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Unformatted text preview: 1166 CREDIT: ALAN ROBOCK, USED BY PERMISSION OF WEATHERWISE AND HELDREF PUBLICATIONS PERSPECTIVES A ccording to the Inter- governmental Panel on Climate Change (IPCC) ( 1 ), global warming will soon have severe conse- quences for our planet. The IPCC also estimates ( 2 ) that mitigation would only cost ~0.1% of the global gross national product per year for the next 30 years, a price far smaller than the damage that would occur. As a potential route to mitigation, the old idea of “geoengineering” has got- ten much attention in the last 2 years ( 3 , 4 ). On page 1201 of this issue, Tilmes et al . ( 5 ) quantify the effects of one geoengineering approach— the introduction of additional aerosols into Earth’s strato- sphere, akin to a volcanic erup- tion—on high-latitude strato- spheric ozone concentrations. Geoengineering involves trying to reduce the amount of sunlight reaching Earth’s sur- face to compensate for the additional long-wave infrared radiation from greenhouse gases, thereby reducing or reversing global warming ( 6 ). Even if it works, there are prob- lems with this approach ( 7 ). If perceived to be a possible remedy for global warming, it would reduce societal pressure to reduce greenhouse gas emissions. It could reduce overall precipitation, particularly Asian and African summer monsoon rainfall, threaten- ing the food supply of billions. It would allow continued ocean acidification, because some of the carbon dioxide humans put into the atmosphere continues to accumulate in the ocean. Weather modification could be used as a weapon ( 8 ), thus violating the 1977 U.N. Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques. There would be rapid warming if geoengineering stopped sud- denly. If geoengineering worked, whose hand would be on the thermostat? How could the world agree on an optimal climate? Nevertheless, for some schemes, the bene- fits may outweigh the problems, especially if used on a temporary basis. To date, only some schemes have been investigated in detail. Furthermore, proponents of geoengineering, especially the fossil fuel industry, will con- tinue to push for its use. Sunshades in orbit around Earth ( 9 ) or cloud seeding to brighten them ( 10 ) have been proposed, but most geoengineering ideas focus on emulating explosive volcanic eruptions by injecting SO 2 or H 2 S into the stratosphere, pro- ducing a sulfuric acid cloud to scatter solar radiation back to space and cool the planet. Deciding whether this is a good idea or not requires detailed analysis of the costs, benefits, and harm to the planet that such a strategy would entail, and comparison to the same met- rics for mitigation and sequestration. Given the need for rapid mitigation, these ideas need rapid and thorough investigation....
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