Releasing engineered nano-sized disks or sulphuric acid, a condensable vapour, above the Earth are two novel approaches that offer advantages over simply putting sulphur dioxide gas into the atmosphere, says Dr. David Keith, a director in the Institute for Sustainable Energy, Environment and Economy and a Schulich School of Engineering professor
Scientists investigating geoengineering have so far looked mainly at injecting sulphur dioxide into the upper atmosphere. This approach imitates the way volcanoes create sulphuric acid aerosols, or sulphates, that will reflect solar radiation back into space—thereby cooling the planet’s surface.
One advantage of using sulphates is that scientists have some understanding of their effects in the atmosphere because of emissions from volcanoes such as
In his study in the Proceedings of the National Academic of Sciences, David Keith describes a new class of engineered nano-particles that might be used to offset global warming more efficiently and with fewer negative side-effects than using sulphates.
Aerosols could be injected into the upper atmosphere to engineer the climate by scattering incident sunlight so as to produce a cooling tendency that may mitigate the risks posed by the accumulation of greenhouse gases. Analysis of climate engineering has focused on sulfate aerosols. Here I examine the possibility that engineered nanoparticles could exploit photophoretic forces, enabling more control over particle distribution and lifetime than is possible with sulfates, perhaps allowing climate engineering to be accomplished with fewer side effects. The use of electrostatic or magnetic materials enables a class of photophoretic forces not found in nature. Photophoretic levitation could loft particles above the stratosphere, reducing their capacity to interfere with ozone chemistry; and, by increasing particle lifetimes, it would reduce the need for continual replenishment of the aerosol. Moreover, particles might be engineered to drift poleward enabling albedo modification to be tailored to counter polar warming while minimizing the impact on equatorial climates.
In a separate new study published in the journal Geophysical Research Letters, Keith and international scientists describe another geoengineering approach that may also offer advantages over injecting sulphur dioxide gas.
Releasing sulphuric acid, or another condensable vapour, from aircraft would give better control of particle size, thereby reflecting more solar radiation back into space while using fewer particles overall and reducing unwanted heating in the lower stratosphere, they say.
The study included computer modeling that showed that the sulphuric acid would quickly condense in a plume, forming smaller particles that would last longer in the stratosphere and be more effective in reflecting solar radiation than the large sulphates formed from sulphur dioxide gas.
Keith stresses that whether geoengineering technology is ever used, it shouldn’t be seen as a reason not to reduce man-made greenhouse gas emissions now accumulating in the atmosphere.
“Seat belts reduce the risk of being injured in accidents. But having a seat belt doesn’t mean you should drive drunk at 100 miles an hour,” he says