Negative CO2 emissions for long-term mitigation of extremes in land hydrological cycle

Global warming has profound effects on the terrestrial hydrological cycle, leading to alterations in regional extreme weather patterns. While terrestrial precipitation responses under continued greenhouse gas emissions are well established, the responses of terrestrial precipitation and vegetation feedbacks under climate mitigation scenarios remain uncertain. Here, we investigate terrestrial precipitation changes under idealized negative and zero CO₂ emissions scenarios using the Community Earth System Model version 2 (CESM2). Terrestrial precipitation increases by approximately 1.1% at the peak CO₂ concentration ( ~ 725 ppm), but shows even greater increases of about 1.9% and 2.5% under substantially lower atmospheric CO₂ concentrations following zero ( ~ 600 ppm) and negative ( ~ 430 ppm) CO₂ emissions, respectively. Our results suggest that enhanced transpiration from terrestrial vegetation largely contributes to this increase under the negative emissions scenario. Furthermore, despite a substantial increase in terrestrial precipitation, extreme precipitation events and droughts become less severe globally under the negative emissions scenario, even compared to the zero emissions scenario. While near-term mitigation is essential to curb immediate warming, these findings suggest that sustained negative emissions could be effective for achieving long-term reductions in hydrological extremes and enhancing terrestrial water availability.