CH4 —
yes, the rate at which, as a
feedback, a C reservoir is depleted with some fraction going into the atmosphere would be relatively more impotant if more of it is as CH4; if Chuvian runaway (thanks, wili) can be achieved, to the point of exhausting some (designated portion of a) surface C reservoir, with a CH4 flux, then there would be a cooling period afterword (setting aside other
slow feedbacks), and if the CH4
feedback were
slowed down, then the
feedback wouldn't be as strong, and perhaps the C reservoir wouldn't be exhausted unless the external forcing were larger (this being a hypothetical discussion; no assertion that it will happen).