Earth system climate-carbon response to pulses and continuous negative emissions

Carbon Dioxide Removal (CDR) encompasses a wide range of anthropogenic activities to remove CO2 from the atmosphere to reduce its climate warming effect. The implementation of CDR technologies is necessary to achieve global climate-temperature goals. Commonly, negative emissions effects on the climate and carbon cycle have been thought to be nearly equal but opposite to those of positive emissions. This assumption was challenged recently, with results showing an asymmetric response of the Earth system to positive and negative emissions over a 1000-year timescale (Zickfeld et al. 2021). Positive emissions showed a more potent effect at increasing atmospheric CO2 concentration than negative emissions at reducing it. Yet, positive emissions had a less potent effect at increasing atmospheric temperature than negative emissions at decreasing it. Here we aim to re-evaluate the asymmetric climate-carbon response of the Earth system to negative emissions in a shorter-immediate timescale using an emissions-driven approach. Starting from a preindustrial spin-up the University of Victoria Earth system climate model (version 2.10) was forced with 10 PgC/yr emitted to the atmosphere until the cumulative carbon emission budget reached 1000 PgC (esmflat-10-1000PgC). Thereafter, pulses of positive and negative CO2 emissions ranging from ±50 to ±750 PgC were emitted or removed instantly. To assess the transient climate response to cumulative negative CO2 emissions a -10 PgC/yr was carried. Finally, a zero  emission simulation from pre-industrial served as a control. Our results show agreement with the temperature and carbon asymmetry shown in previous studies. However, we only observed relative large differences with regards to atmospheric temperature and carbon redistribution in the first 40 years of simulations. Later responses (>50 years) show much small differences between the mirrored atmospheric CO2 concentrations and temperatures to negative and positive emissions. The transient climate response to cumulative CO2 emissions and cumulative CO2 removal was found to be 1.81 and -1.79 K/EgC, respectively. These findings suggest that, while temperature asymmetry may remain undetectable in the first century of negative emissions deployment, carbon cycle dynamics could deviate significantly from symmetric assumptions. This highlights the importance of accounting for asymmetric carbon redistribution when designing negative emission strategies.

 

References:
Zickfeld, K., Azevedo, D., Mathesius, S. et al. Asymmetry in the climate–carbon cycle response to positive and negative CO2 emissions. Nat. Clim. Chang. 11, 613–617 (2021). https://doi.org/10.1038/s41558-021-01061-2