Nice discussion all. Just some thoughts...
but to be clear .. we are not frying our planet ... global warming is a natural phenoenom .. has happened many times before .. we just weren't around at the time ... the concerns are that we may be speeding it up ... I would hope we are speeding it up .. as the last global warming happened without such a populus on the planet i'd hope that having howveer many billion humans living here has some sort of effect on the world ecosystem, otherwise we really are insignificant.
And the speed at which the planet changes is exactly where the problem is! Most species have what it takes to survive temperature changes (as they did for millions of years), but only if it happens at a time scale compatible to what happened in the past. If it is too fast many will not be able to survive.
Take the dinosaurs for example, they survived for almost 200 million years (we humans have been around for less than half a million), and why did they go extinct? There were many catastrophic environmental changes during their 200 million year history, but something was different about what happened 65 million years ago (the so called KT boundary). Several theories are out to explain it, and most of them offer different explanations, but all have something in common, whatever caused the extinctions happened in a blink of an eye in terms of geological time scale (or a few hundred years).
So, it really doesn't matter if the planet was this warm or even a lot warmer before, the real questions is, were the changes ever this fast?
