The call to at least consider audacious geo-engineering steps that would fill the stratosphere with globe-cooling aerosols to check global warming got louder last week. In Science, Tom M. L. Wigley of the National Center for Atmospheric Research, in Boulder, Colo., writes that reducing carbon dioxide emissions is the long-term solution to global warming but that nearer term engineering of the atmosphere might provide "additional time to address the economic and technological challenges faced by a mitigation-only approach" (DOI: 10.1126/science.1131728).
Last month, Nobelist Paul J. Crutzen of the Max Planck Institute for Chemistry, in Mainz, Germany, made headlines with an essay in the journal Climatic Change calling for more research into the pros and cons of injecting sulfate-based aerosols into the stratosphere as a sunlight-reflecting, cooling foil to global warming (C&EN, Aug. 7, page 19).
Wigley has quite visibly joined Crutzen in this view, this time running several aerosol-producing scenarios through a simple atmospheric model. Adding just 5 million metric tons of sulfur dioxide annually to the stratosphere to produce sunlight-reflecting clouds or a light-scattering haze "would have a significant influence," Wigley says. The 1991 Mount Pinatubo eruption belched twice that amount of sulfur into the stratosphere and had a temporary cooling effect for a few years.
Rutgers University climate scientist Alan Robock worries that the Wigley analysis gives short shrift to uncertainties and ignores such factors as the warming spike that occurred in northern latitudes in the winter following the Pinatubo eruption. Constant aerosol production also could mean "we wouldn't have blue skies anymore," and it could reduce incoming solar radiation enough to hobble such imperatives as replacing fossil fuel with solar energy technologies, Robock says.