Long ago the Tusk noted a fascinating 2010 missive from The Bos concerning the virtue of everyone (else) remaining intellectually flexible. Or, as he put it, having a willingness to “change your mind.” Here is the link and I have copied the text at the bottom.

The Bos’ statement has not aged well. I attended his 2009 AGU Session and I shared his admiration of Wally Broecker’s willingness to change his mind regarding YD initiation via a St. Lawrence floodway. It was kinda of neat to be there in person when a major theory took a turn with the driver at the wheel. In retrospect, though, I doubt The Bos would make his current appeal using Broecker as his example.

Here is The Bos’ concluding remark where he recommends Broecker to the YDB team as an example of a nimble intellect following the data wherever it may lead:

The Younger Dryas impact proponents would do well to follow his example.

When Scientists Actually Change Their Minds, Mark Boslough, Skeptical Inquirer, May / June 2010

And here is Broecker himself this year concerning the Younger Dryas impact in NatGeo:

“Most people were trying to disprove this,” said Wallace Broecker, a geochemist and climate scientist at Columbia University’s Lamont-Doherty Earth Observatory. “Now they’re going to have to realize there’s some truth to it”.

Did a Comet Really Kill the Mammoths 12,900 years Ago?, National Geographic online, September 10, 2013

So, The Bos makes a sanctimonious appeal to actively publishing research scientists to change their minds and drop their theory, using as his exemplar a scientific authority who later re-considers his own previously critical opinion of the same theory —  a theory to which The Bos himself remains implacably opposed?! How rich!

Perhaps The Bos should take his own advice in the New Year, personally follow Broecker’s example, and carefully re-consider the YDB impact as a legitimate subject deserving further study.

As a graduate student in 1980, I was interested in impact cratering. I had just finished reading the comet catastrophe novel Lucifer’s Hammer when Luis Alvarez, the famous physicist from Lawrence Berkeley, came to Caltech to present a colloquium on his group’s asteroid hypothesis. It made so much sense. What else but an impact could possibly cause a global climate catastrophe and mass extinction?

Many years later, I read an article that featured Wallace Broecker, the Columbia University scientist with revolutionary ideas about catastrophic climate change caused by abrupt slowdowns in ocean circulation. I was fascinated by his idea that the rapid onset of the Younger Dryas cold spell could have been caused by the collapse of an ice dam and a deluge of freshwater into the North Atlantic that shut off the Gulf Stream, stopping the flow of tropical heat to the northern continents and plunging them into ice-age conditions. He showed that there could be other causes of global catastrophes that don’t involve impacts.

I was delighted when Broecker agreed to give the opening presentation at the American Geophysical Union (AGU) session I helped organize, but I was surprised to learn that he had abandoned his famous hypothesis about the cause of the Younger Dryas. He started his presentation by reminding everyone that he used to argue that it was triggered by the flood from the ice-age Lake Agassiz, but when he flew over the route the floodwaters should have followed, he saw no geomorphic evidence for a flood. He had changed his mind!

His primary objections to the impact hypothesis were the same as his objections to the flood he had previously championed as the explanation: lack of evidence and lack of uniqueness of the Younger Dryas. Abrupt changes in climate, both warming and cooling, have happened many times, and Broecker argues that the climate system is inherently unstable. Why should only one of a long sequence of changes have such an improbable and catastrophic trigger event—whether impact or flood—when the climate system has repeatedly undergone such changes all by itself?

In his 1987 CSICOP address, Carl Sagan said, “In science it often happens that scientists say, ‘You know that’s a really good argument; my position is mistaken,’ and then they actually change their minds and you never hear that old view from them again… . I cannot recall the last time something like that has happened in politics or religion.”

Broecker’s esteem among scientists was not diminished when he changed his mind. The Younger Dryas impact proponents would do well to follow his example.

Mark Boslough was co-organizer of the AGU Younger Dryas session in December. He is a physicist at Sandia National Laboratories and an adjunct professor at the University of New Mexico.

Mark Boslough

Mark Boslough is a physicist at Sandia National Laboratories and adjunct professor at the University of New Mexico. His work on comet and asteroid impacts has been the subject of many recent TV documentaries and magazine articles. He believes that the impact risk—at its core—is primarily a climate-change risk, and he has turned his attention to climate change as a looming national security threat. The opinions expressed here are his own.