6/30/2014 10:00am by Gaius Publius
One of the greenhouse gases (GHGs) that Obama’s EPA Clean Power Plan doesn’t count is methane from leaks, for example, fracking leaks, fuel line leaks, transportation leaks, and so on. Yet methane (CH4) is one of the most powerful greenhouse gases known, though very short-lived (most atmospheric methane disappears in about 12 years, becoming CO2 and water vapor).
And one of the cornerstones of the idea that mankind still has a “carbon budget” — that we can still release even more CO2 and other greenhouse gases like methane, though a “limited” amount — is the idea that we can do a good job of modeling climate-changing feedbacks. We can do a good job of modeling some feedbacks, but we’re very bad at modeling others, and some feedbacks have so much randomness about them that modeling them becomes next to impossible.
For an example of seemingly good models that have gotten things drastically wrong, take a look at what 13 Arctic-ice models said about the ice melt rate (loss of ice is a feedback, since it’s cause by warming, and then feeds more warming back to the system):
Loss of summer Arctic sea ice, modeled vs. observed (source here; adapted from Fig. 1 here)
All of the fuzzy lines are predictions of various models using the assumptions of that model. The heavy black line is the mean of those models. The red line is observed loss. Note that today, we’re about at the place the IPCC models had us reaching 90 years from now. The observations peak at about 9 million square kilometers, and we’re now at about 3 million. When we reach 1 million square kilometers, the Arctic will be considered “ice free.” Not long after that, summer ice will go to actual zero. With increased warming, winter ice will go to zero also.
See why I’m always saying we’re “wrong to the slow side”? If you think a climate event will happen in some number of years, cut it in half, at least, and maybe in half again.
For an example of a process that’s almost impossible to model, consider the disappearance of Antarctic ice shelves. They don’t go gradually; they hang around, then go suddenly and in big chunks, as they have recently. We’ve crossed the point of no return on large parts of the Western Antarctic shelf. No one saw that coming when it did, and there was no way to model it. That system is just too complex, with too many unknowns.
Global Climate Change