After 'Net Zero': Tracing uncertainties in the Zero Emissions Commitment signal

One of the defining challenges of our century is to limit global warming. Reducing anthropogenic carbon dioxide emissions to net zero has been understood to be a central measure in achieving this climate goal. Still, after achieving net zero CO₂ emissions, the climate system could show a delayed temperature response. This temperature response is called Zero Emissions Commitment (ZEC) and has been estimated to be approximately 0±0.3 K in the ZECMIP multi-model mean (Jones et al., 2019; MacDougall et al., 2020). Understanding and constraining ZEC remains relevant, especially when considering the remaining carbon budget for reaching ambitious climate targets. However, individual climate models show a high level of uncertainty in the ZEC response.

ZEC is closely related to the carbon cycle, the planetary heat uptake and their respective distance to their equilibrium states at the point of net zero. Therefore, we investigate how the pre-industrial state and responsiveness of these processes to anthropogenic climate change relate to their ZEC response in Earth system models simulating the ZECMIP experiments. We aim to characterise the models' ZEC response as a function of the chosen, observable climate variables (e.g., overturning strength at 26° N, global carbon project (Friedlingstein et al., 2023) carbon fluxes, or ocean heat content of the upper 700 m), that will then later serve as basis for observationally constrained ZEC estimates. We will show first preliminary results and invite feedback on the study design.

 

References

Friedlingstein, P. et al. (2023). “Global Carbon Budget 2023” Earth System Science Data 15 (12): 5301–69. https://doi.org/10.5194/essd-15-5301-2023.

Jones, C.D. et al. (2019). “The Zero Emissions Commitment Model Intercomparison Project (ZECMIP) Contribution to C4MIP: Quantifying Committed Climate Changes Following Zero Carbon Emissions” Geoscientific Model Development 12 (10): 4375–85. https://doi.org/10.5194/gmd-12-4375-2019.

MacDougall, A.H. et al. (2020). “Is There Warming in the Pipeline? A Multi-Model Analysis of the Zero Emissions Commitment from CO₂” Biogeosciences 17 (11): 2987–3016. https://doi.org/10.5194/bg-17-2987-2020.