The concept of active human efforts to artificially limit or reverse climate change has been around for some years. Collectively called geoengineering, many such plans, some more fanciful than others, have been proposed by the scientific community, and several were discussed during the final days of the AGU Joint Assembly in Toronto.
One plan, described by Alan Robock of Rutgers University, New Jersey, US, would involve continuously placing fine particles of sulphur dioxide (SO2) into the stratosphere, to block sunlight from reaching Earth’s surface. This, proponents say, would be benign, simply mimicking the effect of large volcanic eruptions, and simulations confirm that northern hemisphere or even global cooling would follow.
Although there is currently no way to do it, the problem is not the technology, Robock said in an interview, amplifying on his oral presentation at the meeting. The technology to inject SO2 particles into the stratosphere might not be that difficult; high altitude military planes could be adapted to do it, he suggested, although there are questions about their ability to deliver particles of the appropriate size. Regardless, the ancillary effects of the experiment could be devastating, he said, by reducing the amount of precipitation associated with the summer monsoon in Asia and Africa, thereby threatening the food supply for billions of people.
A secondary proposal that Robock described in his presentation would provide the SO2 seeding only in the Arctic. The problem is, he said, that winds blow the particles southward, with comparable effects on the monsoons, according to simulations, so there would be no advantage to year-round Arctic-only seeding.
Finally, there is a proposal to seed only in the Arctic, and only in the spring or summer, since there is no point in doing so when there is no sunlight at those latitudes. This would indeed provide at least local cooling, “save the polar bears, save Greenland from melting, and test out the techniques,” Robock said.
Still, there are many reasons why even this limited experiment would be a bad idea, he insisted, listing some of them. It would cost billions of dollars and produce regional drought and ozone depletion, provide less sunlight for solar power and make the sky less blue, while interfering with Earth-based telescopes. The full list will appear in a paper Robock and colleagues have submitted to Geophysical Research Letters. It would be necessary to quantify both the beneficial and negative effects of the SO2 seeding proposal, in any of its variations, Robock concluded, in order for policy-makers to reach informed decisions, and this has yet to be done.
The halls of the Metro Toronto Convention Centre grew quieter as the last afternoon of Joint Assembly drew to a close. Some participants had already departed by yesterday afternoon, wending their way up and down seemingly endless escalators, across the sky bridge spanning Canada’s main railway line—10 tracks wide at this point—and toward the Lake Ontario waterfront on one side and downtown pubs and restaurants on the other. Some even headed straight up for the view at the top of the adjacent CN Tower, Canada’s tallest structure. Scientists and reporters alike are already gearing up for AGU Fall Meeting, where they will meet again as always in December in San Francisco.
Harvey Leifert is a freelance science writer