Acid rain?
AFAIK acid rain and global warming are separate things. Global warming is caused mostly by CO2, while acid rains are caused mostly by SO2 and NOx.
SO2 and NOx are very nasty due to their tendency to form sulfuric and nitric acid, hence acid rains. However, they also cause global cooling by reflecting incoming radiation.
It looks like that mod is not really about global warming but pollution in general, which is fine, but calling it "global warming" does more harm than good IMHO.