Not done with that, yet. A very educational post here.
We have discussed the http://home.wanadoo.nl/bijkerk/medieval-warm-period.pdf . I have shown that at the end of the first millennium multiple proxies all over the world show warming, without balancing cooling, convincingly challenging the SPM about the second half of the 20th century being the warmest 5 decades in the last 1300 years.
The obvious problem is that natural factors, without greenhouse gasses could cause more warming than today, making the global warming idea very doubtful
Then we have mentioned the Holocene Thermal Optimum, rougly 9000-6000 years ago, when http://www.sscnet.ucla.edu/geog/downloads/634/270.pdf and this happened when the CO2 was stable but lower than today. But we had a waning summer insolation maximum of the Northern Hemisphere (milankovitch cycles), so that seems to make sense. However the Holocene thermal Maximum was also evident on the Southern Hemisphere:
http://tinyurl.com/2tlgy3
http://tinyurl.com/3b7uz3
http://tinyurl.com/2s3dwq
http://tinyurl.com/358w3l
http://tinyurl.com/2w86g8
It must also be noted that both the Greenland Ice Sheet and the Antarctic Ice sheets survived this millenniums long warmer periods without any problem challenging the melting scare. So besides solar insolation which opposed warming on the southern hemisphere and the CO2 much lower than today, there was still natural variation making it warmer than today.
Then we have the previous interglacial period the Eemian, Ipwichian or Sangamonian some 120,000 years ago.. This was when the
hippopotamus swam in the Rhine in Germany and in the
Thames in the UK suggesting sub-tropical conditions in areas currently with moderate climates. Would be tough to state that this period was not warmer than today. The CO2 levels were lower of course, comparable with the pre-industrial times.
Incidentely, one of the warmest periods in the distant geologic past is considered to be the early Tertiary Paleocene era from 65-55 Million years ago. How about its CO2 levels? Comparable to today!:
http://www.sciencemag.org/cgi/content/abstract/292/5525/2310
http://droyer.web.wesleyan.edu/royer_dissertation.pdf (fig 4.3 page 102 of the PDF count)
Double source showing robustness of the stomata method.
http://home.wanadoo.nl/bijkerk/CO2-KT-PETM.GIF
So it is obvious that the natural variability in climate is grossly underestimated in the Summary for Policy makers. It can be warmer than today, without excess CO2 and without increased orbital forcing. It may also be noted that this is not foreseen in any model, so it can’t reproduce it either. Nevertheless, this variability shows that CO2 is not necessarily a major climate driver if at all.
Why is this chapter neither in the SPM nor in the ISPM?