The key items are on p. 16: first, that the "likely" range of equilibrium climate sensitivity is 1.5 - 4.5 C (which is the same as the first report in 1990--we have learned nothing in 28 years), and second, the footnote at the bottom of the page: "No best estimate for equilibrium climate sensitivity can now be given because of a lack of agreement on values across assessed lines of evidence and studies".
First, this raises the question: if there is lack of agreement, how did they even come up with the "likely" range? How can they say anything at all? And second, since the climate sensitivity is a key input to the models, how can the models possibly be valid?
http://www.ipcc.ch/report/ar5/wg1/
The key items are on p. 16: first, that the "likely" range of equilibrium climate sensitivity is 1.5 - 4.5 C (which is the same as the first report in 1990--we have learned nothing in 28 years), and second, the footnote at the bottom of the page: "No best estimate for equilibrium climate sensitivity can now be given because of a lack of agreement on values across assessed lines of evidence and studies".
First, this raises the question: if there is lack of agreement, how did they even come up with the "likely" range? How can they say anything at all? And second, since the climate sensitivity is a key input to the models, how can the models possibly be valid?