I think the main issue at hand is the overall warming of the planet, the continuing increase in unusual weather (i.e. last year's hurricane season), the rapid destruction of habitat (which is all us), the increase in pollutants (which is us), and it is a simple issue of logic that the speed that we have polluted, destroyed and changed the planet will have us careening into uncharted territory as far as climate is concerned.
You spoke of cycles, those cycles were the natural balancing factors of which there are none anymore. The natural biosphere can only handle so much extra stress and I think we are reaching those limits.
Of course, the other way of looking at it is that those animals that can adapt to lead, mercury, chemical, lack of rain where it has rained for centuries in a regular pattern are the only ones that deserve to survive, but think of the creatures that we will lose.
