In “How Much Do CT Scans Increase the Risk of Cancer?” Carina Storrs accurately discusses the reasons diagnostic imaging with computed tomography scans has increased and the limited scientific knowledge of the effects of this increased radiation exposure on inducing cancer in patients. As a radiologist, I find that Storrs neglects to include one cause for the increase in CT scans: the current structure for how these exams are ordered in the U.S. health care system.

In the U.S., practicing physicians order diagnostic studies that they believe are appropriate. Radiologists, who are the experts in the advantages and disadvantages of different imaging modalities and are the ones that interpret the studies, have no ability to either reject or change the requested study without permission from the ordering physician. Consequently, a certain amount of nonoptimal and unneeded exams will be ordered.

This generally occurs because of lack of communication with the ordering physician to optimize the diagnostic test (the American College of Radiology has developed appropriateness criteria for diagnostic studies to address this issue). Sadly, it also occurs because in the current U.S. reimbursement structure, there is no financial incentive to cancel a nonindicated or nonoptimized study.

Benjamin L. Viglianti
Department of Radiology
University of Michigan


In “Oil Sands May Irrevocably Tar the Climate,” David Biello reports on efforts to halt the Keystone XL pipeline. By allowing for increased heavy oil production in the Alberta tar sands, the pipeline would accelerate the buildup to the cumulative carbon-emissions threshold of one trillion metric tons, at which we will reach the feared “tipping point” of more than two degrees Celsius of warming. The article points out that emissions must drop by 2.5 percent a year, starting now, for us not to exceed that threshold by 2041. Such an annual reduction would mean cutting energy use from carbon in half in about 30 years. One possible way to get there is by cutting world economic output in half. No one will willingly do that. At least not until economic collapse occurs following runaway atmospheric heating.

Incredible innovation and cooperation among nations are required. That will happen only when the majority of the powerful people of the wealthy nations realize they breathe the same air as the weak and the poor. The history of human behavior makes that outcome seem most unlikely.

Tom Faulkner
via e-mail

For 40 years I have watched environmentalists block hydroelectric power, nuclear power, offshore oil drilling, continental gas drilling and wind power projects. This focus on “purity of purpose” rather than “consequences of actions” resulted in utilities building dozens of heavily polluting coal plants and oil companies investing billions of dollars in Canadian tar sands.

The recent breakthroughs in fracking have reduced carbon emissions as utilities have begun to switch from coal to now dramatically cheaper natural gas. The potential use of natural gas in vehicles will reduce emissions even more. Unfortunately, since fracking doesn't meet the zealots' agenda, these significant environmental benefits are being strongly opposed.

Robert Gallant
Midland, Mich.

There is one major omission with regard to alternatives if Keystone fails: the energy-transport company Enbridge. While all attention has been on Keystone, Enbridge has been quietly building its own tar sands network to the Gulf and East coasts.

commenting at www.ScientificAmerican.com


In “Blind Kids Gain Vision Late in Childhood While Giving a Lesson in Brain Science,” Pawan Sinha describes his work in surgically curing cataract-caused blindness in children in India.

Sinha's comments on “intermodal organization”—in which information received through the eyes is correlated with that received through the other senses—reminded me of Annie Dillard recounting the story of the first successful cataract operations in Europe in her 1974 nonfiction narrative Pilgrim at Tinker Creek. Quoting an English translation of the 1932 book Space and Sight, she wrote: “Before the operation a doctor would give a blind patient a cube and a sphere; the patient would tongue it or feel it with his hands, and name it correctly. After the operation the doctor would show the same objects to the patient without letting him touch them; now he had no clue whatsoever what he was seeing. One patient called lemonade ‘square' because it pricked on his tongue as a square shape pricked on the touch of his hands.”

Bill Peak
Easton, Md.


When Animals Mourn,” by Barbara King, discusses evidence of nonhuman mourning, including in cats.

Our cats, Simba and Nala, were littermates and for 14 years were never more than a few feet from each other. Nineteen months ago Simba had to be put down.

Nala immediately began to have spells of howling every day. She goes from room to room, calling in each. The raw anguish in her tone is unmistakable.

If she perceives a threat, she claws frantically at the bed coverlet where Simba would burrow for his naps. I often lie in bed reading my current magazine, which I rest on my raised knees: the two of them would crawl under my knees and cuddle there. Nala now checks into that empty space, emits one of her anguished howls, leaves and glares accusingly at me.

It is dangerous to draw conclusions from anecdotes, but Nala richly meets the criteria for grief given in the article. She is, unmistakably, mourning for her brother.

Frank Gue
Burlington, Ontario


People Kill with Guns More Than Any Other Weapon,” by Mark Fischetti [Graphic Science], illustrates statistics that show that in the U.S., guns are used more than other weapons in killings and that people are most often killed with them by others whom they know.

I would like two things to address gun violence: 1) Better education required for gun owners on how to effectively store and operate their firearm and on when it is appropriate to use it. 2) Better requirements and solutions for the safe storage and possession of a firearm.

I'm not talking about a full ban but about making it a requirement that those who own a firearm have a full and working understanding of it and its consequences.

commenting at www.ScientificAmerican.com


James Cameron Donates His Tricked Out Ocean Sub to Science,” by Larry Greenemeier [Advances], refers to James Cameron performing the first manned mission to the Pacific Ocean's Challenger Deep site in DEEPSEA CHALLENGER. It should have stated that his was the first solo manned mission.

In “Walls of Water Make Chaotic Currents More Predictable,” by Dana Mackenzie, George Haller's affiliation was outdated; he is at the Swiss Federal Institute of Technology Zurich.