Does the game discuss what's happening back on Earth whiel you're around another planet?
You can build a Warp Gate later on, depending on your victory path.
I haven't gotten that far yet, so I don't know if there's any interaction fleshed out. Hopefully, but I'm not really expecting it.
Great game so far, very enjoyable.
Logically, a nuclear conflict would result in a global cooling from ash in the atmosphere rather than a global warming. The only explanation I can think of is that there was a geoengineering attempt to repair the damage from the nuclear war, which backfired.
But the cooling effect would be temporary: it would only take a few years (at absolute worse) for the ash to finish clearing from the atmosphere. Climate change, on the other hand, is based on a mix of factors which all take much longer to flush out of the atmosphere and has all sorts of positive feedback loops which can occur. There could have been a number of unstoppable feedback loops which had kicked in by the time the nuclear exchanges started.