# 'What the Earth Knows': an exchange.

 Position: LETTERS - Letter to the editor

FREE EXCERPT

In the Summer 2010 issue of the SCHOLAR, we published as our cover story an article by Robert B. Laughlin, a Nobel laureate physicist at Stanford University, suggesting that a greater understanding of geologic time gives a new perspective on climate change and our future energy needs. The article drew lots of commentary, ranging from a column by George F. Will in Newsweek to postings from the far reaches of the blogosphere. Joel E. Cohen of the Laboratory of Populations at Rockefeller and Columbia universities, an occasional contributor to the SCHOLAR, submitted the following critique, to which Professor Laughlin responds.

Dear Professor Laughlin:

Thank you for your efforts to communicate complex scientific information to the general public through "What the Earth Knows." However, I am startled by the arithmetic errors in your article, and even more by errors of fact and logic.

Arithmetic error 1: "This rate appears to the eye of a regular visitor to be about one millimeter per year, perhaps less, for the rock here is relatively hard, so that it would take 100,000 years to erode a kilometer, or about a million years to erode away the shore entirely."

A kilometer is 1,000 meters, and each meter has 1,000 millimeters. At one millimeter per year, it would take 1,000 x 1,000 = a million years to erode a kilometer, not 100,000 years. If the rate of erosion were less than one millimeter per year, it would take more than a million years to erode a kilometer.

Arithmetic error 2: "It's also consistent with estimates of the ice mass required to leave behind such industrial-strength mischief as Long Island, Nantucket, and the Great Lakes--about 50 million cubic kilometers in all, or five million billion tons."

A cubic kilometer contains 10^9 (= 1 billion) cubic meters. A cubic meter of water weighs 1 metric tonne. Therefore 50 million cubic kilometers of water weigh 50 million billion metric tonnes. Ice, at its least dense, weighs about 0.92 grams per milliliter, or about 0.92 metric tonnes per cubic meter, or about 0.92 billion metric tonnes per cubic kilometer. Fifty million cubic kilometers of ice would weigh nearly 50 million billion American tons, or about 10 times more than five million billion tons.

I have not checked the rest of your arithmetic.

Error of fact and logic 1: "... keeping carbon-based fuels in the ground a while longer won't make much difference in mitigating the loss of biodiversity. The real problem is human population pressure generally-overharvesting, habitat destruction, pesticide abuse, species invasion, and so forth. Slowing man-made extinctions in a meaningful way would require drastically reducing the world's human population. That is unlikely to happen."

You ignore the extinction risks of drilling, mining, spills, leaks, toxic dumps, and habitat fragmentation associated with fossil-fuel extraction, transport, and use. Then you make a heroic, and faulty, leap in logic. "Overharvesting, habitat destruction, pesticide abuse, [and] species invasion," which are real causes of species extinctions, are at most weakly coupled to human numbers and spatial distribution, but are strongly coupled to technological, economic, legal, and political factors that can be influenced independently...