X-rays stream off the sun showing observations from NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, overlaid on a picture taken by NASA’s Solar Dynamics Observatory. (AFP/NASA/JPL-Caltech)

The first thing to understand about geoengineering — intentional modification of the climate system to counter the effects of global warming — is that we shouldn’t even be having a conversation about geoengineering.

Just convening that conversation — which has gained a new megaphone, thanks to a report just released by an expert panel assembled by the National Research Council of the U.S. National Academy of Sciences — in a sense means that we’ve failed to reduce carbon dioxide emissions enough to prevent the risk of dangerous climate change. And thus, we’ve also failed to take geoengineering off the table.

The committee was chaired by Marcia McNutt, the editor-in-chief of Science and formerly the director of the U.S. Geological Survey, who said in a released statement, “That scientists are even considering technological interventions should be a wake-up call that we need to do more now to reduce emissions, which is the most effective, least risky way to combat climate change.”

The National Research Council recommends — very reluctantly, and only for purposes of increasing our knowledge — government-sponsored research into so-called albedo modification, sometimes also called solar radiation management (a term the committee preferred not to use).

Albedo” is a scientific term that refers to reflectivity — in this context, how much the Earth bounces light away and back to space. Thus albedo modification means altering reflectivity of the planet, for instance by injecting large volumes of sulfate particles into the middle atmosphere, so as to deflect sunlight away before it gets to us here at the surface, and thereby induce a global cooling.

In effect, this would be like installing an artificial thermostat to turn down the Earth’s dangerously rising temperature — last year was the hottest on record — by banishing some of the energy streaming to us from the sun. We know that it would work, researchers say, because we know that large volcanic eruptions cool down the planet by physically similar means.

Tens of millions of tons of sulfate aerosol, for instance, could offset a doubling of carbon dioxide in the atmosphere. But there would be unknown knock-on effects, ranging from changing global precipitation patterns to ozone depletion. And they would be unevenly distributed across the world, the panel noted, potentially sparking controversy over inequitable consequences, much as global warming itself does now.

Here’s a visualization of some possible strategies for albedo modification:


“They don’t want any deployment right now, but the fact that they think there’s a need to do the research, and get organized, to me is the most important thing,” says Rafe Pomerance, a former Clinton administration State Department official on environment and development and a current member of the National Academies’ Polar Research Board. “The issue is getting a lot more attention.”

The scientists make clear that they would consider any deployment of geoengineering techniques like albedo modification to be reckless, given inadequate knowledge of the downstream consequences. Indeed, they write, artificially changing the Earth’s reflectivity at all would be “irrational” without trying to cut down on carbon dioxide, as well. That is especially the case in that albedo modification is only a bandage that doesn’t make the underlying problem — carbon dioxide — go away. If you were to ever stop geoengineering after starting it, global warming would snap right back.

Nonetheless, the committee did recommend U.S. government-sponsored research on the matter to learn more about its “risks and benefits.” It pivoted toward doing so with a crucially hesitant sentence that bears parsing and rereading: “The Committee argues that, as a society, we have reached a point where the severity of the potential risks from climate change appears to outweigh the potential risks from the moral hazard associated with a suitably designed and governed research program.”

For a long time, even discussing geoengineering had been considered a “moral hazard” by some, because it could undermine actions to address the root causes of the problem — carbon dioxide emissions.

Overall, the report represents a “big tent” approach, notes Raymond Pierrehumbert, a geophysicist at the University of Chicago who served on the committee, suggesting a range of views among the participating scientists (there were 16 committee members).

“One of the best things that could come out of the NRC report is to just alert people to the fact that unrestrained emissions could make the world so bad that we might do something like albedo modification just out of desperation,” says Pierrehumbert.

Reasoning that there are many scenarios in which we would need to know more about artificially changing the Earth’s reflectivity — for instance, if a rogue state decides to try it — the committee recommended that the U.S. Global Change Research Program head up studies on the matter, and that the research be performed in such a way as to simultaneously increase our basic knowledge of the climate system.

The recommendation includes conducting “small-scale field experiments” with “controlled emissions” — provided it is clear that they are too localized and minuscule in scale to have any significant climatic effect. All of this would need to occur, notes the committee, under the aegis of a deliberative process about how to govern geoengineering research, to ensure ethical considerations are weighed and to balance risks and benefits.

The National Research Council report was sponsored by a number of U.S. science agencies and also the U.S. intelligence community. In a separate report, the National Research Council explored the subject of carbon dioxide removal, which is considerably less controversial, and is mainly held back at the moment by technological and cost considerations. Here, the idea is deploying technologies to actively remove the carbon dioxide that is in the atmosphere as a result of human emissions, which would also induce a cooling effect if deployed at adequate scale:


The two reports arrive following a dramatic growth in scientific publications and discussion about geoengineering over the past decade — fanned by climate concerns. The British Royal Society also recommended government-sanctioned and organized research into geoengineering in a report in 2009.

Up until now, the research studies on geoengineering published in scientific journals have generally relied upon computer simulations to study the hypothetical effects of various kinds of interventions. True outdoor experiments that change the world, rather than a simulacrum of it, are another matter — but if the framework outlined by the National Research Council were to be adopted, they could go carefully forward.

One researcher who has been thinking about such experiments is Jane Long, who was an associate director at the Lawrence Livermore National Laboratory and co-chaired the Bipartisan Policy Center’s study of geoengineering in 2011. In particular, she has considered small-scale experiments to explore marine cloud brightening, another albedo modification technique.

The idea here is that if clouds over the ocean were more white in color, they’d bounce back more solar radiation. So how would you conduct a field study of this idea?

“You might inject some salt particles in a coastal cloud belt and try to measure a change in albedo,” says Long. This modification could be done from shore, and then the cloud changes could be measured by aircraft from above.

Long, like the authors of the new report, is motivated by climate change concern. “We pretty accurately know that things are going to potentially be very bad in mid-century if we don’t get on top of the problem,” she says.