I always have coastal cities and their production lines are far too important, to disrupt with a build order for domes. When sea levels rise (and to be fair, I'm usually the most to blame for it), there's always a planetary council call to launch a solar shade. I don't always get my way, but those who oppose me on the issue will the dominated ASAP if I can, so that we can re-vote on the issue at the next opportunity.
I'm not saying Earth's current factions are wrong simply because they don't play like me, but... it sure looks dumb. And as is typical, those who you'd think have the most to lose (or at least should think they have the most to lose) are the ones most responsible for the problem and best equipped to do something about it.
I know what you're thinking: it's zero sum. Sure, the developed countries will lose many cities, but so will their opponents. (Earth example: US might lose New York but Nigeria will lose Lagos, and Nigeria is poor so their loss of Lagos will hurt more, ergo, US wins by this disaster.) I would point out, though, that the more advanced factions will have a greater investment in their cities. Also, if you know what you're doing, your HQ will be coastal (always put your HQ on a coast) so that you can send sea crawlers to ocean hotspots. Winning a large map game is always about energy, in the end, because more energy means more tech, and more tech means both 1) better weapons and 2) first shot at the best Secret Projects. And hey, your coastal HQ probably has some mighty fine Secret Projects in it. Those are irreplaceable. This isn't the kind of situation where zero sum thinking is wise.