You didn't go far enough: Air pollution linked to overpopulation. Overpopulation linked to high birth rates. High birth rates linked to sex. So in conclusion:

You didn't go far enough: Air pollution linked to overpopulation. Overpopulation linked to high birth rates. High birth rates linked to sex. So in conclusion: Celibacy cures depression and suicide. Of course, why stop there? We could keep going deeper.