You know what one thing is at fault for all the problems humanity has caused in the world? Nature. Pure and simple, nature. This destructive tendacy we have? Every single bloody creature in this whole world has that inbred in them - a desire to survive and, when that is achieved, for ever more power. Put any organism into a system free of predators, and it will multiply and destroy. Nature is cutthroat, and nature is what gives us these problems. If you look at it in the context of the earth as a whole, it is a flaw in the system. Far from humans being some sort of aberration to the earth (say, the Chrono Cross hypothesis), far from being enemies to the planet, we are the fullest culmination of what nature breeds. WE have not messed up the planet, nature has - nature working within us, that is.
That said, this planet and all the other creatures are bloody fortunate that in one manner we are at least different than they, and it is not destruction. It is in the ability to consciously change. Humanity is not the problem, per say, nature is. Nature has given us this destruction, given us these problems, and is the root for most anything - including wars. We have the ability to know nature, and to act apart from it. In some manner, we are the only hope to what nature screwed up, and the potential saviours of the world.
So, yeah, global warming and all, that's a problem. Definitely. But I think we should put the blame where it's due, and then think better of ourselves. It's nature's self-destructive hand within us that has caused it, but we're given this marvellous opportunity now to, in acting contrary to nature (ie. for the betterment of all, and not merely in self-service, as all other organisms do), show our worth as truly above the animals. It'll help ourselves, to be sure, but to act with a thought for everything is our gift, and our mandate is to be noble guardians of a very chaotic nature.
