Event Recap

Reducing temperatures in the next few centuries requires use of either carbon removal (CDR) or solar geoengineering (SRM) or both. Emissions cuts should be the overwhelming focus of current efforts but zeroing emissions just stops making the problem worse—it cannot reduce temperatures on policy-relevant timescales. CDR and SRM differ in many dimensions. Yet it can be helpful to consider them as alternative methods of achieving the same fixed amount of additional cooling at some future time to enable comparison of their physical and social impacts. A CDR facility—industrial or biological—achieves nothing the day it starts, but only cumulatively, year upon year. So, the earlier one demands the cooling, the faster one must build the removal industry, and the higher the social costs and environmental impacts per degree of cooling. David Keith presented preliminary results comparing air pollution mortality and land use disturbance from SRM and CDR. These quantitative comparisons suggest that—contrary to widespread assumptions—SRM may be a substantially less risky way to achieve a given amount of additional cooling than is CDR.