Geoengineering involves intentionally modifying the environment on a massive scale and is typically proposed as a last resort to prevent catastrophic harms caused by climate change. Critics argue that there are powerful moral reasons against researching, let alone undertaking, geoengineering. Perhaps most notably, Stephen Gardiner argues that even if we are forced to choose between allowing a climate catastrophe or geoengineering—and geoengineering is the less harmful option—it could still be the case that we ought not to geoengineer. This essay argues for a conditional: if we are indeed forced to choose between catastrophic environmental harm and the less harmful option of geoengineering, then we ought to geoengineer.

Sufficientarians claim that what matters most is that people have enough. I develop and defend a revised sufficientarian conception of justice. I claim that it furnishes the best specification of a general humanitarian ideal of social justice: our main moral concern should be helping those who are badly off in absolute terms. Rival humanitarian views such as egalitarianism, prioritarianism and the difference principle face serious objections from which sufficientarianism is exempt. Moreover, a revised conception of sufficientarianism can meet the most prominent undefeated challenges to the view. I contend that prevailing versions of sufficientarianism have not satisfactorily defined the sufficiency threshold, and so I offer an original specification of the threshold. I also address perhaps the most common objection to sufficientarianism, namely that sufficientarian regimes will channel all of society's resources towards elevating people to the sufficiency threshold regardless of the gains foregone by those above the threshold.