Steve Carpenter on Black Swans

Ecologist Steve Carpenter follows up on Don Ludwig’s comments on Nassim Nicholas Taleb‘s book The Black Swan:

Both of Taleb’s books are highly entertaining. But he over-reaches. There are some odd mistakes. For example, he makes much of a supposed kink in the integral of the Student-t distribution, (where tail probability declines linearly with deviation from the mean) but if you compute the integral using R software there is no kink — so Taleb evidently made a mistake.

Based on web sites, Taleb made his fortune using a kind of option trade. He purchases only options to buy securities at a certain price during a specified time window in the future. So if the security is trading above Taleb’s price, he buys it and then immediately sells at the market price, thereby making a profit. He says that his life involves long periods of time watching while nothing happens and his options to buy expire. But once in a great while he makes a killing. This is exactly like predators who specialize on very large prey, or fishing for big game fish, or hunting for rare but big game animals.

His writings have done a lot to publicize the importance of huge rare events. I think this is a good thing. But also he over-reaches. In some recent interviews he seems to be gloating over the current economic collapse. And (according to economist colleagues) some economists see his ideas as rather routine. Yet he is a provocative and entertaining writer; if sales measure impact he has made a difference.

To me, the most novel feature of the current ongoing collapse is the coincidence of huge shocks with apparently different triggers. Who would have thought that an epidemic of bad loans in America, steep ramp of energy prices, and biofuels tightening the link of energy to food prices would coincide, against a backdrop of lower economic firewalls between countries and increasingly intense food limitation of the human population, with almost no scope for growth of the food supply. It’s a wonderland for testing resilience ideas and a global tragedy, all at the same time.

For a recent talk I re-analyzed a bunch of information from the Millennium Assessment, to try to figure out if humanity had any chance at all for making it through the next few decades.

If everyone shifts trophic status to roughly herbivore level, and we educate all the world’s women to secondary level, we have a chance.

The difference between 12 billion and 9 billion people in 2050 is one child per woman. If all the world’s women were educated to secondary level, fertility would drop by about 1.7 children per woman. And we can probably feed 9 billion herbivorous people, if we can maintain the crop diversity of the major grain crops high enough to avoid catastrophic disease outbreaks.

Energy needs for agriculture and climate change could make it pretty hard to achieve the rosy scenario; climate heating, more variable precipitation and sea level rise have bad implications for agriculture. So the rosy scenario itself may be way out on the tail of the distribution. And what will happen to relations among people as the going gets rough? Human conflict can wreck agriculture. What are the chances that no one will use nuclear weapons? Even a few nukes would take out huge areas of arable land for millennia. And, as Will Rogers said about land, they ain’t makin’ any more of it. A Taleb-like fat tail breakdown seems not so implausible.

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