A study by the National Academy of Sciences calls for experiments that would test technologies designed to counteract the global warming caused by greenhouse-gas emissions—a remarkable development for a field that even a decade ago was on the extreme fringes of science.
The study, sponsored by the U.S. National Research Council, the Central Intelligence Agency, NASA, and the Department of Energy, notes that geoengineering would only partially offset changes caused by greenhouse gases, and that it could introduce new problems of its own.
However, it is the first time a major report sponsored by the U.S. government has called for geoengineering experiments. Many have worried that even talking about geoengineering, let alone conducting experiments, distracts attention from efforts to reduce carbon dioxide emissions.
The report “says we won’t know if it’s a good solution until we’ve done more research,” says Lynn Russell, a professor of atmospheric chemistry at the University of California at San Diego and a member of the study committee. “Previous reports have not been willing to say that.”
The term “geoengineering” has been used to refer to a variety of ideas, such as decreasing atmospheric carbon dioxide by planting trees or deploying spacecraft as a vast solar umbrella. But two types of geoengineering have emerged as the most promising. One is injecting sulfur-based molecules into the upper atmosphere, where they would form particles that reflect sunlight into space. The other is spraying particles from ships or similar platforms to produce low-level clouds that perform the same function.
In an introduction to the report, Marcia McNutt, chair of the study committee and editor in chief of the journal Science, says the ease of using these technologies raises some concerns because no one understands what the effects might be. But despite these concerns, inaction on controlling greenhouse-gas emissions makes it ever more likely that some form of climate intervention will be considered.
The report says that geoengineering is no substitute for reducing emissions. It also says it would be “irrational and irresponsible” to start deploying geoengineering technologies at a large scale. It calls for small-scale experiments that could clarify what would actually happen if they were deployed at a larger scale.
The report doesn’t recommend specific experiments, but it notes that studies might shed light on the chemistry and physics of cloud formation and the interaction of sulfur-based particles with the ozone layer. It also suggests starting with experiments that researchers would want to do anyway to improve their climate models.
Even small-scale experiments would be controversial. And there are some doubts that such experiments would reveal the ramifications of deploying geoengineering at a scale large enough to actually cool off the planet.
In addition to calling for research, the report also emphasizes the need to come up with international rules for geoengineering.
David Victor, an expert on climate policy from the University of California at San Diego, says it would be best to start the research and develop policies along the way. At this point, Victor says, too little is known for a serious discussion to begin. “No one would know what they were negotiating,” he says.
Alan Robock, a professor of environmental sciences at Rutgers University who has raised questions about geoengineering in the past, says that small-scale experiments would be permissible as long as an independent governing body was created to evaluate their environmental impact. “We can’t just trust the scientists,” he says. He adds, however, that the experiments would have limited use: “You can test specific mechanism and processes, but you can’t test the global impact without actually doing geoengineering.”
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