Dead Parameters Walking
" Climate sensitivity" , notes Barton Paul Levenson ,
" Is an estimate of how much some factor in a regional or global climate would change with a specific change in some factor affecting it. That's pretty vague, of course. In practice, the term has recently come to mean the change in Earth's surface temperature that could be expected if the ambient level of carbon dioxide were doubled (usually from the preindustrial level of 280 parts per million by volume to 560 ppmv, but sometimes from 300 to 600).
Below are all the estimates I could find in the literature. Not all estimates are equal. Most of these, though not all, include the effects of climate feedbacks such as water vapor. And these estimates include ones which were later shown to be based on flawed models, erroneous reasoning or outright mistakes"
Estimate of its value vary with scientific sophistication and taste , the peer-reviewed values spanning nearly two orders of magnitude , since the first was put forth by Arrhenius in 1896. While reasonably complete treatments of the physics have converged into an idealized mathematical consensus, the choice of variables needed to connect the physics to a real planetary system remain , empirically, well controversial- witness Levenson's cautionary graph of how the published ones look over time.
Arrhenius first result testifies to the force of his physical intuition- he got the order of magnitude right with no computers and crude spectrometers -Victorian infrared prisms were carved out of rock salt. But modern instruments , billion dollar R&D funding , and exploding computer power have not made the data scatter go away. The policy debate can't die until the data flatline, and the last decade's estimates of climate sensitivity values still span an order of magnitude.
It would be statistically perverse to point out that the trend of the four most modern values ( five counting Schneider's 2007 estimate, published shortly after this graph appeared) is not going up.
Lord knows which way the four year trend will point in 2020. Science aside, funding can be directed just as data are cherry-picked, and the cynically directed support of groups that deliver high or low end results can bend it either way.Yet there remains a big difference in the physics pecking order between the merely ornery and often wrong , and those few who prove their contraries -- I'm biased towards Schneider's conclusion because the last time he dared to be contrary, he proved to be right.
It is curious that the two values most closely approximating the production values of the latest National Geographic Special were respectively published in 1963 and 1896 !
Isn't modern climate science wonderful ?