Sin = decay
God said everything would die/decay if sin was committed....it was...so there you go.
Our entire environment is out of wack causing all manner of earthly problems.

And...I have already given the answer to your questions.

To be even more specific, satan is the prince of this world...he seeks to devour humans and destroy them...he causes all manner of destruction.
Like I said at the very beginning....WHO do you think causes evil things??