There is a difference between a) not going along with something is considered "doing something" and b) rejecting an existing "doing something" Treaty that only 2 other countries did not sign, that has minuscule economic impact ... without having a replacement.

That (b) is what happened. That means Trump doesn't think something must be done - which means this administration does not care about climate science and it's predicted (and proven with current findings) disastrous impacts.

There is no alternative - either we begin to fix the problem with a global framework, or we suffer the tragedy of the commons on a global scale - and we're already seeing the effects of global temperature warming and ocean acidification.