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Today the White House released a report that reminds us that global warming is already affecting our weather and it's going to get worse. The report says cutting carbon dioxide emissions is a necessary step. Meantime, the National Academy of Sciences held a meeting this week to look at some of the more far out ideas. Those ideas focus on whether we could safely cool the planet by engineering the climate.

NPR's Richard Harris went to the meeting to find out more.

RICHARD HARRIS: It seems like science fiction - manipulating our atmosphere to counteract the effect of all the heat-trapping carbon dioxide that we're pumping into the air. That's certainly what earth scientist Ken Caldeira thought a decade ago when he first heard this subject raised in a talk by a nuclear weapons researcher.

Dr. KEN CALDEIRA (Earth Scientist): He basically said we don't have to bother with emissions reduction, we can just throw aerosols - little dust particles in the stratosphere, and then that would cool the earth. And I thought, oh, that'll never work.

HARRIS: Caldeira sat down to study this and was surprised to discover, yes, it would work - for the very same reasons that big volcanoes cool the earth when they erupt. Fine particles in the stratosphere reflect sunlight back into space - and it would be cheap to do.

Caldeira is at Stanford and the Carnegie Institution. He says, over the past decade, talk about this idea has moved from cocktail parties to very sober meetings, like the one this week put on by the National Academy of Sciences.

Dr. CALDEIRA: Frankly, I'm a little ambivalent about all this - that I've been pushing very hard for a research program, but it's a little scary to me as it becomes more of a reality to think that we might actually start learning how to toy with our environment, or our whole climate system at a planetary scale.

HARRIS: This raises so many questions, like, when would you even consider trying it? Caldeira argues we should have the technology at the ready in case there's a climate crisis: collapsing ice sheets, famine, something of that nature.

At the academy's meeting, Dan Schrag from Harvard University agreed with that — up to a point.

Dr. DAN SCHRAG (Harvard University): I think we should consider climate engineering only as an emergency response to a climate crisis, but I question whether we're already experiencing a climate crisis — whether, in fact, we have already crossed that threshold.

HARRIS: The reality is carbon-dioxide emissions globally are on a runaway pace, despite rhetoric promising to control them. David Keith, from the University of Calgary, suggested we should consider moving toward experiments that would test ideas on a global scale sooner rather than later.

Dr. DAVID KEITH (University of Calgary): It's not clear that during some supposed climate emergency would be the right time to try this new and unexplored technique.

HARRIS: Experiments could create disasters. During a coffee break, Alan Robock at Rutgers University cataloged a long list of risks. Particles in the stratosphere that block sunlight could also damage the ozone layer, which protects us from harsh ultraviolet light.

Dr. ALAN ROBOCK (Rutgers University): Or that it would reduce precipitation in Asia, where it's a source for food for two billion people.

HARRIS: Imagine if we triggered a drought and famine while trying to cool the planet. On the plus side, it's also possible that diffusing sunlight could end up boosting agriculture, he said.

Dr. ROBOCK: We need to evaluate all these different, contrasting impacts to see whether it really would have an effect on food or not. Maybe it's a small effect. We really don't know that yet. We need more research on that.

HARRIS: Thought experiments to date have focused primarily on the risks of putting sulfur dust in the stratosphere. But there are lots of other geoengineering ideas — like making clouds brighter by spraying seawater particles into the air.

Social scientist Susanne Moser says even the simplest ideas aren't simple at all.

Dr. SUSANNE MOSER (Social Scientist): I don't think that there is a quick and easy answer to employing even one of those quick and cheap and easy solutions.

HARRIS: There's no mechanism in place to reach a global consensus about doing this — and a consensus seems unlikely in any event. Who gets to decide where to set the global thermostat? And will this simply become an excuse not to control our emissions to begin with? These were all questions without answers at the academy's meeting.

Richard Harris, NPR News.

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