Closing in on Zero Emissions Commitment (ZEC) uncertainty

Abstract

A stabilisation of global temperature can be achieved by reducing anthropogenic CO2 emissions to zero. Delayed warming or cooling, called zero emissions commitment (ZEC), can still occur after emissions have stopped. The magnitude of ZEC has been estimated to be 0±0.3 degrees Celsius, based on multi-model means. The individual models, however, show a wide range of responses from the climate system to the cessation of emissions, furthering the uncertainties regarding future temperature developments. Therefore, it is crucial to improve our knowledge of the ZEC uncertainty range in multiple aspects. This study contributes to a better understanding of the leading drivers of uncertainty of ZEC by analyzing a perturbed parameter ensemble of key dynamics of ZEC in ambitious mitigation scenarios. Using an Earth system model of intermediate complexity (UVic ESCM), we quantify how model parameters affect ZEC estimates for zero emissions preceded either by idealised constant emissions (20 and 10 PgC/yr) or by net-negative emissions scenarios. Finally, we analyze how the efficiency of Earth system processes relevant to ZEC, like carbon burial and heat uptake, can vary over different timescales after cessation of emissions.