Selfish moment here: if the world is totally fucked, it won't be within my lifetime.
Re: humans being able to ruin nature. Yes. Humans are damn powerful. Go stand next to a skyscraper or watch nuke footage and then tell me humanity doesn't have earth-shaking power. Nothing like us has been seen before on earth.
However, I think it's likely that the world powers will finally take decisive action before the problem reaches a crisis point. From all the studies I've read, global warming, if it is indeed a threat, won't begin to cause real harm for several decades and possibly over a century; global average temperatures have only risen one degree in the last hundred years (some regional averages have actually fallen by a degree or more) and will not be likely to increase by more than a few more in the next hundred. It won't be catastrophic unless we see a rise of over ten degrees, and it is almost universally agreed among researchers that such a thing will take quite a long time - long enough for governments to take their time fixing it and still manage to save the world.