What would Jesus do other than sit back and watch?

An asteroid is going to destroy the Earth long before any GLOBULL WARMING does...

Jesus has already told us what He is going to do, and that ain't it.

and what is?

Given that this is recounted in both the Old and New Testaments, you are asking a question that would take some time to cover. Do some research on what happens during the Tribulation if you really want to know the answer to your question.

This is also a basic start: https://www.gotquestions.org/when-Jesus-returns.html