Ambitious Co-scaling of Carbon Dioxide Removal and Decarbonization Delivers Better Climate Outcomes Than Strategies That Prioritize Efforts in One Domain.

Concerns about mitigation deterrence have prompted calls for pathways that avoid multigigatonne reliance on carbon dioxide removal (CDR), yet such pathways can also discourage near-term investment in CDR, leaving the technologies technically and economically underprepared if large-scale deployment becomes necessary due to unfulfilled emission reduction pledges. Here we model a new pathway in which CDR and decarbonization "Co-Scale" aggressively in parallel without one undermining the other, with the intention that we can readily course-correct if effort in one domain does not materialize. We treat this scenario as a stylized upper bound of what is climatically achievable under ideal enabling conditions, rather than what is immediately feasible under current technical, economic, and environmental constraints. We compare this pathway with two conventional designs, i.e., CDR-Led and Decarb-Led. In CDR-Led, large-scale CDR can substitute for deep decarbonization, while in Decarb-Led, rapid emissions reductions are prioritized and CDR plays a limited complementary role. We find that compared to these two conventional scenarios, Co-Scale reaches net zero CO2 seven years earlier, accumulates 4 times more net negative CO2 by 2100, cuts the 1.5 °C overshoot duration by roughly half, and limits end-of-century warming to 1 °C rather than 1.37-1.39 °C. Relative to the recent focus on Decarb-Led pathways, Co-Scale's main constraints is the feasibility of geological carbon storage, while food, water, and cost pressures are comparatively less restrictive.