|2011-07-29 20:33:12||Large methane releases lead to strong aerosol forcing and reduced cloudiness|
Yooper & Agnostic - this seems to be your kettle of fish, ran across it while researching:
"The release of vast quantities of methane into the atmosphere as a result of clathrate destabilization is a potential mechanism for rapid ampliﬁcation of global warming. Previous studies have calculated the enhanced warming based mainly on the radiative eﬀect of the methane itself, with smaller contributions from the associated carbon dioxide or ozone increases. Here, we study the eﬀect of strongly elevated methane (CH4) levels on oxidant and aerosol particle concentrations using a combination of chemistrytransport and general circulation models. A 10-fold increase in methane concentrations is predicted to signiﬁcantly decrease hydroxyl radical (OH) concentrations, while moderately increasing ozone (O3). These changes lead to a 70% increase in the atmospheric lifetime of methane, and an 18% decrease in global mean cloud droplet number concentrations (CDNC). The CDNC change causes a radiative forcing that is comparable in magnitude to the longwave radiative forcing (“enhanced greenhouse eﬀect”) of the added methane. Together, the indirect CH4 -O3 and CH4 -OH-aerosol forcings could more than double the warming eﬀect of large methane increases. Our ﬁndings may help explain the anomalously large temperature changes associated with historic methane releases"
There was another similar study published few months ago which identified some other mechanisms for these kinds of methane feedbacks. Also, I have been in contact with the lead author (he's in a Finnish Google group that I'm member of) in case there's a need to contact him.