and lower stratosphere. Within a month after an increase in CH4, this shortwave heating results in a temperature increase of ~ 0.8 K in the lower stratosphere and upper troposphere. In contrast, within a month after a CO2 increase, longwave cooling results in a temperature decrease of ~ 3 K in the stratosphere and a small change in the upper troposphere. These fast adjustments in the lower stratospheric and upper tropospheric temperature, along with the adjustments in clouds in the troposphere, influence the effective radiative forcing and the fast precipitation response. These differences in fast climate adjustments also produce differences in the climate states from which the slow response begins to evolve and hence they are likely associated with differing feedbacks. We also find that the tropics and subtropics are relatively warmer in the CH4 case for the same global mean surface warming because of a larger longwave clear-sky and shortwave cloud forcing over these regions in the CH4 case. Further investigation using a multi-model intercomparison framework would permit an assessment of the robustness of our results. -- With Best Wishes, ------------------------------------------------------------------- G. Bala Professor Center for Atmospheric and Oceanic Sciences Indian Institute of Science Bangalore - 560 012 India Tel: +91 80 2293 3428; +91 80 2293 2505 Fax: +91 80 2360 0865; +91 80 2293 3425 Email: gb...@caos.iisc.ernet.in; bala....@gmail.com Web:http://caos.iisc.ernet.in/faculty/gbala/gbala.html ------------------------------------------------------------------- -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to geoengineering+unsubscr...@googlegroups.com. To post to this group, send email to geoengineering@googlegroups.com. Visit this group at https://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/d/optout.
