I'm not saying make the entire thing Ice Sheets, but why not some different types of planets for different types of difficulties and challenges.
For example Cold planets feature no deserts, generally everything is colder, boreal forests are rare and most of the planet is Tundra, most people would be wearing Parkas, too.
Hot Planets would feature more deserts and less oceans, and a huge chunk of the population would be wearing Dusters and light clothing.
Earthly Planets feature a wide array of all the biomes, just like we have today.
This would be awesome. Everytime I wanted to challenge myself by selecting ice sheet/desert, I go eh, no fair, other tribes got to be on comfortable temperate forest biome.
How is this that different from adjusting the temperature/rainfall slider? If you adjust the temperature, there are more deserts/tundra/ice sheets, and if you adjust the rainfall you get more deserts/tundras or more forests.