Whatever is happening, is happening thanks to the people of Earth - we do not need extraterrestrials to do it for us.
A few ways we are doing it:
Chemtrails
H.A.R.P
other ways are just because we do not self-discipline ourselves...like using plastics where we do not need to and then letting plastic destroy our eco-systems.
I'm not saying ETs do not exist. I believe they do, but if we are to believe just a fraction of what we are told, there are more than one species visiting us - so why would all of them allow one of them to alter our planet to suit them?