Asymmetric carbon-climate responses to cumulative emissions under different CO2 pathways

While previous research has extensively explored the effects of rising CO2 levels, the response of the climate and carbon cycle to reductions in CO2 remains less understood. In this study, we are going to uncover the asymmetric carbon-climate responses and underlying processes under different emission pathways, including decreasing and negative CO2 emissions.Based on the Max Planck Institute Earth System Model (MPI-ESM1-2-LR), we have run a large ensemble of simulations incorporating an interactive carbon cycle under different future scenarios to quantify variations in atmospheric CO2 growth, along with carbon sinks in response to changing emissions. We found asynchronous changes in the atmospheric CO2 and emissions driven by carbon sinks, and the ocean and land become CO2 sources after ~2100 under negative emissions. While the climate responses to cumulative emissions along increasing pathways overlap, the responses along decreasing pathways are asymmetric and show uncertainties in the presence of internal climate variability.Further idealized flat10 simulations with constant positive and negative CO2 emissions allow us to quantify the response of the carbon sink and climate under deep decarbonization. The climate and carbon cycle is irreversible even under the accumulation of zero emissions, featuring a lower global temperature and atmospheric CO2 concentration. An asymmetric response in the carbon uptake and release, and the ocean storage of carbon and heat intervene in the transient responses of climate to the cumulative CO2 emissions.By leveraging these simulations under diverse scenarios, we seek to enhance our understanding of the transient climate response, providing insights into the potential impacts of emission reduction strategies and the role of negative emissions in climate mitigation.