In 2006, Nobel laureate Paul Crutzen suggested that we might need to start deliberately engineering the climate if no progress could be made on curbing our emissions. Since then, atmospheric concentrations of CO2 have continued to rise. So it’s perhaps no surprise that what once seemed like a outlandish idea has recently become a subject of serious scientific endeavour.
Injecting sulphate aerosols into the stratosphere has been one of the various proposed ‘geoengineering’ schemes; others include fertilizing the ocean with iron and stimulating cloud formation.
A new study [subscription] led by Alan Robock at Rutgers University in New Jersey now looks at the prospects for stratospheric ‘geoengineering’ in terms of its benefits, costs and risks. Writing in Geophysical Research Letters, they highlight the pros of injecting a sulphate gas into the stratosphere in the face of a climate catastrophe: it would cool temperatures, stop the melting of sea and land-based ice, slow sea level rise and increase the planet’s ability to sequester greenhouse gas.
But if the public sees geoengineering as a low-cost and easy ‘solution’ to climate change, then it could erode backing for mitigation, say the researchers, who weight the benefits against the associated risks and costs. Among the dangers of such a scheme is the risk of substantial ozone depletion, including delayed the recovery of the Antarctic ozone hole, they say. Other risks include regional drought, ocean acidification, a reduction in sunlight and the end of blue skies. The cost would ultimately depend on how the gas was deployed. Robock and colleagues say that using existing US military planes would be the cheapest option, at roughly several billion dollars per year. Lofting the gas using artillery shells or balloons would be more expensive. Other options, such as pumping the gas through a tall tower or lifting it into the stratosphere using a space elevator, may be possible in the future, say the scientists, but their cost cannot be evaluated just yet.
The dangers, rather than the cost, will ultimately limit the potential of geoengineering as a solution to climate change, conclude Robock’s team.