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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Transcript

RACHEL MARTIN, HOST:

The scientific consensus is that the Earth is warming, and some climate experts wonder if we might reach a point when we need to do something to try to cool the planet, something drastic, like creating artificial clouds to reflect sunlight back into space. Talking about this kind of thing used to be almost taboo among scientists. NPR's Nell Greenfieldboyce reports that's not only changing, some of the nation's top researchers say they are options we can no longer afford to ignore.

NELL GREENFIELDBOYCE, BYLINE: Not too far from the White House is the historic National Academy of Sciences Building. It's got a big statue of Albert Einstein out front, and it is the home of the country's scientific establishment. So it was a little jarring to hear folks here talking about deliberately messing with the planet's thermostat. This is sometimes called climate geoengineering.

MARCIA MCNUTT: All of us are mostly pretty scared of geoengineering.

GREENFIELDBOYCE: Marcia McNutt is a geophysicist and editor-in-chief of Science, the influential research journal. Despite her fear, she agreed to chair a committee that looked into this. Given that the world isn't doing much to limit the greenhouse gas emissions that cause climate change, she felt like she had to.

MCNUTT: It is prudent to ask ourselves what is the science behind climate intervention strategies.

GREENFIELDBOYCE: Reporters and researchers gathered today as her committee released two new reports about that science. One report looks at the possibility of quickly cooling the planet by sending sunlight back into space. This could be done by having airplanes release sulfuric acid in the stratosphere, creating aerosols that reflects sunlight. The report says this approach would be doable with today's technology. Still it would be incredibly risky with unknown effects on the ozone layer and global precipitation. The committee said don't do it now, but it is something we need to research further and understand.

MCNUTT: There would need to be a lot of work before we would know whether the risks could be reduced.

GREENFIELDBOYCE: The second report looks at a less controversial approach - sucking carbon dioxide out of the air. McNutt says this would be slow and expensive, but it's not dangerous. Direct-capture technologies are still in their infancy, but there are tried-and-true measures, like planting forests

MCNUTT: We should be doing that - better land-use management - we should be doing that - duh. These are absolutely things that we should be pursuing.

GREENFIELDBOYCE: But spewing sulfuric acid into the atmosphere - you're not so down with that.

MCNUTT: I'm not down with that. I hope we never get to that point and I think we need to know exactly what the ramifications are before someone does it to us or before someone thinks it would be a good idea.

GREENFIELDBOYCE: Now, scientists are always calling for more research. But this time it really is a big deal because this is such a prestigious government advisory group, and this is such a contentious area of science. David Keith is a climate science researcher at Harvard University.

DAVID KEITH: What I hope it will do is give government officials an excuse to move.

GREENFIELDBOYCE: He says there's been a reluctance to fund research on climate fixes. He thinks officials worry that even just talking about this could undermine the sense of urgency about cutting greenhouse gas emissions.

KEITH: That is the underlying fear, separate from all the science, that really is the thing that makes people squeamish.

GREENFIELDBOYCE: Despite these concerns, scientists say they need to understand the risks and benefits of what kind of things could be done if only because someday other nations might want to do something. The initial funder for this scientific review was the U.S. Intelligence Community. Alan Robock is a climate scientist at Rutgers University. He says there's the potential for real conflict.

ALAN ROBOCK: If you could do it, what temperature would you like to set the planet's thermostat to, and who controls that thermostat?

GREENFIELDBOYCE: Countries might decide to act unilaterally. There might be disagreements. Robock says there's an international agreement not to modify the environment for hostile purposes, but who decides what's hostile?

ROBOCK: If you say I'm doing it because I want the planet to be cooler and I don't want my sea level to rise, and somebody else says yeah, but you're affecting the frequency of droughts in my country - is it hostile or not?

GREENFIELDBOYCE: That's not a question science can answer. But that kind of scenario is why scientists say they need to start learning more about climate interventions now. Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright NPR.

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