Before anyone tries to cool the Earth with technologies that could counteract global warming, there needs to be a lot more research into the benefits and risks. That's the conclusion announced Tuesday by a scientific panel convened by the prestigious National Research Council to assess "climate geoengineering" — deliberate attempts to alter the global climate.

Geoengineering has been seen as the potential last-ditch option to stave off the worst effects of climate change, given that agreements to reduce greenhouse gas emissions have been slow in coming.

The basic idea is simple: Either suck carbon dioxide from the atmosphere or reflect incoming sunlight away from Earth.

But the prospect of intentionally mucking with the world's climate is hugely controversial. Until recently, even discussing it has been somewhat taboo among scientists. One fear is that nations might fight to control the global thermostat — unilaterally taking action to try to adjust temperatures to their liking.

Another is that the promise of a quick geoengineering fix would discourage the world from doing the hard work needed to actually reduce greenhouse gas emissions.

So several agencies of the U. S. government — including the intelligence community — and the National Academy of Sciences asked an independent committee to assess the state of the art and weigh in.

The committee found that more conventional approaches to removing carbon dioxide, such as reforestation, are low-risk and well-understood but costly and slow. And new technologies designed to directly capture carbon dioxide are immature, the panel said.

Meanwhile, taking steps to reflect more sunlight back into space could work to cool the planet quickly, much as volcanic eruptions have in the past. And it wouldn't take too much money or technological innovation to simply inject aerosols into the stratosphere or brighten marine clouds.

But the risks could be huge. Aside from the threat of damage to Earth's ozone layer, and unknown consequences for global precipitation patterns, there could be political fallout and social upheaval.

The committee recommended against attempting this, but said research was needed to better understand it. And some experts on climate science welcomed that stance.

"I think we have to know. I think we have to know what the risks are and what the benefits might be so we can make informed decisions in the future," says Alan Robock, a climate scientist at Rutgers University who was not on the committee. "Would it be more dangerous to do it or to not do it? That's the question."

Being in favor of research into geoengineering is not the same as being in favor of geoengineering, Robock says. And everyone calling for this research, he says, knows that nothing can replace the need for real action on reducing emissions.

"All of us understand that global warming is real, it's being caused by humans, and it's going to have bad consequences on the average," says Robock. "And so we're all in favor of mitigation [and in] not putting carbon dioxide and other greenhouse gases into the atmosphere in the first place."

David Keith, a climate science expert at Harvard University, points out that other nations have already set up dedicated research programs to look at geoengineering; the U.S. has lagged behind.

"I hope this time the government listens and actually gets over its fears — in some ways healthy fears — and authorizes a real, broad research program," Keith says. "Right now, if you talk with senior people in Washington, D.C., in the science-funding community, there are many people who, behind a closed door, will say, 'Yeah, we'd really like to fund some work on solar geoengineering but we're afraid of all the flak we'll get if we do it.' "

Keith has one proposal to put a minuscule amount of sulfate particles into the atmosphere, as a test of the effect on ozone and whether that effect could be managed.

"Whether or not you think it's a useful idea, it's incredibly small, in terms of an environmental impact," he says, noting that the pollution released would be the equivalent of a minute or so of a commercial airline flight.

"The central, biggest fear is the fear that just even talking about this, or researching it and popularizing it, will lessen the strength of our commitment to cut emissions," says Keith. "That is the underlying fear — separate from all the science — that really is the thing that makes people squeamish."

That, and the idea that some nation might take matters into its own hands and start messing with the planet.

Keith notes that although the intelligence community has a legitimate interest in trying to understand long-term risks to national security, he doesn't think it's a good idea for the intelligence community to be seen as a major sponsor of this scientific assessment.

"Because the main thing that's so important," he says, "is that we have this be transparent technology, and that we attempt to build international cooperation from the beginning."

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