The concept of Climate Sensitivity (CS) is a useful way to describe the effects of carbon dioxide on the climate.  CS can be derived either from climate models or empirically – with the hope that the two results are concordant.   Let’s look at models first. Some 30 years ago, the National Academy of Sciences set up a group under MIT meteorologist Jules Charney to study this problem.  Their report arrived at a CS value of 1.5 to 4.5 degC of global climate warming for a doubling of atmospheric carbon dioxide.  One immediately notices the huge uncertainty, a factor of 3.  Yet the climate forcing of CO2 is known much more precisely.  The explanation for this wide uncertainty range of CS lies in our imperfect knowledge of (1) feedback from clouds and from water vapor (WV is the most important atmospheric greenhouse gas) and (2) the radiative effects of aerosols in changing the albedo of the Earth atmosphere and thereby the amount of...(Read Full Article)