Constraining uncertainties of the Zero Emissions Commitment with a large ensemble of UVic 2.10 climate model simulations

Achieving global temperature stabilisation requires net-zero CO₂ emissions, a goal widely recognised within the scientific community. However, a critical and contested question remains: will the Earth's climate continue to warm due to thermal and biogeochemical inertia even after emissions cease? This phenomenon, known as Zero Emissions Commitment (ZEC), has been estimated to likely be 0.0 ºC with a multi-model spread of 0.3°C. Considering its magnitude, ZEC may represent a significant fraction of the remaining warming before the 1.5°C threshold is reached.

In an attempt to constrain uncertainties in ZEC estimates, this study presents findings from a large ensemble of simulations conducted using the University of Victoria Earth System Climate Model (UVic ESCM v2.10). The ensemble design systematically varies model parameters within observationally constrained ranges, targeting processes identified as having the largest potential influence on ZEC (Palazzo-Corner et al., 2023). These parameters include carbon cycle feedbacks, ocean heat uptake, and CO₂ fertilisation effects, which are represented with appropriate and acceptable levels of complexity within the UVic ESCM.

In line with the CMIP7 emissions-driven experimental design focus, we employ the esm-flat10-zec as well as esm-flat20-zec, which uses a constant emission rate of 10 PgC/yr and 20 PgC/yr, respectively (Sanderson et al., 2024), with varying cumulative emission budgets. This approach allows for the exploration of ZEC parameter uncertainty under varying emission rates and carbon budgets, increasing our process-based understanding of the metric.

 

References

Sanderson, B. M. et al. The need for carbon-emissions-driven climate projections in CMIP7. Geoscientific Model Development 17, 8141–8172 (2024).

Palazzo Corner, S. et al. The Zero Emissions Commitment and climate stabilization. Frontiers in Science 1, 1170744 (2023).