I remember watching a documantary about how the Chinese built the Tibet Railway. They had one serious problem up on the tundra, and that was that the top inch or two of the ground would not remain frozen all year round, meaning it would compromise the structural integrity of the track. They solved this problem by using a couple of solutions, but the key one was to refridgerate the underlying rock by exploiting the evaporation/condensation cycle. I can't remember what liquid they used, but they would put tubes upright into the ground with a liquid trapped inside. It would settle in the bottom, and evaporate, rising to the top as a vapour, where it would condese, and settle at the bottom as a liquid. Ths cycle would transfer heat from the ground to the atmopshere, reducing the local ground temperature just enough to keep it frozen all year round.

Them Chinese are smart fuckers.