DISCLAIMER: I'm neither developer, nor modder, this is the way I solved the problem, it might not work for you, the way save files work might change in future, this guide is written for version 1.4


The issue I had is:

"I got hit by multiple purple events in a row (Long Night, Ice Age, Psychic Rain and Global Warming), about 15 days between them. The problem was probably caused exclusively by Ice Age and Global Warming overlapping though.

Ice Age was still active when Global warming was rolled. The biome of the colony changed from temperate forest to boreal forest with Ice Age (probably, could misremember this part), then from boreal back to temperate with Global Warming. It stayed temperate when Ice Age ended. When Global Warming ended it went to boreal.

Now (without any events active) the biome is boreal forest instead of temperate forest, which it was originally (the temperatures and growing periods are also affected everywhere (including modded biomes that don't change due to these events))."

If you have any similar problem, it is possible to restore original biomes using save editing.


The steps are:

1. Open the save file of your colony in any text editor that can handle it (see Rimworld Wiki[rimworldwiki.com]).

2. Find section <world> (the easiest way is to search (Ctrl + f) for <world>).

3. In <info> subsection take a look at the <seedString>, <planetCoverage>, <overallRainfall> and <overallTemperature>.

4. Now launch the game and start a new game with these four world settings being identical, everything else doesn't matter.

5. Save the new game, exit to menu and open it's save file, find <world> section there.

If you did everything correctly and there are no effects of Ice Age and Global Warming in the original save, you should have an unaltered state of planet in your new save. The data that we need is located in section <grid>. It is heavily encoded and compressed, fortunately we don't have to deal with it.
The mod changes two things: biomes and temperatures/growing periods. The first one is easy: subsection <tileBiomeDeflate>. The second one I didn't bother finding myself, but it was mentioned in comments that it is <tileTemperatureDeflate>.

6. Replace either whole <grid> section in old game with the section from new game, or replace only <tileBiomeDeflate> and <tileTemperatureDeflate>. You might need some additional text files to make it easier for you: the amount of data is huge and even one missed character could break your save entirely, backups are recommended.

7. Save changes and load the game, check biomes and temperatures, revert if needed by replacing save file with a backup (or renaming .rws.old to .rws), try again.


Final thoughts:

The method could could destroy roads and rivers, and would not work correctly if the procedure of world generation changed in any way since the original save creation (new mods, new biomes etc). However, all settlements (faction bases, quests, camps etc) seem to be unaffected by the <grid> subsection.

If you want to recover your save from permanent Ice Age/Global Warming, I believe some sort of save editing is required. The mod changes the save file itself, it doesn't seem to record previous states. To fix this problem these events should be rewritten in a different way, or some unavoidable check added that prevents two events from overlapping.

Hopefully this guide was helpful. In case of any issues report them in comments for other people to see.