Pollution is now implemented. How it works is that a planet stores barrels of toxic waste from current output for the next turn. The environment slider cleans up the last turn's pollution. So on the first turn, you don't have pollution to clean up, but after that you will have to start cleaning up.
The more output you generates, the more pollution you generate as well. So for example, if you research a technology that doubles your construction output, it will also double your construction pollution. This will not be the same as MoO 1's pollution where eventually pollution goes away. Pollution will be a constant thorn in your side the entire game.
What if you decide to ignore pollution and hope it just goes away? Well, if you're on a terran planet, and you reach 1,000 barrels, it degrades into one of the two planet types, depending on if it's a wet climate or not, Jungle or Steppe. If you still ignore the pollution, and it reaches 2,000, it changes to Ocean or Desert. And so forth, with the threshold doubling each level. Finally if you're STILL polluting on a radiated planet, it will be destroyed and become asteroids, at which point your people are wiped out on that planet, unless you're a space race that don't care.
This is the tweaked planet UI. This was originally Terran, but I've polluted it to 4k, causing it to become Desert.
You can clean up pollution, but you cannot change the planet back without terraforming. So you gotta watch your pollution! However, on less desirable planets, the threshold is very high (for radiated, it's 128,000 barrels).
There will be random events that add a large amount of pollution and damage your precious planets. *Evil laughter*