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might object to cooling the earth, especially if higher temperatures have brought them advantages such as longer growing seasons and milder winters. And if geoengineering decreases rainfall, countries that have experienced droughts due to global warming could suffer even more.

No current international laws or agreements would clearly prevent a country from unilaterally starting a geoengineering project. And too little is known now for a governing body such as the United Nations to establish sound regulations–regulations that might in any case be ignored by a country set on trying to save itself from a climate disaster. Victor says the best hope is for leading scientists around the world to collaborate on establishing as clearly as possible what dangers could be involved in geoengineering and how, if at all, it might be used. Through open international research, he says, we can “increase the odds–not to 100 percent–that responsible norms would emerge.”

Ready or Not

In 2006, Paul Crutzen, the Dutch scientist who won the Nobel Prize in chemistry for his discoveries about the depletion of the stratospheric ozone layer, wrote an essay in the journal Climatic Change in which he declared that efforts to reduce greenhouse-gas emissions “have been grossly unsuccessful.” He called for increased research into the “feasibility and environmental consequences of climate engineering,” even though he acknowledged that injecting sulfates into the stratosphere could damage the ozone layer and cause large, unpredictable side effects. Despite these dangers, he said, climatic engineering could ultimately be “the only option available to rapidly reduce temperature rises.”

At the time, Crutzen’s essay was controversial, and many scientists called it irresponsible. But since then it has served to bring geoengineering into the open, says David Keith, who started studying the subject in 1989. After a scientist of Crutzen’s credentials, who understood the stratosphere as well as anyone, came out in favor of studying sulfate injection as a way to cool the earth, many other scientists were willing to start talking about it.

Among the most recent converts is David Battisti, a professor of atmospheric sciences at the University of Washington. One problem in particular worries him. Studies of heat waves show that crop yields drop off sharply when temperatures rise 3 °C to 4 °C above normal–the temperatures that MIT’s Prinn predicts we might reach even with strict emissions controls. Speaking at ageoengineering symposium at MIT this fall, Battisti said, “By the end of the century, just due to temperature alone, we’re looking at a 30 to 40 percent reduction in [crop] yields, while in the next 50 years demand for food is expected to more than double.”

Battisti is well aware of the uncertainties that surround geoengineering. According to research he’s conducted recently, the first computer models that tried to show how shading the earth would affect climate were off by 2 °C to 3 °C in predictions of regional temperature change and by as much as 40 percent in predictions of regional rainfall. But with a billion people already malnourished, and billions more who could go hungry if global warming disrupts agriculture, Battisti has reluctantly conceded that we may need to consider “a climate-engineering patch.” Better data and better models will help clarify the effects of geoengineering. “Give us 30 or 40 years and we’ll be there,” he said at the MIT symposium. “But in 30 to 40 years, at the level we’re increasing CO2, we’re going to need this, whether we’re ready or not.”


Kevin Bullis is Technology Review’s Energy Editor.

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Videos by Kevin Bullis, edited by Brittany Sauser

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