Science Sunday: Geoengineering, Parent Talk, Ice Loss
Sunday, August 19, 2007 at 7:00 am
Carbon geoengineering may cause drought
One potential method for dealing with global warming that’s developed some legs recently is geoengineering. These are often huge, Rube Goldberg ideas like huge sunshades in space to cool the planet, adding iron to the oceans to get it suck up more CO2, or mimicking volcanic activity by injecting sulfur into the stratosphere.
Large volcanic eruptions tend to cool the earth’s climate in a way that makes intuitive sense. The volcano spews dust and sulfur particles high into the stratosphere, where they are spread out and carried around the globe at high altitude. These particle reflect some of the incoming sunlight back into space. Less solar energy reaching the earth means that things cool down for a while, at least until the particles fall back to earth.But deliberately replicating volcanic activity to fight global warming might backfire, according to scientists Kevin Trenberth and Aiguo Dai of Boulder’s National Center for Atmospheric Research. They studied the 1991 eruption of Mt. Pinatubo in the Philippines. That eruption cooled the planet by a few tenths of degree for a couple of years.
However, according to Trenberth and Dai,
There was a substantial global decrease in precipitation over land, a record decrease in runoff and river discharge into the oceans, and widespread drying over land during the following year. Thus … major adverse effects, including drought, could arise from geoengineering solutions to global warming.
The research was published in this month’s issue of Geophysical Research Letters.
Talk to the parents
As Yogi Berra once said, you can observe a lot just by looking. Doctors from Denver’s Children’s Hospital and Yale School of Medicine found that applying this general principle to CT scans for children can result in better informed parents.
CT scans are “computerized tomography” that uses a computer and a series of x-rays to show cross-sectional images of internal body structures. Although CT scans only make up about 11 percent of radiologic procedures, radiation used in CT scans delivers about 70 percent of all the medical radiation dose to the U.S. population. Radiation, even in small doses, can contribute to an increased risk of cancer over a lifetime
I can hear you asking, what does this have to do with Yogi Berra? I’m coming to that. Children’s Hospital Dr. David B. Larson and colleagues found:
A brief informational handout can improve parental understanding of the potential increased risk of cancer related to pediatric CT without causing parents to refuse studies recommended by the referring physician.
In other words, parents make better decisions when they are more fully informed about the risks and benefits of the procedures proposed for their children.
The doctors gave 100 parents of children undergoing non-emergency CT scans a pamphlet describing radiation risk. Prior to reading the handout, only 13 percent knew that CT scans in crease the lifetime risk of cancer. After reading it, 86 percent knew. You can reliably count on 14 percent of Americans not to know anything, regardless of the subject matter.
Anyway, parents were then more willing to choose simple observation over a CT scan if that’s what the doctor recommended. But if the doctor recommended the CT scan, all the parents went along with the suggestion. “No parent refused or requested to defer CT after reading the handout.”
So it turns out you can learn a lot just by asking, too.
The paper also holds what I thought was a remarkable admission. They noted first, that “Patients also generally have a poor understanding of the radiation dose and risk associated with CT.”
Fair enough. But …
“While we were working on the handout, we found it extremely difficult to find meaningful estimates of exposure, dose, and risk for various types of procedures–even in the radiology literature. It is then not surprising that not only do parents underestimate the risk, but so do clinicians and radiologists,” Larson said. “When addressing the question of `how much does a CT increase the risk of cancer’ rather than providing a meaningful basis of comparison, most publications give one of two responses; either `the risk is slight’ or `it depends.’ While both may be accurate, neither are very helpful.”
So it sounds like not only do the patients have a poor understanding of the risks, so do the radiologists.
Dr. Larson explained it this way via email:
“Many estimates are available in the radiology and physics literature. These estimates are based on increased rates of cancer among atomic bomb survivors. Because of the unreliability of the data we have, the estimates have a high degree of uncertainty. In fact, it has not even been established with certainty that exposure to very low levels of radiation, such as CT, increases the risk of cancer at all. However, since we know that high levels of radiation increase the risk of cancer, we assume that low levels do as well, just to be on the safe side.
“What is lacking, though, is a body of literature that provides estimates of the risk associated with CT in a way that patients, and even most doctors, understand. Our study showed that if you tell patients about the increased risk of cancer associated with CT, parents do not become upset or refuse the study, as some physicians fear. We think it is appropriate to have an open discussion about these risks, both with individual patients and with the general public.”
The study appears in the August issue of the American Journal of Roentgenology.
How low can you go?
As of August 17, sea ice in the Arctic set a new record for its least extent, according to the National Snow and Ice Data Center in Boulder.
The center says:
Satellite measurements recorded the previous record, 5.32 million square kilometers (2.05 million square miles), on September 20-21, 2005. As of this morning, the extent was 5.26 million square kilometers (2.02 million square miles).
Sea ice extent is particularly low in the East Siberian side of the Arctic (the Chukchi and East Siberian Seas) and the Beaufort Sea north of Alaska. Ice in the Canadian Archipelago is also quite low. Along the Atlantic side of the Arctic Ocean, sea ice extent is not as strikingly low, but is still less than normal.
The Arctic is predicted to see the greatest temperature increases as a result of global warming.