His idea isn’t to nuke the planet itself, but to use nuclear fusion to emit a series of explosions in the atmosphere in the polar regions. The aim is to melt the ice caps to produce carbon dioxide. The absence of polar ice would decrease the planet’s albedo, which would warm it. The carbon dioxide in the atmosphere would act as a greenhouse gas, and also warm the atmosphere. Maybe this would make the planet warm enough for human habitation? Also, perhaps we could use some of the said CO2 to make oxygen so people could breathe there?