The Copenhagen climate meeting was a big disappointment. Sen. Lindsey Graham now says the cap-and-trade bills "are going nowhere." So despite continued work toward cutting greenhouse emissions, we may see in the coming months a renewed interest in geoengineering—the deliberate, large-scale manipulation of the atmosphere—in an attempt to ward off the dangers of climate change.
The once-rogue concept of planet-hacking has come a long way in just three years: from key private meetings among scientists, to sophisticated computer modeling papers (PDF), to serious investigations of the idea by the British Royal Society and the U.S. National Academy of Sciences. This week the discussion moves into a new phase: a debate over how actual field tests for geoengineering should be implemented, regulated and, in fact, whether their results would even help us to understand the most severe risks of deployment at all. In three opinion pieces published in the premiere science journals—one in Nature yesterday, and two in Science today—scientists from across the world offered differing takes on the future of internationally coordinated testing. But their back-and-forth over which experiments might be best and what sort of political treaties would be necessary raises a distressing possibility: It's not just that geoengineering tests will be difficult. It's that the problems they invite would be so diverse—and their results so inconclusive—that we're likely to skip the testing altogether. If countries are going to hack the stratosphere, they may just do it full-bore in the face of disaster.
The three papers naturally focus on what's considered the fastest and most feasible form of geoengineering—the sun-blocking method some call the Pinatubo Option. If deployed, this would mimic the cooling effect of volcanoes by putting a cloud of particles in the upper atmosphere, where they could scatter a small percentage of the sun's rays. (It's named after the eruption of Mount Pinatubo in 1991. That event cooled the globe 1 degree Farenheit in less than a year by spewing 10 million tons of sulfur pollution into the stratosphere.) Scientists have proposed creating a cloud of sulfuric acid or other particles using airplanes, naval guns, or hoses suspended by balloons. So, can we do a practice run of the Pinatubo Option?
The easiest experiments would involve the design of geoengineering hardware and tools to monitor the dispersal of particles from the ground. We might be able to look at how very small particle clouds affect local ozone levels or weather conditions at low altitudes. Those small-scale tests aren't likely to affect the climate at all, but they wouldn't give us very much information on the gravest risks of geoengineering, either. A more useful set of tests would be medium-scale field applications of the Pinatubo Option—in the form of releasing particles into the sky for years, enough time to alter the climate. In theory, this might help us to understand how dimming the globe effectively might shift circulation patterns or perturb the stratospheric ozone layer. But that's where things get dicey, according to University of Calgary physicist David Keith and colleagues writing in Nature. The trick is to balance usefulness with risk in experiments. Some compare (PDF) the ideal field-testing regime for the Pinatubo Option to a clinical trial for a new pharmaceutical drug, in which scientists incrementally trade higher risks for more useful data. They start with mice and increase the dosage in the trial gradually, with each step mitigating the dangers of the next one. The larger doses may have more side effects, but they also yield more information about the drug when taken at full strength.
Keith advocates such an approach for geoengineering, calling for "a carefully designed, incremental, transparent and international program" of sun-blocking approaches like the Pinatubo Option. "It would be reckless to conduct the first large-scale [sun-blocking] tests in an emergency," he writes. "Experiments should expand gradually to produce barely detectable climate effects and reveal unexpected problems, yet small enough … to limit risks." But he acknowledges that even an experiment involving one-tenth the sulfur of Pinatubo would involve "nontrivial" dangers.
In their Science article, Alan Robock of Rutgers and colleagues underscore that point. The group has used a NASA computer model to simulate the spraying of a sulfur dose roughly one-seventh as large as Pinatubo, released annually over the Arctic for two decades. (The comparison is messy, but deploying the Pinatubo Option to compensate for expected global warming would use roughly half as much sulfur as was released by the volcano in 1991.) Given the extreme variability in Earth's climate system, it might take an experiment of that size or bigger to get useful data on major side effects, Robock says, and the impacts of such a test would be profound. In the simulation, global rain and snowfall was reduced and the summer monsoon over Africa and Asia was weakened. Some models say that plants, including crops, might thrive with less heat; Robock fears testing the Pinatubo Option could affect "the food and water supplies of 2 billion people."
So one group of scientists argues that by gradually increasing the size of our experiments, we can get as much data as possible with minimal risk. Another says that only a dangerous, full-scale deployment can shed light on the crucial issue of how effective a particular dose will be. The point isn't who's right—it's that countries won't be willing to run these potentially harmful tests if scientists can't agree on how useful they'll be.
Indeed, those disputes might continue even after a given set of tests was completed. In the case of another potential form of geoengineering—adding trace amounts of iron to the ocean to grow algae to suck carbon out of the sky—we've already seen an example of how this plays out. A dozen small-scale experiments to grow algae blooms have been conducted around the world's oceans since 1993, and there's still no consensus among oceanographers as to what the results suggest. Some scientists say a few of the experiments have worked to permanently sequester some carbon in the deep ocean; others say that carbon was recycled back to the surface.
The authors of the Nature and Science papers hope that international agreements or treaties could be put in place ahead of time, to avert ecological harm or political strife. The surest way to minimize risks would be Keith's approach: Conduct internationally-coordinated, modest tests over a decade or more, teasing out the cooling signal over time. But given the inevitable political and scientific conflicts that would arise, such a long series of tests will just give countries more chances to bail on the project. That's why we may not see any medium-scale, informative tests until we're unlucky enough to face with looming, catastrophic changes in the climate. At that point, we'll have no choice but to go all out with a full deployment, with little more than computer-based risk estimates to guide us. From one dangerous global experiment—our current carbon binge—to another.