If you believe this, wouldn't the ethical thing be to not have kids?
Besides, global warming-derived refugee flows into Europe could well put it in a much worse position than the US.
I see this over and over . . . If you don't have kids, who exactly are you saving the world for?
Why do you see 'saving the world' as a priority? The natural (non-human) environment doesn't have any right to exist. Our priority should be to avoid harming humans, and people born into a world that's mostly uninhabitable for them will have pretty shit lives.
Long term, the world will be fine, we won't.
The billions of people (including kids) who already exist. Whether through adoption or supporting better general social programs. Clearly if that were the focus and the way humans thought the world would be a better place. But of course it's wishful thinking and people have every right to have and enjoy their own children.