The IPCC did a lot of detailed work, in fact a surprising amount considering the lack of contributors who had actually published anything in peer-review literature before. A lot of this was to support the central ideas required to convince people of climate change. Since Carbon dioxide does not actually absorb much energy that has previously escaped absorption by water or existing carbon dioxide levels, it was important to deal with other greenhouse gases.
One of the powerful greenhouse gases associated with human activity is methane, biogenic methane being produced by farming among other sources. Of course anyone modelling future climate would need to estimate the levels of methane, so how were the predictions now we can predict them against actual changes seen in the atmosphere?
Well I’m convinced that the IPCC could avoid arse/elbow confusion, although some are not.
Thanks again to those Small, Dead Animals.