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Geoengineering wars: Another scientist teases out a surprising effect of global deforestation


AUSTIN—A new and unpublished analysis of the regional impacts of a hypothetical scheme to mitigate global warming via radical deforestation was unveiled here Sunday at a gathering of science journalists and writers, on the heels of a blogging firestorm about geoengineering and climate change in anticipation of the release of Superfreakonomics: Global Cooling, Patriotic Prostitutes, and Why Suicide Bombers Should Buy Life Insurance.

The book, due out October 20, is the follow-on book by University of Chicago economist Steven D. Levitt and New York Times journalist Stephen J. Dubner, authors of the 2005 bestseller Freakonomics: A Rogue Economist Explores the Hidden Side of Everything.

Related research on the impact of deforestation has previously been detailed by various scientists including Ken Caldeira of the Carnegie Institution of Washington's Department of Global Ecology in Stanford, Calif. In a 2007 paper in the Proceedings of the National Academy of Sciences, Caldeira used a 3-D climate model to mimic full global deforestation and found that by the year 2100, this approach would lower annual global mean temperatures by 0.5 degree Fahrenheit.

Taking the opposite tack, Caldeira had found in a 2005 paper in Geophysical Research Letters that replacement of all the Earth's vegetation by forests would result in a 1.3 degrees Celsius increase in mean global temperatures. Alternatively, global replacement with grasslands would result in cooling of 0.4 degree Celsius.

Now, Caldeira is featured, reportedly not in a flattering light, in Superfreakonomics, drawing the attention of blogger and climate expert Joseph Romm who calls the book "error-riddled" and accuses it, in this Climate Progress post, of promoting global cooling myths and sheer nonsense. (Dubner responded in this October 18 blog post, which refers to Romm's post as a "smear.")

Following up on the same geoengineering theme, Earth and atmospheric scientist Kevin Gurney of Purdue University offered similar details as Caldeira has found to attendees of the Council for the Advancement of Science Writing's annual meeting of his modeling of what would happen in three latitudinal zones if all Earth's trees were systematically stripped from land surfaces over time.

Like Caldeira, his modeling shows that at northern latitudes, the absence of trees would expose a lot of snow-covered surfaces that would reflect solar radiation away from Earth, resulting in global cooling in that region.

In the tropics, the opposite effect is found when all trees are stripped, according to Gurney's model. Removing trees amounts to removing the source of water in the atmosphere, which means no clouds would form there. Clouds reflect solar radiation away from Earth's surface, so eliminating them would result in global warming in the tropics. In that region, better results will come from efforts to slow down deforestation.

The deforestation results for Earth's mid-latitudes is "muddled" and "generally a good thing," Gurney said.

The results, currently under review at a scientific journal, have difficult policy implications, Gurney said, whereby the United States could decide to use deforestation as a global warming mitigation effort to its regional advantage at the expense of people living in the tropics and mid-latitudes.

"I'm not suggesting that countries are going to do this but it makes a problem that is hard even harder," Gurney said, adding that it could complicate negotiations for a consensus at the U.N. Climate Summit in Copenhagen in December. "No one's going to strip away all the trees, but there are strong incentives" domestically and elsewhere to engage in deforestation, he said.

An audience member asked Gurney if planting trees in northern latitudes would work to counter global warming, preventing the exposure of reflective snow. Gurney replied that there is not a lot of room in those latitudes to plant more trees "in a way that will cause a significant albedo effect," he said.

Gurney also detailed his Vulcan and Hestia projects that have modeled daily emissions of the primary climate-driving gas, carbon dioxide, as a result of the burning of fossil fuels, on fine space–time scales, potentially with a resolution of 25 meters. Vulcan focused on U.S. models for cities, whereas Hestia is going global. His "Breath of a Nation" video on YouTube illustrates the U.S. map in a 3-D animation and has been viewed more than 200,000 times.

The maps could be useful for local policy-setting, he said.



The views expressed are those of the author and are not necessarily those of Scientific American.

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