Aside from the political and economic risks associated with geoengineering, which we explored in Monday’s radio segment on The California Report, critics warn that climate intervention strategies involve some serious potential environmental consequences as well.

In one 2008 study, scientists at the Lawrence Livermore National Lab found that one of the leading geoengineering ideas–blocking solar radiation by pumping sulfur aerosol into the stratosphere–may lead to decreased precipitation across the globe.

Climate scientist Phil Duffy, now of the education organization Climate Central and one of the authors of the 2008 study, says that the decrease in precipitation would follow a slowdown of the overall hydrologic cycle, caused by a decrease in evaporation.  Blocking sunlight reduces evaporation, and since what comes down much first go up, less evaporation means less rain and snow.  As this geoengineering scheme is being proposed as an emergency brake to counter effects of climate change like drought, this is problematic news.

Stratospheric sulfur injection could also seriously damage the Earth’s ozone layer above the Arctic, another 2008 study found.  And opponents fear that it could lead to acid rain, which could exacerbate the growing problem of ocean acidification.

Ken Caldeira of the Carnegie Institute for Science says that computer modeling from his lab indicates that even if the strategy improved living conditions for 90% of the people on the planet, it’s likely that 10% would suffer negative environmental consequences, and, he says, it would be hard to predict where on the planet that 10% would be.

“We’ve come to the conclusion that there are no experiments that will tell you ahead of time what the regional effects will be,” said Caldeira.

Another high-profile strategy involves fertilizing the ocean with iron as a way to  encourage algae blooms for carbon sequestration.  Algae absorb carbon dioxide as they grow, and the theory is that when they die, they’ll sink to the bottom of the ocean and take the CO2 with it.  There is conflicting research about whether this could work as a long-term sequestration strategy, but a recent study suggests that regardless of whether it’s effective at sequestering CO2 or not, fertilizing the oceans with iron could harm marine ecosystems.   The research shows that increases in algae from the genus Pseudonitzschia can promote concentrations of domoic acid, a poison that can kill birds and marine mammals.  Richard Black has more on the new findings at the BBC website.

For more on the potential risks of geoengineering, Alan Robock‘s article “20 Reasons Why Geoengineering May Be a Bad Idea” appears in the May/June issue of the Bulletin of Atomic Scientists.