An ad hoc multi-disciplinary committee will be appointed to inform future revisions to estimates of the social cost of carbon (SCC) developed and used by the federal government. The committee will examine the merits and challenges of potential approaches for both a near-term limited update and longer-term comprehensive updates to ensure that the SCC estimates continue to reflect the best available science and methods. The study will be conducted in two phases and will result in two reports.

Phase 1. In phase 1, the committee will assess the technical merits and challenges of a narrowly focused update to the SCC estimates and make a recommendation on whether to conduct an update of the SCC estimates prior to recommendations related to a more comprehensive update based on its review of the science related to the topics covered in the second phase. Specifically, the committee will consider whether an update is warranted based on the following:

• Updating the probability distribution for the equilibrium climate sensitivity (ECS )to reflect the recent consensus statement in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), rather than the current calibration used in the SCC estimates, which were based on the most authoritative scientific consensus statement available at the time (the 2007 Fourth IPCC Assessment).
• Recalibrating the distributional forms for the ECS by methods other than the currently-used Roe and Baker (2007) distribution.
• Enhancing the qualitative characterization of uncertainties associated with the current SCC estimates in the short-term to increase the transparency associated with using these estimate in regulatory impact analyses. Noting that as part of a potential comprehensive update Part 2 of the charge requests information regarding the opportunity for a more comprehensive, and possibly more formal or quantitative, treatment of uncertainty.

The phase 1 report will be an interim letter report to be completed in 6 months.

Phase 2. In phase 2, which represents the bulk of the statement of task, the Committee will examine potential approaches, along with their relative merits and challenges, for a more comprehensive update to the SCC estimates to ensure the estimates continue to reflect the best available science. The Committee will be asked to consider issues related to:

• an assessment of the available science and how it would impact the choice of integrated assessment models and damage functions;
• climate science modeling assumptions;
• socio-economic and emissions scenarios;
• presentation of uncertainty; and
• discounting.

Within these areas, the Committee will make recommendations on potential approaches that warrant consideration in future updates of the SCC estimates, as well as research recommendations based on their review that would advance the science in areas that are particularly useful for estimating the SCC.