As we count down to the 4th International Conference on Carbon Dioxide Removal in Milano, we are hosting a series of discussions on the research that will be shaping our sessions this June.
This study examines whether regional climate extremes are truly reversible after a temperature overshoot. By identifying “vulnerability hotspots,” the researchers show that the timing and specific type of CDR deployment, especially land-based methods, significantly modulate local heat risks beyond what global mean temperature averages suggest.
Full Abstract: Overshoot vulnerability hotspots: regional heat extremes and land–atmosphere feedbacks under plausible CDR portfolio pathways
Shraddha Gupta, Ronan McAdam, Daniele Peano, Barbara Cardeli, Matteo Mastropierro, Tomas Lovato, Julia Pongratz
There is an increasing dependence on carbon dioxide removal (CDR) strategies in mitigation pathways aiming at net-zero and net-negative emissions, which often allow for a temporary exceedance of temperature targets before cooling is achieved. While global mean temperatures may eventually be restored, it remains unclear whether regional climate extremes and underlying land–atmosphere feedbacks respond reversibly to such temperature overshoot. Understanding these responses is critical, as extreme heat strongly affects ecosystems, human health, and socio-economic resilience, and may not scale uniquely with global mean temperature across scenarios.
Here, we assess how realistic CDR portfolio pathways influence regional heat extremes and land–atmosphere interactions, and identify “overshoot vulnerability hotspots” where transient warming leads to amplified or persistent climate risks. The analysis is based on emission-driven simulations with fully interactive Earth System Models with explicit representation of multiple CDR methods, including afforestation/reforestation, bioenergy with carbon capture and storage, direct air carbon capture and sequestration, and ocean alkalinity enhancement, conducted within the RESCUE project. The multi-model scenario ensemble includes paired overshoot and non-overshoot pathways applying the full CDR portfolio, with identical carbon budgets and global temperature targets, differing in the timing and magnitude of CDR deployment.
We analyze regional heat extremes and compound hot–dry events in relation to large-scale circulations, surface energy partitioning, and evaporative cooling diagnostics. Responses are compared across overshoot and non-overshoot pathways at identical global mean temperature levels, and between warming and cooling phases in overshoot scenarios, to assess path dependence and reversibility. Results show that regional heat extremes at a given warming level differ systematically between overshoot and non-overshoot pathways, demonstrating path dependence of extremes even when global mean temperatures are identical. Comparison with the baseline no-CDR scenario reveals that land-based components of the CDR portfolio, such as afforestation, locally dampen extreme heat through enhanced evaporative cooling, demonstrating that the type and timing of CDR deployment modulate regional climate extremes beyond what is implied by temperature overshoot alone.
By explicitly linking CDR-driven overshoot to regional heat extremes, land–atmosphere feedbacks, and their reversibility, this work advances the understanding of how regional extremes are affected by specific CDR portfolios, to identify potentially preferable portfolios with respect to mitigated extremes. Identifying overshoot vulnerability hotspots provides a process-based framework for evaluating risks, informing adaptation needs, and supporting near-term decision-making on CDR deployment strategies and their integration with broader mitigation efforts.
If regional climate extremes are “path-dependent”, meaning they don’t simply reset once we lower global temperatures, should we be more cautious about “overshoot” pathways that rely on future CDR to clean up today’s emissions?