What proofs are there that non-eco friendly practices harm the environment, and in what way?

I'm not an anti-environmentalist, I actually recycle, and assume that we can't keep using natural resources at the rate we do. But what proof is there? How does anyone know that recycling isn't just completely pointless? I'd really appreciate an educated answer. Any examples would be nice. What evidence is there that we can't just ravish all of the worlds resources with no effects? I know we put catalytic converters to help localized air quality, but what proof is there that that is even harmful?