Plants Need CO2 To GrowFebruary 27, 2012
Bigfoot, the Loch Ness Monster, and High Climate Sensitivity
Source: World Climate Report
A few months ago, we reported on a paper in the scientific literature (Schmittner et al. 2011) that concluded that there were only "vanishing probabilities" that the value of the earth's climate sensitivity-the amount of global temperature change resulting from a doubling of the atmospheric carbon dioxide content-was above 3.2°C, and that a climate sensitivity exceeding 6°C was "implausible." Now, a new paper has been published (Olson et al., 2012) that finds that the 95% confidence range for the value of the earth's actual climate sensitivity extends only to a value as great as 4.9°C. This is yet another in an expanding list of papers that strongly suggest that that the IPCC entertainment of the possibility that the earth's climate sensitivity is extremely high (say, greater than 5-6°C, is wrong).
As apocalyptic climate change lurks among high sensitivity values, these new findings virtually eliminate the places where it could be hiding-and relegate talk of apocalyptic climate change to that of Loch Ness monsters, big foot, and woolly mammoths in Siberia.
It turns out that the "priors" have a large influence on the final solution. In other words, if you already have some rough idea of the range of potential climate sensitivity, that rough idea can help guide you to a better solution when new, relevant data become available.
Back in 2007, when the Intergovernmental Panel on Climate Change (IPCC) published its Fourth Assessment Report (AR4), the IPCC decided that instead of using an "expert prior" (that is, one that was guided by a rough guess) to help guide its determination of the distribution of possible climate sensitivity values, that it would use a "uninformed prior" (that is, as it sounds, one which adds no previous knowledge). The uninformed prior used by the IPCC was a uniform prior-the IPCC assigned an equal chance that the climate sensitivity could be anywhere in the range from 0°C to 10°C. This choice seems somewhat absurd in light of the fact that ever since the first IPCC report, from back in 1990, the IPCC has issued a rough guess that the climate sensitivity was somewhere in the 1.5° to 4.5°C range. You would think that their own "expert" assessment would be better than one that was "uninformed"-but perhaps that tells you something about how much credence they put in their own expertise!
** For additional peer-reviewed scientific references and an in-depth discussion of the science supporting our position, please visit Climate Change Reconsidered: The Report of the Nongovernmental Planel on Climate Change (www.climatechangereconsidered.org), or CO2 Science (www.co2science.org).