August 31, 2012
Climate change used to be thought of as a long-term worry; now, there’s good reason to believe we’re already encountering its effects. As the problem grows more urgent, some say we ought to take a radical approach: Instead of struggling in vain to limit greenhouse gas emissions, we should try to engineer systemsto directly stop the warming of the planet.
This approach is known as geoengineering, and it might be the most controversial area in climate science.
The term encompasses a wide variety of techniques. One company tried to fertilize the ocean with iron, to encourage the growth of algae to absorb excess carbon dioxide. Other scientists have suggested spraying clouds with seawater to increase their whiteness—and thus reflectivity—reducing warming by bouncing light back out to space. The U.S. government has even considered gigantic, sun-blocking mirrors in outer space as a last-ditch option if climate change hits a tipping point.
The most debated suggestion, though, is inspired by a natural phenomenon: Massive volcanic eruptions can trigger several years of global cooling because they by suspend sulfur aerosols and other particulate matter high enough in the atmosphere where they remain aloft for years, blocking a small fraction of sunlight. This effect could be mimicked using aircraft, artillery or even suspended pipes to send sulfate particles into the atmosphere where they would counteract the effect of rising greenhouse gas concentrations.
Now, for the first time, a team of scientists has specifically analyzed the immediate financial costs of employing such a technique. Their results, published yesterday in the journal Environmental Research Letters, might be seen as encouraging by advocates of geoengineering—but depressing for everyone hoping to limit greenhouse gas emissions.
The researchers, from Aurora Flight Sciences, Harvard University and Carnegie Mellon University, found that continuously delivering materials into the stratosphere to deflect sunlight could theoretically be accomplished with current technologies and could cost as little as $5 billion per year worldwide. Although this might sound like a large sum, reducing emissions enough to prevent carbon dioxide levels from surpassing 450 ppm—a figure often cited as a stabilization target to prevent significant warming—would cost anywhere from $200 to $2,000 billion, making geoengineering seem like a relative bargain.
The detailed cost analysis evaluated systems that could deliver 1 million tonnes of sulfates annually to altitudes greater than 11 miles, well into the stratosphere, between 30°N and 30°S for the entire planet. In comparing six different techniques—the use of existing aircraft, a new aircraft designed to perform at high altitudes, a new hybrid airship, rockets, guns and suspended pipes—the authors found that using existing or newly designed aircraft would be the most cost-effective options.
Designing aircraft specifically for performance at high altitude, they found, would likely be less expensive than modifying current aircraft for the task, although both options would be possible given current technology. Using guns and rockets or suspended pipes would be more costly, largely because they wouldn’t be reusable, whereas devoted aircraft could deliver the particles to the stratosphere time and time again. The most fanciful option—a large gas pipe that would rise miles into the sky, perhaps supported by helium-filled platforms—could be the most expensive, due to the cost of developing such an unprecedented system and the overall uncertainty involved.
The authors note, though, that the unknowns and potential risks of this type of geoengineering could outweigh the reduced pricetag. For one, it treats a symptom of climate change (a warmer atmosphere) rather than the cause (greenhouse gas concentrations), so it does nothing to address other related problems, such as ocean acidification. There’s also the fact that once such measures induce dependence: If we started them on a global scale, we’d have to continue indefinitely, or risk an accelerated return of the climate to where it would have been without any action.
Most alarmingly, intentionally pumping millions of tons of aerosols into the atmosphere is an experiment for which we have no precedent. Our understanding of the climate is still incomplete, so embarking on an intentional plan to re-engineer it (after already doing so quite unintentionally) could lead to unexpected consequences. Other researchers have noted that deploying sulfates into the stratosphere could cause ozone depletion, trigger drought, alter cloud formation and might even counterintuitively cause more warming.
This is one area of science where some say that merely performing research can irresponsibly alter the actual outcome of events. Once concrete information about geoengineering techniques is out there, it could sap public support for emissions reductions and provide a politically handy “backup plan” for policymakers. Additionally, it raises the frightening idea of unilateral deployment: With the world’s nations seemingly incapable of a binding agreement to reduce emissions, an island nation facing sea level rise could simply start re-engineering the atmosphere for its own survival.
This study helps us better understand the visible expenses of geoengineering as a solution for climate change. It’s long-term costs, though, are still up in the air.
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