Artist's concept of a spray ship that could whiten clouds with salt water.
Credit: Institute of Mechanical Engineers
None of the scientists in the room so much as blinked when David Keith suggested saving the world with spy planes spraying sulphuric acid.
Keith, a physicist at the University of Calgary in Canada, was facing an audience not likely to be shocked: nearly 200 other researchers, some of whom had their own radical ideas for fighting global warming. His concept was to spray a mist of sulphuric acid high in the stratosphere to form particles called sulphate aerosols, which would act like a sprinkling of tiny sunshades for the overheating Earth.
Keith's idea may sound outrageous, but it is just one of many proposals for bumping the global thermostat down a couple of degrees by tinkering directly with the planet's heating and cooling systems. Plans to cool the Earth range from shading it to fertilizing it, from seeding clouds to building massive supersuckers that filter greenhouse gases from the air.
The schemes are all part of a growing field known as geoengineering: a subject once taboo for all but the scientific fringe, but now beginning to go mainstream.
So far the tinkering happens mainly in computer models, where researchers are trying to figure out geoengineering's potential side effects. Yet some technologies are in the prototype stage, governments are starting to consider geoengineering seriously and budding geoengineers are working out how to proceed safely, and ethically, with real-world experiments.
"It truly is asking giant questions which nobody really knows the answers to," Keith says - "like how we manage the whole Earth."
In March, Keith and other experts met in a dimly lit chapel-turned-auditorium at the Asilomar resort near Monterey, California. In 1975, molecular biologists met at the same resort to write landmark guidelines to regulate DNA experiments. This time around, cloud physicists, legal scholars and government bureaucrats debated the relative merits of brightening clouds versus building artificial trees.
In the end, the meeting-goers concluded that geoengineering research should cautiously proceed, in case Earth's climate proves broken beyond the current means of repair: ratcheting down fossil fuel use.
Researchers have kicked around the idea of large-scale climate manipulation since at least the 1960s, when Soviet scientists suggested damming the Bering Strait as part of a scheme to warm Siberia and free shipping lanes of sea ice. But mainstream scientific attention began only about five years ago.
In a 2006 editorial in the journal Climatic Change, atmospheric chemist Paul Crutzen suggested that sulphate aerosols might be used to intentionally cool the planet. Coming from a scientist who had shared the 1995 Nobel Prize in Chemistry for helping explain how man-made chemicals ate away the Earth's protective ozone layer, the idea gained some traction. Geoengineers poked their heads from the closet tentatively at first. But soon, ideas multiplied.
