They think that the earth - Gaia - is a living creature, and that humans are a plague upon the earth. They point out that illnesses and plagues can exist for a long time, before reaching a mass and breaking out and doing a lot of damage. That is what we, humans, are doing.
Yes, it IS an odd theory.
Pas few days Drudge had a link to a story about obesity destroying the earth. Homosexuals like their partners lean.