In this interview, climate scientist Tom Wigley says that waiting to take significant action on climate change makes it more likely that geoengineering will be needed to address the problem. He advocates for research on a combination approach: climate engineering together with mitigation efforts aimed at reducing greenhouse gas emissions. Wigley says that geoengineering may become necessary to stabilize global sea level rise, because sea level has much greater inertia than temperatures in the atmosphere. He argues that the climate problem cannot be solved with renewable energy alone, and that, without turning to geoengineering, consideration of the nuclear energy pathway—in particular, resuming the development of fast reactors—should be an essential component of attempts to address the climate crisis. Wigley claims that his colleagues in climate science are generally supportive of nuclear engineering and less fearful of it than they are of geoengineering.