Jim Hansen's latest estimate of the sensitivity of climate to approximately doubling CO2 is bound to arouse controversy, so I've revised this precis of past estimates- the original compilation by Levenson did not include Arrhenius second estimate, published a decade after his first set this Victorian roller coaster in motion.
19th century climate sensitivity estimates were woefully uncertain, meandering over a range of nearly ten degrees F per decade.
But thanks to modern science -- 112 years of continuous theoretical progress, ever more accurate instruments, exponentially growing computer power and sophisticated climate models, expert estimates can now shift by nearly ten degrees F in a single year! Hence the importance of the latest result.
Who would be so cynical as to point out that starting in 2005, the misallocation of emissions quotas by the European Union's Emissions Trading Scheme led to a collapse in the price of carbon permits--a market Al has been instrumental in establishing -- from $40 to 40 cents?
At which price no incentive to reduce emissions exists. Except for newer and more elegant estimates of climate sensitivity , conveniently blasting off in the direction carbon traders would like to see the market travel. Stay tuned for the next exciting statistic, and the sequel to Six Degrees coming soon to a PBS channel near you.
Right now I have to run off to Harvard's Kennedy School for Prices vs. Quantities vs. Bankable Quantities for Stock Pollutants by William Pizer of Resources for the Future; next week's seminar will be Measuring the Distributional Impacts of Carbon Pricing http://isites.harvard.edu/icb/icb.do?keyword=k19826.