I created a pocket world with no oceans, 100 HFS layers (ended up not mattering), very high min elevations so that the entire map was bounded by mountains and they covered most of the map. And most importantly, this world had min and max temperatures of 1000 (the highest it could go in advanced gen).



The whole playable world ended up being a few scorching desert valleys and scorching rocky wastelands tucked between these vast scorching mountains.



I wanted to see how civilization could handle living in a hell-like environment, so I disabled all megabeasts and semimegabeasts except forgotten beasts (because you can't control forgotten beasts in advanced gen).



The first few worlds I tried were dominated by goblins. Apparently they don't melt and can survive extreme heat perfectly fine. They would expand and settle as usual as if nothing was strange, except that there were no other civilized creatures except kobolds, the humans and dwarves the goblins conquered were very few in number. To study the other races more closely I disabled clowns/goblins.



I noticed that kobolds always survived, but I think this is because they stay inside caves where it is cooler. Worldgen still had them stealing things, but I think the game processes that too abstractly to melt them on their thieving trips.



I eventually settled on a particular world...



The world ended up running all the way to year 10,000 (max possible). At the end there were 2 dwarves and a few hundred kobolds left in existence. The entire span of history was the "age of dwarves".



It turns out those two surviving dwarves were necromancers who each lived alone in camps out in the desert. They survived the heat in worldgen because they were necromancers I guess. When I loaded the world and went into it as a human outcast adventurer, it spawned me right in a camp. I had to use alt-move to move everywhere because of the heat. I saw a necromancer and he immediately started smoking. I fast traveled away for a bit (in other tests I found out you don't melt in fast travel), then when I stopped I too started melting, and I died.



Looking through legends, it turns out that dwarves had actually survived for a few hundred years (in this time the necromancers were gifted immortality). But all five dwarven civs had never expanded beyond their initial fortresses. They were each destroyed by forgotten beasts within a few hundred years.



I spawned another adventurer, this time in the other camp. I approached the smoking necromancer and killed him with my spear (he started melting as we were fighting anyway). This time I had put max points into "toughness" and it actually worked - made me able to withstand the heat for much longer. I traveled to some abandoned dwarf fortresses but they were all very small because they didn't have time to grow before forgotten beasts killed them. I didn't find any forgotten beasts, but I noticed that once inside I could move without using alt (careful movement), so it must have been much cooler underground, explaining how kobolds, dwarves, and goblins could survive. The walls outside around the entrances were "warm" stone. As I approached each abandoned 10,000 year old fortress, the items in the trade depot would burst into flames. I could sleep from fast travel and no bogeymen would come. After about 1.5 days this character also finally melted. Even max toughness or necromancer immortality isn't enough.



I then went into fortress mode and tried to get my dwarves to dig into the side of a hill so I could rebuild civilization. I knew if I could just get them underground they would live, but they all melted as soon as I unpaused the game.



Since there is no way to disable forgotten beasts in advanced parameters, I simply spawned a new world with way more civilizations. This time there were so many dwarf civs that they couldn't all get killed early on, and indeed they survived for 1,300 years until I stopped generation. At that point the dwarf population had grown to a few thousand. They had even settled some mountain halls and hillocks, and had created libraries, taverns, performance troupes, lots of books, etc. No necromancers in this world though.



Surprisingly, in both these worlds I found that desert and mountain land animals were still plentiful according to the exported data, although I never encountered any with adventurers. Presumably they would have melted if I had.



This new world also had a few lakes, so I went down in adventure mode again to investigate. This time I was able to choose dwarves and intelligent wilderness creatures as well as human outcasts. I decided to be a vulture man and spawned inside a nice cool fortress, which I wandered a little and talked to some dwarves. The place was thriving. Unfortunately I melted almost as soon as I stepped outside, even with max toughness and endurance.



So I embarked at the intersection of a desert, lake, and mountain. Once again, the dwarves couldn't even begin digging because they all started melting. All the grass on the mountain biome part of the map immediately burst into flame on the first game tick. Likewise, the lake immediately boiled into a cloud of steam. A steam wall emerged on the edge of the map where new water was trying to pour in. A few moments later everyone was dead. I tried a few more times, but it was impossible to start a fortress.



I then created an opposite type of world, same as before except with normal precipitation and -1000 temperature instead of +1000. The world ended up very similar, with a few dwarf and kobold civs thriving underground. As soon as my dwarf adventurer emerged from the fortress I encountered a group of dwarves outside dying of frostbite before my eyes. I fast traveled away before the same could happen to me, but there wasn't anything cool to do in this empty world so I stopped playing.



I also did a few ocean worlds but I never actually accepted any of them, just looked at the maps. Humans were the only ones that lived in those, on isolated islands. The game doesn't really work with that kind of thing because there is no boat travel as of now.



To test this stuff for yourself, just go into advanced parameters, set min elevation between 250 and 300 for mountain world and turn off ocean edges (forget exactly what this parameter is called), or alternatively do an ocean world with elevations between 0 and 100, and set min and max temperatures to absurd values.