Cover of the NRC report, 'Climate Intervention: Reflecting Sunlight to Cool Earth'. Graphic: NRC

By Raymond T. Pierrehumbert
10 February 2015

(Slate) – Some years ago, in the question-and-answer session after a lecture at the American Geophysical Union, I described certain geoengineering proposals as “barking mad.” The remark went rather viral in the geoengineering community. The climate-hacking proposals I was referring to were schemes that attempt to cancel out some of the effects of human-caused global warming by squirting various substances into the atmosphere that would reflect more sunlight back to space. Schemes that were lovingly called “solar radiation management” by geoengineering boosters. Earlier I had referred to the perilous state such schemes would put our Earth into as being analogous to the fate of poor Damocles, cowering under a sword precariously suspended by a single thread.

This week, the National Research Council (NRC) is releasing a report on climate engineering that deals with exactly those proposals I found most terrifying. The report even recommends the creation of a research program addressing these proposals. I am a co-author of this report. Does this mean I’ve had a change of heart?


The nearly two years’ worth of reading and animated discussions that went into this study have convinced me more than ever that the idea of “fixing” the climate by hacking the Earth’s reflection of sunlight is wildly, utterly, howlingly barking mad. In fact, though the report is couched in language more nuanced than what I myself would prefer, there is really nothing in it that is inconsistent with my earlier appraisals.

Even the terminology used in the report signals a palpable change in the framing of the discussion. The actions discussed for the most part are referred to as “climate intervention,” rather than “climate engineering” (or the common but confusing term geoengineering). Engineering is something you do to a system you understand very well, where you can try out new techniques thoroughly at a small scale before staking peoples’ lives on them. Hacking the climate is different—we have only one planet to live on, and can’t afford any big mistakes. Many of the climate “engineering” proposals are akin to turning the world’s whole population into passengers on a largely untested new fleet of hypersonic airplanes.

Most previous literature has referred to schemes to increase the proportion of sunlight reflected back to space as solar radiation management, as if it were something routine and businesslike, along the lines of “inventory management” or “personnel management.” It is far from clear, however, that solar radiation can be managed in any meaningful sense of the word. The NRC report instead uses the more neutral term “albedo modification.” Albedo is the scientific term for the proportion of sunlight reflected back to space. If the Earth had 100 percent albedo, it would reflect all sunlight back to space and be a frozen ice ball some tens of degrees above absolute zero, heated only by the trickle of heat leaking out from its interior. Earth’s current albedo is about 30 percent, with much of the reflection caused by clouds and snow cover. I myself prefer the term “albedo hacking,” but “albedo modification” does pretty well. My colleague and report co-author James Fleming has called such schemes “untested and untestable, and dangerous beyond belief.” (A companion report also discusses less problematic, if currently expensive, schemes for removing carbon dioxide from the atmosphere. Many of those would be well worth doing if they ever became economical.) [more]

Climate Hacking Is Barking Mad



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