Cecil Adams goes through the thought experiment of how an Evil Genius might melt Earth’s icecaps, discarding one idea after another until landing on this:
See how this grabs you. We come up with a process that traps energy in the atmosphere rather than letting it radiate away, perhaps involving an accumulation of gases such as carbon dioxide or methane that would be transparent to incoming solar radiation but a barrier to surface heat. Sort of a, you know, greenhouse effect.
The beauty of this scheme is that once the heat built up to a certain point, cascading events would take you the rest of the way. Melting ice would release additional carbon dioxide and methane trapped within, accelerating warming. Thawing permafrost would release still more CO2, and if the oceans got toasty enough you could end up with a major release of frozen methane on the seabed, a process thought to have caused the Great Permian Extinction.
The problem from a cinematic standpoint is that no one genius, however evil, could pull this stunt off. The only way to generate enough CO2 would be combustion on a staggering scale-you’d need to enlist the bulk of the earth’s population in a decades-long campaign to burn through a significant fraction of the planet’s organic materials. Even if the plan were technically feasible, nobody would buy it as a movie premise.
Everybody pitches in to melt ice caps? Come on, you think we’re all fools?