By Thomas Sumner

The ideas seem lifted from a James Bond super villain’s dastardly plot: carpeting the Earth with whitened clouds, constructing giant solar reflectors in space, using chemicals to change the makeup of the atmosphere. But with scientific models predicting potentially devastating changes in the world’s climate, seemingly impractical and improbable geoengineering solutions become more and more alluring.

This month at the National Academy of Sciences in Washington D.C., a 16-person ad hoc committee of scientists held its second meeting to discuss the practicality of various methods of purposefully changing Earth’s environment to combat climate change, sometimes called climate engineering or geoengineering. Convened purely for investigation and discussion rather than making recommendations, the group cast a wide net for ideas, even those they might ultimately reject as made- for-Hollywood only.

One geoengineering approach would inject aerosols into the stratosphere to reflect away solar radiation. A 2009 scientific paper evaluated benefits, risks, and costs of using aircraft, balloons, and other means to loft aerosols, as depicted in this figure from the paper. Credit: Brian West.

The first morning of the September 10-11meeting, Harvard University geology professor Daniel Schrag addressed the committee, laying out the climate issues geoengineering hopes to solve.

Schrag said the consequences of climate change—sea level rise, more severe weather extremes, ocean acidification—demand action. However, even in a best case scenario with a perfect political climate and a quick move to low-emission energy sources, Schrag said fixing carbon dioxide emissions within the foreseeable future would be impossible.

“Scientifically we can’t fix this problem for 100 years,” he argued.

This lack of a single simple and viable solution is what makes geoengineering worth considering, according to Gary Geernaert, director of the US Department of Energy’s Climate and Environmental Sciences Division, who spoke to the committee.

“There’s no silver bullet for climate change,” said Geernaert said. “We need to look at all the available solutions.”

Wild potential plans

Geoengineering breaks down into two main approaches: capturing carbon and reflecting solar radiation.

The first aims to remove carbon dioxide from the atmosphere, thereby reducing the greenhouse effect warming the planet. The second hopes to create a cooling effect by bouncing solar radiation away before it can cause warming. Tactics include dumping large amounts of reflective asteroid dust into orbit around Earth, making clouds whiter, seeding the creation of more clouds and covering rooftops with reflective materials.

The committee gave respectful attention to schemes that even their proponents consider iffy. Schrag, for instance, mentioned an “impractical” idea he and his colleagues had to create a massive acid exchange to remove carbon from the air.

When carbon dioxide is mixed with water, it forms a mild acid called carbonic acid (carbonated water). Limestone can neutralize the acid, as it does in caves, where the carbon gets bound up in stalactites and stalagmites.

Schrag’s proposal uses massive amounts of quicklime – the product of breaking down limestone using heat – to neutralize atmospheric and ocean carbon. Multiple times throughout his description Schrag branded the plan “completely impractical” – it requires massive amounts of energy and manpower to operate – yet the committee asked thoughtful follow-up questions.

Unforeseen consequences

Before a geoengineering project can move forward, scientists need to know the impacts it will have—both good and bad. Running large-scale tests is too dangerous, since any unexpected negative consequences would be similarly large-scale, according to NASA scientist Ralph Kahn.

“A lot more geoscience has to be done before we can consider geoengineering,” said Kahn.

Smaller tests may be safer, but any potential benefits would likely be too small to quantify. Luckily natural analogs can provide insights into the potential effects of geoengineering projects. Volcanoes, for instance, blast particles into the atmosphere that can reflect the Sun’s rays away from Earth. Several proposed geoengineering projects suggest emulating this effect with artificial volcanos. By observing real volcanos, scientists might see the potential downsides beforehand, preventing swapping one man-made climate disaster for another.

Over the course of the meeting, 15 experts addressed the committee, ranging into politics and ethics as well as Earth-altering schemes. In coming months, the committee will assemble a report on three or four example techniques, weighing their potential risks and consequences.

– Thomas Sumner is AGU’s science writing intern