The Unassailable Math of Climate Change: Gaius Publius Interviews Michael Mann

Naked Capitalism posted yesterday an interview by politics blogger Gaius Publius with climate scientist Michael Mann. The interview is a good primer on the carbon math of global warming. The standard marker established by the Intergovernmental Panel on Climate Change (IPCC) is +2°C warming. As Gaius Publius says,

Most still think that 350 ppm (parts per million) CO2 is what’s needed to keep us at the upper end of Holocene (era of civilized human culture) temperatures. [Like Bill McKibben's 350.org.] For contrast, the ice ages averaged about 180 ppm CO2 at the bottom, and pre-industrial (pre-1750) concentrations were about 280 ppm CO2. Pre-industrial temperatures were at the bottom of the Holocene (post–ice age) temperature range, so there’s some headroom above that 280 ppm number. How much exactly? No one knows. 

It looks like we’re headed for a IPCC-”safe” 450 ppm CO2 unless we stop. Not safe, in my opinion, nor in Dr. Mann’s. For starters, this “450 ppm” measures CO2 only, not other GHGs like methane and nitrous oxide. The effective ppm in “CO2 equivalent” with those other added GHGs is higher if only CO2 is at 450. 

It’s thought that the original ice sheet formations of 35 million years ago, which gave us modern Antarctic, Greenland and Arctic ice, occurred in a cooling environment that crossed roughly below CO2 concentrations in the range of 550-400 ppm or so. 

First, that’s a wide range. Second, that’s no indication of what will happen going the other direction, where the warming tipping points are. Hansen writes, correctly IMO, that real climate sensitivity depends on (a) the starting point (i.e., how near we are to tipping points), and (b) the direction (effect of warming of X amount is not necessarily correlated to the effect of cooling of that same amount). 

Nevertheless, the massive uncertainty, plus the world-historical consequences, gives most of us pause. I personally worry that 450 ppm CO2 is ultimately a death sentence for civilized humans. Back to life as hunter-gatherers for our third- or fourth-generation descendants. And if worldwide social chaos takes over before we stop, the process could run to conclusion, which, the old IPCC A1FI scenario says, tops out at +7°C warming.

Science is a story based on measurement. For climate-science deniers, where's the math? What about the massive ice-sheet melt? To deny or ignore the science is to repeal the Enlightenment, pitching us backwards to the days when the churchmen ruled a flat Earth. That's what the ISIS response to the Arab Spring is all about, and what is planned for us all if certain reactionary political formations (like those backed by the Kochs) have their way.

Check out the Gaius Publius-Michael Mann interview.