Further, that these warmer periods did not cause runaway warming, although from all that the current alarmists say, they should have. If man-caused warming triggers positive feedbacks - increased water vapor traps more heat, more heat increases water vapor and generates more release of CO2 from oceans and methane from thawing permafrost - then previous warming should have done the same.
More proof of that, or the lack of runaway warming, is clearly shown in a recent video.
The video is great, but for quiet contemplation of the graphs showing previous periods of greater natural warming compared to the present, go to "Hockey stick observed in NOAA ice core data."
Click on this graph showing periods of climate change during the past 10,000 years. Of interest are the two periods of greater warming during the past 2,000 years - the Medieval Warm Period of about 1,000 years ago, and the even warmer Roman Period at year "0". So much for Al Gore's claim that the current warming is "unprecedented."
Obviously Al learned from Bill Clinton how to parse the truth. What Al meant to say is the current warming is unprecedented if you only look at the last 1,000 years, and then only if you use the discredited "hockey stick" prepared by Michael Mann of "Climategate" fame that eliminated both the Medieval Warm Period (850 to 1350AD) and the Little Ice Age (1350 to 1850AD).
In other words the current warming is unprecedented if you only go back to the Little Ice Age, or if you hide or overlook all the previous warming periods. For example, the graph shows at least a dozen in the past 10,000 years warmer than the present.