Black Swan Sighted in Climate Sensitivity

Despite the indefatiguability of denialists, most of the facts of global warming are exceedingly well established. We know that the atmosphere is warming (about 2F, on the average, in the Southwest). We know that six out of seven world oceans are warming (see this colossal study out of Scripps, led by Tim Barnett). We know that the earth is absorbing more heat energy than it emits, which is unequivocal proof of global warming right there. We know that countless species and habitats are shifting in an attitude to survive on a globe whose climate is evolving at alarming speed. We know that Arctic Ice cover is vanishing at a remarkable rate and will be ice-free in the summer within twenty years. We know that fires are becoming more dangerous and heat waves more severe — Phoenix could well become unlivable within our lifetimes, if you consider 122 degrees unlivable, and the mortality risk of heat waves is well-established. And so on and so on.

But despite considerable nervousness on the part of the experts, 82% of whom consider the IPCC’s alarming 4th report to be either fully accurate, or not alarming enough, we still tend to think that things in the future, when it comes to weather, will be like things in the past.

Are we blind? Are we fooling ourselves?

Probably so, argues a "quant"–an  exceedingly well-paid Wall St. statistician who makes a living by mastering stochastic (highly random, often large) changes in the economic weather. In a bestseller called The Black Swan, Nassim Nicholas Taleb makes a strong case for the fact that a single "improbable" change–or disaster–can have a decisive or devastating effect on our lives. Nobody Knows What’s Going On, he titles an early chapter.

Yet although ultimately his argument is mathematical, he begins with a personal story.Taleb grew up in Lebanon, a member of an extremely well-educated, prominent, and successful family. The Lebanon he grew up in was a "paradise." Beirut was known as "the Paris of the Mideast." Then when he was fifteen, a civil war erupted between Christian and Moslem factions in his country.

"I was constantly told by adults that the war, which ended up lasting close to seventeen years, was going to end in "only a matter of days."" writes Taleb in the book.

This devastating experience, among others, forced him to confront the possibility of abrupt change, and especially a change beyond our mind’s ability to absorb. The Black October stock market crash of l987, the rise of the Internet, 9/11 all served to convince of the central importance of these stochastic shifts.

"History and society do not crawl," he argues. "They make jumps. They go from fracture to fracture…yet we (and historians) like to believe in the predictable, small incremental progression."

The book symbolizes this idea with a black swan, because it’s a great example. For centuries the civilized world "knew" that swans were white. Then it discovered southern Australia, where swans are black.   

"One single observation can invalidate a general statement derived from millenia of confirmatory sightings of white swans. All you need is one single (and, I am told, quite ugly) black bird," writes Taleb in his prologue. In the book he alludes in passing to the possibility of a black swan in climate change change, but doesn’t pursue the idea. He is more focused on the possibility of economic disaster (a threat environmentalists certainly should not ignore). Yet the book makes a strong emotional and mathematical argument for considering bigger risks  in climate — an enviro disaster bigger than Katrina.

In mathematical thinking, Taleb disdains the Gaussian — bell curve — model as a means by which to analyze our lives, arguing that the small events of daily life mean little when put up against the huge changes that determine our fate.

"The traditional Gaussian way of looking at the world begins by focusing on the ordinary, and then deals with exceptions or so-called outliers as ancillaries….[which] is like focusing on the grass and missing out on the gigantic trees," he writes.

When it comes to the climate, which already is expected to warm a huge 3 degrees F in the next-twenty five years, this can’t be ruled out. And last month two researchers took a second look at the math of climate sensitiviity–the rising temperatures in years to come that we will experience due to the increased energy already stored in the oceans and the atmosphere. When we have doubled the usual rate of CO2 in the atmosphere, what will we see in terms of global temperatures?

This is a huge question for the IPCC; this year’s Fourth Assessment devotes pages 64-68 to introducing the discussion, and argues that in fact a central advance in this report is the increased precision we can place on the question of how quickly the planet will warm.

Where the last report estimated between 1.5 degrees Centigrade and 4.5 degrees C, the Fourth Assessment, which compares the performance of thirty different climatemodels against various sets of observations, much more confidently projects temperatures between 2 degrees C and 4.5 degrees C, mostly likely on the short side of 3. It admits that "Values higher than 4.5 degrees C cannot be excluded, but agreement with observations is not as good…"

Last month in the most prestigious of American science publications, Science, a study subtly challenged the IPCC on the likelyhood of a moderate sensitivity to increasing greenhouse gas permeation. Gerard  Roe and Marcia Baker took a second crack at the math and concluded that "the probability of large temperature increases are relatively insensitive to decreases in uncertainties associated with the underlying climate processes."

In other words, although we can exclude the possibility that the climate will not warm, the IPCC’s narrowing of the range of sensitivity was not warranted.

For a sympathetic analysis of their argument, you can consult the Three-Toed Sloth (who also usefully includes a link to the complete study). James Annan has doubts; mostly he objects that yes, the possibility of a huge increase cannot be completely rejected, but the IPCC has in fact considered it and concluded that almost certainly it will not happen. RealClimate tends to agree, a little less confidently, but splits the difference by pointing out that we can rule out negligible warming of no consequence, we must "recognize and confront" the possibility of unexpectedly high temps.

But what sticks with me is the comparison of a Gaussian set of possibilities [top diagram] with the long tail of an "outlier" [bottom diagram]. Looks kinda like a black swan…

Gaussiangaindistribution

Stochasticdistribution

  (h/p: Political Animal)

2 thoughts on “Black Swan Sighted in Climate Sensitivity

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