The “runaway greenhouse effect”: James Hansen vs Gavin Schmidt

References to "tipping points" and the specter of a "runaway greenhouse effect" or "runaway global warming" can be found EVERYWHERE in AGW alarmist writings. It’s on blogs, it’s in the news and, most importantly, some of the most prominent climate scientists invoke it. There’s no denying it’s a favourite bogey-man and scare tactic.

On the other hand many AGW true believers know full well that predictions of a runaway greenhouse effect are over-the-top alarmism with little theoretical or evidentiary basis. On occasion an AGW skeptic will point to evidence that shows such predictions are unfounded. The response of the AGW huckster is to berate the skeptic for bringing the subject up and to deny anyone thinks it a problem.

An example of the latter can be found in this RealClimate comment thread:

Comment by Don Healy (19 August 2008 at 11:31 AM) : [...] ... Another question that comes to mind is if earth did not experience a runaway greenhouse effect when CO2 levels were 4000 ppm or higher in earlier geologic history, what has changed to create such alarm at levels ten times lower? Just some random thoughts from one whose background is in forestry and plant physiology.

[Response: No one is predicting a runaway greenhouse effect in that sense (this is one of those trivial talking points alluded to the post). ... Please be serious. - gavin]

Note: "gavin" is Gavin Schmidt, a climate modeler at NASA/GISS and co-founder of the RealClimate blog along with Michael Mann et al.

An example of the former (alarmism) is in this article featuring prominent climate scientist alarmist James Hansen (Director of Research at NASA/GISS and, presumably, Gavin Schmidt’s boss) shrieking about a runaway greenhouse effect:

"If we burn all of the coal [on the planet], there is a good chance we will initiate the runaway greenhouse effect," he said. That runaway greenhouse effect could become unstoppable, eventually boiling the oceans and destroying all life on earth in what Hansen called the "Venus Syndrome," after the conditions that exist on the planet next-closest to the sun.

"We already probably have CO2 past the tipping level that would cause some effects like the loss of arctic sea ice,"

So we have two colleagues (boss and underling) at the same government organization positing two wildly different views about a runaway greenhouse effect. Though Gavin Schmidt sensibly downplays the credibility of the notion of runaway global warming he’s absolutely wrong when he says no one is predicting it - his boss is, for one. And Schmidt weasel-worded his reply saying no one is predicting it "in that sense". If not "that sense", what sense? He doesn’t say, but perhaps he means the sense that his boss, James Hansen, is using - the alarmist propaganda sense.