Including climate system feedbacks in calculations of the social cost of methane

TL;DR

This paper enhances the calculation of the social cost of methane by incorporating climate feedbacks on the methane cycle, resulting in a significantly higher estimate than previous models without feedbacks.

Contribution

It introduces climate system feedbacks into IAMs for more accurate social cost of methane estimates, addressing a gap in existing models.

Findings

Estimated social cost of methane is $1163/t-CH$_4$ with feedbacks.

Feedbacks increase the social cost estimate by 44%.

Highlights the importance of including climate feedbacks in IAMs.

Abstract

Integrated assessment models (IAMs) are valuable tools that consider the interactions between socioeconomic systems and the climate system. Decision-makers and policy analysts employ IAMs to calculate the marginalized monetary cost of climate damages resulting from an incremental emission of a greenhouse gas. Used within the context of regulating anthropogenic methane emissions, this metric is called the social cost of methane (SC-CH$_4$). Because several key IAMs used for social cost estimation contain a simplified model structure that prevents the endogenous modeling of non-CO$_2$ greenhouse gases, very few estimates of the SC-CH$_4$ exist. For this reason, IAMs should be updated to better represent methane cycle dynamics that are consistent with comprehensive Earth System Models. We include feedbacks of climate change on the methane cycle to estimate the SC-CH$_4$. Our expected value for the SC-CH$_4$ is \$1163/t-CH$_4$ under a constant 3.0% discount rate. This represents a 44% increase relative to a mean estimate without feedbacks on the methane cycle.