Issue Date: January 14, 2008
Interesting ideas have been suggested for decreasing atmospheric CO2 content, including the genetic modification of trees (C&EN, Nov. 19, 2007, page 6). However, these would take a long time to have significant effects, if they would ever work at all.
At least three large volcanic explosions are known to have caused global cooling effects by injecting dust and sulfur-containing particles into the stratosphere, reflecting some of the sun's heat: Tambora in 1815, Krakatoa in 1883, and Pinatubo in 1991. We could emulate these on a small scale by pumping an aqueous dispersion of fine clay (or possibly titania pigment) out of a refueling-type airplane at high altitude. If a desirable effect were measurable, a much larger experiment could be done, such as exploding a nuclear bomb in a ship full of clay.
Pinatubo seems to have caused a worldwide drought, according to the Aug. 17, 2007, National Geographic News (news.nationalgeographic.com/news/2007/08/070817-volcano-warming.html). On the other hand, in "Year without a Summer" (en.wikipedia.org/wiki/Year_without_a_summer), the Tambora explosion is reported to have caused more rainfall than usual. Weather modification experiments that the National Aeronautics & Space Administration could do for achieving global cooling would be smaller than the volcanoes, and they could involve different materials so that negative effects on rainfall might be avoided. Let's encourage our government to do such things instead of more Mars probes and Space Station exploits.
Daniel J. Shanefield
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