I think mankind is capable of some pretty bad stuff to the environment ,and yet when people have stood up to it things have changed for the better.
I grew up in Adelaide Australia and over 50 years ago I can remember the city zoo dumping their polluted water into the river Torrens ,the Chemical works at Port Adelaide with pipes coming out of it into the back reaches mangroves ,you could'nt fish there. Now there is a housing estate near there.
Large clay pits around Beverley 70 to 80 feet deep were filled with rubbish ,one even had a dirt levee bank 40 feet down where they just dumped thousands of litres of sump oil and buried it . I could go on but things got fixed but with global warning it's not so obvious to be convinced it's that bad yet.
I do think crooked politicians use this to rob the public and people get carbon credits for planting trees ,but thats for the wealthy in a lot of cases and they grow them on perfectly good cropping land not on poor farming land where they should , it's only about the money.
It's hard not to be cynical.