Is this a bug, attack or act of nature?

My state has a medium sized island all to itself, with about eight cities on it, plus territory elsewhere on the map.

Around the year 2200, some of those island cities just disapeared, with no sign of them having been nuked. Some of the landmass also turned to water. At this point, I have been involved in a longish conflict, and have lots of pollution.

Has a new weapon been used on me or is there another explanation? No mods are involved ....

It's called global warming. When the world's pollution reaches a certain point, the oceans rise, most coastal cities get destroyed, and a lot of terrain changes to desert or dryer types than what they were.

That's all it was.

Eek!