Wow. I can see a few other things to increase the scariness..

1. Boreal forests catch fire on hotter/higher CO2 (like they are in California now)

2. Temperate areas get terraformed to deserts if possible

3. Health heals slower, or not at all on high CO2 due to environmental effects

4. Sources of fire increase their sparking distance in which flammable things catch on fire easier. Encourages easier spread of forest fires and player-crafted fires.

5. Water turns acidic, and deals slow damage. (Like the coral reefs)