Nature's Cycles
Of course, the bigger problem is whom do we blame. But I fear that would be a whole nother topic altogether. Which brings me back to the original idea.
I have come to the conclusion that it truly is cyclic. It, in this case, meaning the environment. Every billion or so years, an intelligent race rises up and screws up the planet so horribly that their race is entirely wiped out along with a good part of the planet. Then, over a billion years' time, give or take, all traces of that civilization are totally wiped out. Ice ages and the such. Hell, even radioactive waste would be fine by then.
That's when, of course, a new race rises up.
And in 5 billion years, give or take, the Sun will supernova and we will be blown to radioactive dust which will slowly colalesce into a new planet under a new sun. And that, too is cyclic.