Take a look and answer one simple question.
http://www.nature.com/nature/journal/v446/n7135/extref/nature05699-s1.pdf
Would you send your kids to either Wesleyan or Yale?
This link (below) shows the best estimates of temperature over the past 540 million years (chart is too big to paste.)
420 million years ago was about 4C warmer than today. (I believe this is based on Berner's own estimate from GeoCarb).
His CO2 estimates would represent 4 doublings of CO2 so they are clearly saying the senstivity to CO2 is on the very low end of the estimate - probably under 1.5C (rather than between 1.5C to 6.5C) for a doubling of CO2.
http://en.wikipedia.org/wiki/Image:All_palaeotemps.png
It is certainly NOT 3C for every doubling (which would make the temperature 420 million years 12C higher than today and certainly not 6.5C for every doubling which would put the temperature 26C higher than today.) Once again, 4C is what Berner's own estimates say or about 1C for every doubling.
He probably needed to downplay the result (while still publishing his research) so he could still get invited to all the great global warming parties (if you know what I mean).
