Normalizing the permafrost carbon feedback contribution to the Transient Climate Response to Cumulative Carbon Emissions and the Zero Emissions Commitment

Abstract. As permafrost thaws, the permafrost carbon feedback (PCF) can amplify the Transient Climate Response to Cumulative Carbon Emissions (TCRE) and the Zero Emissions Commitment (ZEC) by introducing additional greenhouse gases into the atmosphere. Using a basic permafrost carbon response model coupled to the simple climate model FaIR, we estimate this feedback's contribution to TCRE and ZEC100 (ZEC at 100 years after emission cessation) and find that it can substantially increase estimates of these climate metrics. TCRE is increased by 0.12 % per PgCeq °C−1 of PCF and is robust in scenarios with various emission rates. ZEC100's increase is emission-rate-dependent but is increased by 0.006 °C per PgCeq °C−1 of PCF for emission rates of 10 PgC yr−1 and is robust for varying emission rates when time-integrated warming is considered. Relating these climate metrics to permafrost carbon emissions allows the normalization of the PCF contribution to TCRE and ZEC by discounting its uncertainties.