Worst-case scenario is we just wipe out humanity, planet will be fine, it'll find a new equilibrium and carry on. Planet earth dont care if it has humans on it or not. I'd feel bad for all the human-dependent species though, what would they do without us?
This, the arguement that man-made climate change and pollution will lead to the death of all life on the planet is pretty weak. A severe enough nuclear winter, sure, and even then bacteria and probably even insects and a few mamals, birds, etc and flora would survive. Not to mention the vast reservoir of life that are the planet's oceans. It might take millions or even billions of years to return to the current biodiversity, but time isn't exactly something the Earth lacks. And the concept of time over such a long period is meaningless to anything but humans as far as we know. What's billions of years to a single-celled organism?
It does seem like a popular arguement for blatant misanthropes who perceive humanity as a destroying virus. Humanity isn't worth saving anyways, just other untainted, innocent life forms.
Although I have to agree with Leshma that even if the most horrible projections are accurate (and not another Malthusian Catastrophe bullshit colored entirely by politics and guesswork) one of the only good results from it will be forcing humanity out into space. We've only barely touched our toes in it and that was largely as a result of a dick measuring contest between the two most powerful countries in the world at the time. If NASA had as much fervour and funding behind it today as it did in the 60's I'm sure we'd be amazed by the results.
Hopefully the chinese will start challenging the americans in space soon, that should light a fire under their ass.
The ideal would be a multinational organization with prioritized funding, but it's never going to happen unless it's absolutely necessary, i.e it's crystal clear the planet cannot sustain any more people at the current level of technology.