Geoengineering techniques aim to slow global warming through the use of human-made changes to the Earth's land, seas or atmosphere. But new research shows that the use of geoengineering to do environmental good may cause other environmental harm. In a symposium at the Ecological Society of America's Annual Meeting, ecologists discuss the viability of geoengineering, concluding that it is potentially dangerous at the global scale, where the risks outweigh the benefits.

"The bigger the scale of the approach, the riskier it is for the environment," says session organizer Robert Jackson , director of Duke University's Center on Global Change. Global alterations of Earth's natural cycles have too many uncertainties to be viable with our current level of understanding, he says.

One global-scale geoengineering method, termed atmospheric seeding, would cool the climate by releasing light-colored sulfur particles or other aerosols into the atmosphere to reflect the sun's rays back into space. This approach mimics what happens naturally when volcanoes erupt; in 1991, for instance, an eruption of Mount Pinatubo in the Philippines cooled the Earth by 0.9 degrees Fahrenheit.

But Simone Tilmes of the National Center for Atmospheric Research argues that despite its potential to create overall cooling, atmospheric seeding could cause significant changes in localized temperature and precipitation. Her simulations also predict that sulfur seeding could destroy atmospheric ozone, leading to increased ultraviolet radiation reaching the Earth's surface. "An increase in ozone depletion over the Arctic could lead to dangerous levels of ultraviolet light hitting the Earth's surface," she says. "In this case, the recovery of the ozone hole over the Antarctic could be delayed by decades."

Another large-scale geoengineering scheme is fertilizing the oceans with iron to increase carbon uptake from the atmosphere. Charles Miller of Oregon State University says that ocean fertilization could create a rise in iron-limited phytoplankton populations, which by dying and sinking would use enough oxygen to create extensive dead zones in the oceans. In addition, he says, the maximum possible rate of ocean iron fertilization could only offset a small fraction of the current rate of carbon burning by humans.

Ocean fertilization also does not alleviate the increasing problem of ocean acidification, caused by carbon dioxide from the increasingly carbon-rich atmosphere dissolving into seawater. In fact, Miller says, ocean fertilization schemes will likely exacerbate this problem. "Any large-scale fertilization could cause risks to ocean ecosystems as great as those of global warming itself," he says.

Despite its apparent hazards at the global scale, Jackson thinks that research should continue on safer ways to use geoengineering at a smaller scale. Geologic sequestration, sometimes known as CO2 capture and storage, takes CO2 out of the atmosphere and stores it in underground reservoirs. Jackson says that this solution has the potential to store more than a century's worth of electric power emissions at a relatively low cost. He notes, however, that some potential risks of geologic sequestration include carbon leakage and the potential for interactions with groundwater.

But on the planetary scale, most ecologists are skeptical of climate engineering. "Playing with the Earth's climate is a dangerous game with unclear rules," says Jackson. "We need more direct ways to tackle global warming, including energy efficiency, reduced consumption, and investment in renewable energy sources."

Clifford Duke, Director of Science Programs at the Ecological Society of America, is co-organizer of the symposium. Additional speakers include David Keith from the University of Calgary and Phillip Duffy from Climate Central, Inc. The researchers will present their results in "Symposium 21 - The Environmental Effects of Geoengineering" on August 6, 2009 in the Albuquerque Convention Center.

(Science Daily, 07/08/2009)