Comprehensive evidence implies a higher social cost of CO2

<jats:title>Abstract</jats:title><jats:p>The social cost of carbon dioxide (SC-CO<jats:sub>2</jats:sub>) measures the monetized value of the damages to society caused by an incremental metric tonne of CO<jats:sub>2</jats:sub> emissions and is a key metric informing climate policy. Used by governments and other decision-makers in benefit–cost analysis for over a decade, SC-CO<jats:sub>2</jats:sub> estimates draw on climate science, economics, demography and other disciplines. However, a 2017 report by the US National Academies of Sciences, Engineering, and Medicine<jats:sup>1</jats:sup> (NASEM) highlighted that current SC-CO<jats:sub>2</jats:sub> estimates no longer reflect the latest research. The report provided a series of recommendations for improving the scientific basis, transparency and uncertainty characterization of SC-CO<jats:sub>2</jats:sub> estimates. Here we show that improved probabilistic socioeconomic projections, climate models, damage functions, and discounting methods that collectively reflect theoretically consistent valuation of risk, substantially increase estimates of the SC-CO<jats:sub>2</jats:sub>. Our preferred mean SC-CO<jats:sub>2</jats:sub> estimate is $185 per tonne of CO<jats:sub>2</jats:sub> ($44–$413 per tCO<jats:sub>2</jats:sub>: 5%–95% range, 2020 US dollars) at a near-term risk-free discount rate of 2%, a value 3.6 times higher than the US government’s current value of $51 per tCO<jats:sub>2</jats:sub>. Our estimates incorporate updated scientific understanding throughout all components of SC-CO<jats:sub>2</jats:sub> estimation in the new open-source Greenhouse Gas Impact Value Estimator (GIVE) model, in a manner fully responsive to the near-term NASEM recommendations. Our higher SC-CO<jats:sub>2</jats:sub> values, compared with estimates currently used in policy evaluation, substantially increase the estimated benefits of greenhouse gas mitigation and thereby increase the expected net benefits of more stringent climate policies.</jats:p>