Scientist offers better ways to engineer Earth's climate to blunt global warming
more efficiently, and with fewer negative side effects, than using sulphates.
According to Keith, the distribution of engineered nano-particles above the Earth could be more controlled and less likely to harm the planet’s protective ozone layer.
Sulphates also have unwanted side-effects, ranging from reducing the electricity output from certain solar power systems, to speeding up the chemical process that breaks down the ozone layer.
Engineered nano-particles could be designed as thin disks and built with electric or magnetic materials that would enable them to be levitated or oriented in the atmosphere to reflect the most solar radiation.
It may also be possible to control the position of particles above the Earth. In theory, the particles might be engineered to drift toward Earth’s poles, to reduce solar radiation in polar regions and counter the melting of ice that speeds up polar warming — known as the ice-albedo feedback.
“Such an ability might be relevant in the event that warming triggers rapid deglaciation,” Keith’s study says. “Engineered nano-particles would first need to be tested in laboratories, with only short-lived particles initially deployed in the atmosphere so any effects could be easily reversible,” says Keith.
Research would also be needed to determine whether such nano-particles could be effectively distributed, given the complex interplay of forces in the atmosphere, and how much cooling might be achieved at the planet’s surface.
It is also unknown whether the amount of particles needed — about one trillion kilograms per year or ten million tons over ten years — could be manufactured and deployed at a reasonable cost.
Keith, however, notes another study which looked at the cost of putting natural sulphates into the stratosphere. “You could manipulate the Earth’s climate at large scale for a cost that’s of the order of $1 billion a year. It sounds like a lot of money, but compared to the costs of managing other environmental problems or climate change, that is peanuts.”
“This is not an argument to do it, only an indication that risk, not cost, will be the deciding issue,” he adds.
In a separate new study to be 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 vapor, from an aircraft would give better control of particle size. The study says this would reflect more solar radiation back into space, while using fewer particles overall and reducing unwanted heating in the lower stratosphere.
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 should not 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.
—Read more D. W. Keith, “Photophoretic levitation of engineered aerosols for geoengineering,” Proceedings of the National Academy of Sciences (in press); and Jeffrey R. Pierce, Debra K. Weisenstein, Patricia Heckendorn, Thomas Peter, and David W. Keith, “Efficient formation of stratospheric aerosol for geoengineering by emission of condensible vapor from aircraft,” Geophysical Research Letters (in press). To see .pdf versions of the two studies before they are published, send an e-mail to robertsh@ucalgary.ca to ask for a password.
