I think your making a classic error in your thinking about past climate shifts. The resolution of a graph going back millions of years is always going to be lacking when trying to see details by the month. Also CO2 is "today" our big concern because its the gas we emit as a pollutant and one that is also a green house gas. But there are lots of gasses that can contribute to the greenhouse effect. Methane for instance. So although today CO2 is a primary "concern" its not the only player in the game.
The Greece analogy just doesn't apply because it effects a fiat currency system which can always be artificially corrected. The climate system took the entire might of the entire existence of the industrial age to alter. Its not like we can just sign a bill or law into effect and suddenly go back to the way it was. The idea that its a small player causing an emotional system to panic I'm going to have to take issue with as well. CO2 is our primary greenhouse gas, something like 60% of the greenhouse effect is caused by CO2, so a better analogy would be to say if the US, Canadian, S American, Australian and Euro economies combined went bust.
While I'd agree there seems to be an upper and lower limit to temp fluctuations the evidence supporting that is somewhat less than robust. I believe there is only one study that used several data sets to attempt to recreate the paleo climate going back over that 600k year period you mentioned. Although I think continuing work has brought that figure up to about 1m years recently.
The climate system will change due to a lot of factors, surprisingly, some of which have nothing to do with the atmosphere. Topography is one that folks often fail to consider. Before the break up of Pangea weather patterns over land were not so dependent on ocean dynamics, but now that there's more and smaller continents the ocean system comes into a larger role in climate. Also the topography of the ocean floor seems to make a big difference. Deep ocean currents are another big player.
for more on the oceans role and interactions check out the video lecture by DR Jeremy Jackson.
http://www.google.com/url?sa=t&rct=...NS3wxKQqgIFul5VmQ&sig2=v5AfaZZ6T9fwRjQw0hR06g
He's pretty much the wolds leading authority of the state of the oceans and since they play a vital role in the atmospheric chemistry I think its a must see if we are going to actually have an informed conversation. Which I appreciate by the way. Science never fears a polite devils advocate.
getting back to CO2 for a moment, the alterations in atmospheric chemistry that have occurred over the last 30 or 40 years aren't going to show up very well on a graph going back millions of years. But its important to remember that its the rate of change and not just the amount thats causing so much trouble. Yes its hard to go back millions of years and find spikes of 100 or less years, even 1000 but the climate system tends to want to change slowly anyway. With abrupt alterations being fairly rare.
If there is a cap to the range of fluctuation in temp, which I agree there should be in this type of system, then its a reflection of the feed backs in the system, which take time to have there effect. IE if you alter the system to quickly in any one parameter its likely; and there does seem to be a lot of evidence supporting this, that a bounce effect is realized throughout the system. So I don't think those parameters are set in stone. I'd use the snow ball earth event as an example. Things got mighty chilly way back about 600m years ago.
CO2 is today our primary concern because its the one parameter we've altered much faster than anything we can see in the past. The speed of that alteration is a big part of the problem, had the same change occurred over a few million years it might not be such a big deal, but it didn't, and we are directly to blame for it. If you checked the link in my previous I think we must agree that science has very strong evidence. We and only we are to blame. We were at the top of the curve, if you look at the temp records over the last 1m years or so. CO2 in the natural cycle should have begun to slide downwards along with temp. Or at least it should have happened that way.
Didn't because we artificially increased the levels of CO2 and now levels of methane are up dramatically as well (150%). While its difficult to see the exact time frames involved the high Permian extinction event is pretty well studied and offers some real insight into what happens when these parameters have changed in the past. There's a pretty good video that, although its kinda old, touches on the original findings. Which have been further studied and are at this point enjoying a fairly high consensus.
I'm pretty sure its found in episode 2 part 4 of the video series, "miracle planet" but as I'm watching it there still talking about how it ended, not how it began yet, but its in there somewhere.
http://www.youtube.com/watch?v=NWl9...PL2676EBC05A1AA53D&lf=results_main&playnext=2