Enviro Monday: Could solar geoengineering be a solution to global warming?

In the search for solutions to climate change, researchers from SEAS have identified an aerosol made from calcite – a common antacid medication – that could reflect sunlight while repairing the ozone layer.

Reducing emissions of greenhouse gases is not enough

The planet is warming at an unprecedented rate, and reducing emissions of greenhouse gases alone is not enough to alleviate the danger to the survival of the inhabitants of the planet.

One drastic idea is solar geoengineering – injecting light-reflecting sulfate aerosols into the stratosphere to cool the planet.

Researchers know that large amounts of aerosols can significantly cool the planet; the effect has been observed after large volcanic eruptions. But these sulfate aerosols also carry significant risks. The biggest known risk is that they produce sulfuric acid in the stratosphere, which damages ozone. Since the ozone layer absorbs ultraviolet light from the sun, its depletion can lead to increased rates of skin cancer, eye damage, and other adverse consequences.

An aerosol that may cool the planet and repair ozone damage

Now SEAS researchers have identified an aerosol for solar geoengineering that may be able to cool the planet while simultaneously repairing ozone damage.

Previous research focused on ways to limit the ozone-damaging reactions produced by nonreactive aerosols. But Harvard Professors David Keith and Frank Keutsch and others took a completely different approach, targeting aerosols that are highly reactive.

“Anytime you introduce even initially unreactive surfaces into the stratosphere, you get reactions that ultimately result in ozone destruction, as they are coated with sulfuric acid,” said Keutsch. “Instead of trying to minimize the reactivity of the aerosol, we wanted a material that is highly reactive but in a way that would avoid ozone destruction.”

An antacid for the stratosphere

In order to keep aerosols from harming the ozone, the particles would need to neutralize sulfuric, nitric, and hydrochloric acid on their surface. To find such a particle, Keutsch turned to his periodic table. After eliminating the toxic elements, the finicky and rare metals, the team was left with the alkali and alkaline Earth metals, which included sodium and calcium carbonate.

“Essentially, we ended up with an antacid for the stratosphere,” said Keutsch.

Through extensive modeling of stratospheric chemistry, the team found that calcite, a constituent of limestone, could counter ozone loss by neutralizing emissions-borne acids in the atmosphere, while also reflecting light and cooling the planet.

Funded by Bill Gates

Grants for research are provided to Harvard University from gifts made by Bill Gates from his personal funds. The activities of the Fund for Innovative Climate and Energy Research fall outside the scope of activities of the Bill & Melinda Gates Foundation.

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