I had been seeing signs of progress from Andy Revkin, but the scratched side of the coin came up this week. Check this article.
I would encourage Mr. Revkin to post a Dot Earth blog entry in which he QUANTIFIES the following:
1) “A big buildup of greenhouse gasses”: Please restate, in ppm of atmospheric CO2.
2) “A long-lasting and very disruptive shift”: Please specify the exact nature of the one or two most-serious disruptive shifts, and QUANTIFY the minimum degree of this risk. For example, if the “disruptive shift” is future flooding and droughts, specify the predicted annual agricultural output in the period following this “disruptive shift”. “Long-lasting” to be quantified in number of decades.
3) “RISKS”. For each most-serious disruptive shift specified in (2), state the probability of this shift, as a range. For example: Probability range = 0.1 to 0.5. Or, probability range = 0.01 to 0.10.
4) Present the “consensus climate science” that substantiates the RISK probability range specified in (3), to the 80% confidence level. Presumably this consensus climate science is available in an IPCC publication.
This begins with the not uncommon confusion is the idea that the amount of greenhouse gases in the air is a quantity not under conscious control. What will be depends crucially on what we do. (Think of Scrooge’s question to the Ghost.)
The most extreme risk envisioned in all climate studies is surely a runaway greenhouse effect, in which human activities cause a buildup of CO2 to a level (ca. 1400 ppm). In this condition, as hot as it would be and as much as the patterns of precipitation and other processes have been altered, large additional rises are unstoppable. Natural processes release massive amounts of CO2. Some are biological, such as rapid respiration of vast stores of organic carbon in soils globally by bacteria, activated by high temperature. Others are a-biological, such as ocean degassing from the lower solubility of CO2 in warm versus cool water and also melting of methane clathrates (ice with trapped methane, which is more potent than CO2 as a greenhouse gas. There is good evidence of past runaway greenhouse events. One or more ensued as the recovery from Snowball Earth episodes (a fascinating story, but there is no room to detail this here). Another is themid-Cretaceous period, when CO2 has been inferred to be as high as 3000 ppm (very indirect evidence, such as from the structures of plant leaves). Ocean temperatures as high as 38 C (100 F) are inferred. This level would be lethal to us; dinosaurs prospered in what Richard Alley from Penn State has called the “Saurian Sauna.”
OK, that is some scary stuff. It’s not “runaway” as on Venus; the ocean does not boil off, but geochemical feedbacks act to take us into territory far beyond normal, far beyond what complex terrestrial life can handle.
“(For what it’s worth, I agree with Yohe’s assessment, although I differ with his preference for a rising price on carbon as the most feasible way to develop an energy menu that works for the long haul.) “
(Lest I be misunderstood, Yohe is not the one talking runaway. That isn’t the point, really.)