... Even a cursory glance at paleoclimates that were warmer than today ...
Yes, that is true and even the atmospheric CO2 levels have been several times higher than they are today with life surviving. Thus, you and many others conclude that while “global warming” may be inconvenient for some and a blessing for others (lower shipping cost with ice free Arctic Ocean, more useful Siberia, etc.) it is no threat to life on Earth.
What this POV ignores is than the RATE of CO2 release with burning of fossil fuels is hundreds of times faster than ever before in Earth's history. This may convert Earth into a cooler version of Venus with a high pressure steam atmosphere - a completely sterile planet.
There is a thread called “apocalypse soon” (at
http://www.sciforums.com/showthread.php?133084-Apocalypse-Soon) in which I have disputed the OP's idea that “peak oil” will make such damage to the economies of he world that > 95% people will die. I argue that man is adaptive and there are already well known technologies for societies to run on solar energy at quite affordable costs. For example as Brazil* now mostly does and the entire world could as I show in post 1436 of that thread. (many pages back now).
But what I want to call your attention to is how the earth may switch to its hot stable state as Venus did some millions of years ago. I. e. a state with IR opaque atmosphere, making the surface temperature of Venus above the melting point of lead. Some of Earth's metals would be melt too if Earth were in its “Hot Stable State”
Methane, CH4, is a GHG at least 10 times more effective at blocking IR radiation from escaping into space than CO2 is. In Earth's past the “global warming” was much slower than now with man's rapid burning of fossil fuels, and thus the release of CH4 stored in methane hydrates was much slower – so slow that the atmospheric destruction of CH4 kept the concentration of CH4 in the air very low. That is not the case now – the CH4 concentration is rising long with that of CO2.
Recently, in the shallower Arctic Ocean where water is warming rapidly, methane hydrates are decomposing, releasing CH4. I.e. kilometer diameter “clouds” of bubbles of CH4 are rising up to the surface and then entering the atmosphere. Fortunately CH4 is destroyed by atmospheric processes with a half life of only slightly more than a decade. Unfortunately, there is more carbon stored in the methane hydrates than ever was stored in all the coal and oil!
There exists the real possibility that we have already activated two positive feed back loops that may make Earth sterile in a few thousand years. I. e. the unprecedented rate of CO2 now making an unprecedented rate of CH4 release from methane hydrates is self accelerating process. If the “loop gain” of these feedback loops is already greater than unity, EARTH WILL SWITCH TO ITS HOT STABLE STATE. If the loop gain is not yet greater than unity it may be possible thru reduction of the RATE of CO2 release to prevent a thermal run away of Earth's surface temperature.
I posted some of these concerns in the above thread as a completely sterile Earth with a high pressure steam atmosphere would be a real catastrophe and “peak oil” is only an inconvenience, requiring more utilization of solar energy. See first post1056, and then 1061 of the above link.
* Less than 5% of Brazil's electrical energy comes from fossil fuels. ~85% is hydro-power, more than 5% is thermal steam made by burning the sugar cane after it has been crushed and supplied the distillation of alcohol heat requirements, wind and solar PV make a few percent each and Brazil's one nuclear site makes about 1%. The sugar cane alcohol not only fuels Brazilian cars but also now Braskem is making 400,000 TONNES of plastic annually from sugar cane, not oil, at lower cost than oil at $90/ brl or greater.