I did a test run, by observin bots, and it seems things... dont work exactly as expected. I generated map with 20k tiles, and created 25 pouluted tiles, at first polution rate was positive, and chance for global warming rose, rose and then it hit like a ton of bricks, chaning lots of terrain. Then it reset to 0, and sadly pollution rate also reset to 0, so I had to add more polution. This means there needs to be a patch with option ether for ruleset or server option for constant/base global warming/nuclear winter chance. Though I'd guess its doable.
As for adding terrains - freeciv currently has it that terrain can change only into two different things, when warming (and two more for cooling) depending on wetness of surroundings. This is not good/not realistic for melting of ice age scenario, as all the glaciers would reveal tundra, which when would become desert, well on the shores it would be a bit different, but thats it, nether forrests nor mountains nor hill would ever appear from under glacier. Thus you clone galcier, change warming result for this copy, adjust it's wetness, greenness, mountainess according to result, so that generator would generate something, what would look like normaly generated map after defrost (though not exactly) though how much "normaly" it would look would very much depend. But anyways the point is that there needs to be more variaty what happens when warming(cooling) hits. Since by default rules are to basically create bad stuff on warmin, as in to discourage pollution.
Another thing I norice is that rulesets can have lua scripts! havent looked much at them, will have to lookup documentation and if does not exit possibly source to see what can be done, maybe one could simply trigger warming from lua script on certain turns. It also very interesing what does lua scripting allow overall, it might be that it can allow some crazy awesome stuff!
Edit: I see you got the reason. But no, you can
choose identical display names!
only data values have to be different. Ofc if someone wants he probably can hack client to extract them, but maybe people wont do that