We have a paper (with Frank Errickson, Klaus Keller, William Collins, and David Anthoff published today in Nature on the social cost of methane (SC-CH4). The social cost of a greenhouse gas quantifies the net present value of emitting a unit amount of the gas (in this case, methane) into the atmosphere. This cost enables cost-benefit analyses of regulations proposing changes to limits on their emissions, which are a required part of the regulatory process.

We show how several factors influence estimates of the SC-CH4, including how:

  • accounting for climate-system uncertainty by calibrating a climate model to historical observations results in a decreased estimate compared to that used by the US government, partially due to nonlinear relationships between uncertainties related to temperature dynamics;
  • the sensitivity of SC-CH4 to scenarios of future warming is of a comparable magnitude to that resulting from different discount rates;
  • the SC-CH4 estimates vary little when different climate models are used, but show large sensitivities to the choice of damage function (which is usually the most contentious part of any monetized climate impacts analysis); and
  • the use of equity-weighting instead of constant discount rates results in large increases in the SC-CH4 for wealthier regions such as the US compared to regions which consume less, justifying higher mitigation expenditures in high-income countries, and these increases dwarf the decreases from climate uncertainties.

The paper is not open access, but the News and Views perspective is available here.