Climate Modification Schemes Come into Sharper Focus

A year and a half ago IEEE Spectrum published a feature article making the case that geoengineeringâ''deliberate modification of the earthâ''s climateâ''will have to be part of the solution to global warming. In recent months thereâ''s been an avalanche of geoengineering articles, for which weâ''d like to take credit, except that the main pulse came not from us but from Paul J. Crutzen, the Nobelist who codiscovered the mechanisms behind the creation and destruction of stratospheric ozone. In an August 2006 article, Crutzen put his considerable prestige behind engineered climate modification, specifically the idea of pumping sulfur dioxide into the atmosphere to reflect sunlight and cool the earth.

Crutzen is a starting point for a feature in this monthâ''s Scientific American by science writer Robert Kunzig, who surveys three major approaches: pumping SO2 to create a â''stratospheric sulfate sunshadeâ''; telescope designer Roger Angelâ''s concept for building a sunshield out of small silicon nitride disks at the Earth-Sun Lagrangian; andâ''perhaps most arrestinglyâ''whipping sea salt up into the atmosphere to speed and enhance cloud formation over the oceans, using so-called Flettner ships.

Curiously, Scientific American prefaces its geoengineering feature with an editorialâ''an eloquent and well-reasoned one, to be sureâ''arguing that undue emphasis on climate modification puts the cart before the horse: â''Proponents . . . see geoengineering merely as a stopgap measure to buy time for emissions reductions, which may take decades to achieve. But what is the point of buying time? Every year that we put off those reductions makes our job that much harder.â''

This blogger agrees that emissions reduction must take priority. But wouldnâ''t it still make sense to have geoengineering tools at our disposal, to use if catastrophic climate changes start to take place, despite the worldâ''s efforts at emissions reduction? New Zealand ecologist Philip Boyd, in an article and interview, says we should critically evaluate the main geoengineering ideas now, throw away the ones that are plainly no good, and put the remaining ones in a â''climate change toolbox,â'' ready for use in a climate emergency.

If youâ''re looking for criteria to decide which geoengineering ideas make sense and which donâ''t, a good place to start is the May-June issue of The Bulletin of the Atomic Scientists, which listed â''20 reasons why geoengineering may be a bad idea.â'' (Risks of unintended consequences, which loom large in Kunzigâ''s article and SciAmâ''s critical assessment, rank only 20 on the list compiled by Rutgers ecologist Alan Robock.) The top two are the uneven regional effects to be expected from sulfate shielding and the continued acidification of the oceans that will take place irrespective of counter-warming measures.

A technical article that Robock wrote this year with two coauthors evaluated regional climate effects from injection of SO2 in the tropics and Arctic regions. They found that sulfate shields â''would disrupt the Asian and African summer monsoons, reducing precipitation to the food supply for billions of people.â''

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