As you point out, there have been periods in geological history where greenhouse gases were more abundant, and temperatures were much higher, and life still flourished. Also, as I've pointed out before, our planet's history shows its ability to survive numerous astronomical and tectonic shocks, some of then quite catastrophic, without a total collapse of the ecosystem. This suggests that there are numerous feedback mechanisms that buffer changes in our environment and allow a new equilibrium to eventually be established. Although it is conceivable that some runaway process might be unleashed that would turn us into another Mars or Venus, I do believe that is unlikely. No doubt a point might be reached that is beyond the ability of Gaia to control, but it hasn't happened yet, at least not since multicellular organisms first appeared a half-billion years ago.

The dilemma we face is not whether the earth will become uninhabitable, but whether it will undergo changes so extreme, and/or so sudden that we cannot adapt to them as a global civilization. Genus Homo thrived during the ice ages, with only paleolithic technology, but can we? After all, the Inuit were able to settle and prosper in the Arctic, but we can't, unless we import everything we need from warmer climes. But a complex civilization like ours can be overwhelmed, if the change is too extreme, or too sudden. Its happened before. Cultures have vanished because of long term droughts and other "natural" phenomena. Some of them even left ruins that are essentially intact, but they couldn't keep it going.

I believe the Greens have exaggerated the gravity of the problem, and their responses are simply not practical, or even realistic. But their ideological opponents who simply deny there is a problem, or blame it all on a conspiracy of their political enemies and economic rivals, are worse than mistaken, they are irresponsible, if not downright criminal. I am simply astonished at the magnitude of their corruption.

I believe we can get through this crisis, we are clever and adaptable, and we can organize ourselves and our technology very effectively when we get scared enough. But if we simply choose to do nothing, or wait till the situation becomes intolerable, we may not have the time and resources to fix the problem. The longer we wait, the harder it will be to find the solutions, and the longer it will take to implement them, and the more expensive they will be. We are blundering into uncharted waters and we need to throttle back and start coming up with a bunch of Plan Bs, not simply redline ourselves into the future.

My opinion is we won't pull it off. We will suffer a severe setback, and our civilization and technology will slip back to a "simpler, more romantic" (but certainly more squalid) level whether we like it or not. Then again, we may not be able to cut back to a less complex existence. Maybe when the slide comes, we won't be able to stop it. After all, how many of us today know how to grow food and fiber with nineteenth century methods? How many of us know how to make metal tools from mineral ores? Or make bricks? How many of us know how to weave cloth, or tan leather, or raise livestock, or build ships, or any of the things any medieval village could do a thousand years ago? For that matter, how many of us can start a fire without matches?