## The Atlantic Monthly Death Spiral Watch (Gregg Easterbrook Asteroid Devastation Edition)

Why oh why can't we have a better press corps? The Atlantic Monthly features Gregg Easterbook, who writes:

The Sky Is Falling: The odds that a potentially devastating space rock will hit Earth this century may be as high as one in 10. So why isn’t NASA trying harder to prevent catastrophe?

If the odds that a devastating space rock will hit the earth in a century are one in ten, then the chances that we have gone...

• one millennium without a DSR hitting the earth are 0.35...
• two millennia without a DSR hitting the earth are 0.12...
• four millennia without a DSR hitting the earth are 0.014...

It's possible a devastating space rock hit the earth between eight and four millennia ago and we know nothing about it--but it's not terribly likely. It's very hard for me to believe that a devastating space rock has hit the earth since 3000 BC. We have Tunguska--and that's pretty much it[1].

That means that if you started out with a 50-50 prior probability that Gregg Easterbrook knows what he is talking about, your posterior probability that the lead of his Atlantic article is better than birdcage liner given no rock since 2000 BC is 0.0138. But we start with a lower probability than that, don't we? Gregg Easterbrook has a history, doesn't he? I would start with a prior probability that Easterbrook knows what he is talking about of one in a ten, in which case our posterior judgment, given no rock since 3000 BC, is 0.0014. If the Atlantic published an article by Gregg Easterbrook every month, we would have to wait 41 years before there was a 50-50 chance that even one of the Easterbrook articles was right.

"Odds that a potentially devastating space rock will hit Earth this century may be as high as one in 10." Feh!!

[1] Yes, I know that Easterbrook claims that the abnormally cold weather of 536-537 was caused by a dust cloud raised by a "space object about 300 meters in diameter hit[ting] the Gulf of Carpentaria, north of Australia, in 536 A.D." But I had thought that sulphur left in ice cores in 536-7 was strong evidence that the cause was a volcanic eruption: see http://www.realclimate.org/index.php/archives/2008/03/536-ad-and-all-that/. Easterbrook doesn't mention SO4 concentrations in ice cores.