Geoengineering schemes: pros and cons

By Gregory M. Lamb, Staff writer / May 3, 2010

Ideas to block or reflect sunlight:

• Buildings with white roofs and light-colored pavement reflect more sunlight back into space. Pros: Little chance of unintended effects. Con: Wouldn’t create a significant climate change by itself.• Send sulfur dioxide particles into upper atmosphere. Pro: Likely to work, since this happens in nature when volcanoes erupt. Cons: Could change rainfall patterns, making it wetter in some places, drier in others. Might thin the ozone layer or have other unintended effects. Would have to be done repeatedly.• Space-based mirrors. Orbiting mirrors would reflect sunlight away from Earth. Pro: Could be concentrated over key areas needing cooling, such as Earth’s poles. Con: Expensive.• Cloud whitening. Ships would spray seawater into the lower atmosphere, leaving shiny salt crystals that brighten clouds and reflect sunlight. Pro: Uses only seawater so may be legal under current international law. Con: Would have to be done perpetually.• Ocean whitening (microbubbles). Ships would leave wakes full of tiny air bubbles, which are whiter and more reflective than the rest of the ocean surface. Pros and cons: See cloud whitening.• Fields of light-colored plants, perhaps genetically altered to be reflective. Pro: Would reflect sunlight back into space. Con: Might cause unintended consequences.

Ideas to remove CO2 from the atmosphere (all take a long time to create a substantial effect):

• Plant (genetically modified?) trees to absorb CO2. Pro: It works and has little risk. Cons: Genetic modification could pose risks. Not likely to have much effect by itself.• Create artificial trees to absorb CO2. Pro: Would remove CO2. Con: Costly, unproven technology.• Ocean fertilization with iron or other nutrients. Pros: Algae blooms would suck in CO2 and then sink to the ocean depths. Cons: One study suggested the blooms might be toxic. Might have other effects.

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