Mitigating the risk of geoengineering: Aerosols could cool the planet without ozone damage

December 12, 2016, Harvard John A. Paulson School of Engineering and Applied Sciences
Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have identified an aerosol for solar geoengineering that may be able to cool the planet while simultaneously repairing ozone damage. Credit: NASA

The planet is warming at an unprecedented rate and reducing emissions of greenhouse gasses alone is not enough to remove the risk.

Last year's historic Paris climate agreement set the goal of keeping global temperatures no higher than 1.5 degrees Celsius above the preindustrial levels. Emission reductions will be central to achieving that goal, but supplemental efforts can further reduce risks

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 . But these sulfate aerosols also carry significant risks. The biggest known risk is that they produce in the stratosphere, which damages . Since the ozone layer absorbs ultraviolet light from the sun, can lead to increased rates skin cancer, eye damage and other adverse consequences.

Now, researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have identified an aerosol for solar geoengineering that may be able to cool the planet while simultaneously repairing ozone damage.

The research is published in the Proceedings of the National Academy of Sciences.

"In solar geoengineering research, introducing sulfuric acid into the atmosphere has been the only idea that had any serious traction until now," said David Keith, the Gordon McKay Professor of Applied Physics at SEAS and Professor of Public Policy at the Harvard Kennedy School and first author of the paper. "This research is a turning point and an important step in analyzing and reducing certain risks of solar geoengineering."

This research fundamentally rethinks what kinds of particles should be used for solar geoengineering, said Frank Keutsch, the Stonington Professor of Engineering and Atmospheric Science at SEAS and Professor of Chemistry and Chemical Biology and coauthor of the paper.

Previous research focused on ways to limit the ozone-damaging reactions produced by nonreactive aerosols. But Keutsch and Keith, along with coauthors Debra Weisenstein and John Dykema, 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 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."

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 handy 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.

"Calcite is one of the most common compounds found in the earth's crust," said Keith. "The amounts that would be used in a solar geoengineering application are small compared to what's found in surface dust,"

The researchers have already begun testing calcite in lab experiments that mimic stratospheric conditions. Keith and Keutsch caution that anything introduced into the atmosphere may have unanticipated consequences.

"Stratospheric chemistry is complicated and we don't understand everything about it," Keith said. "There are ways that this approach could increase global ozone but at the same time, because of the climate dynamics in the polar regions, increase the ozone hole."

The researchers emphasize that even if all the attendant risks could be reduced to acceptable levels, is not a solution to climate change.

"Geoengineering is like taking painkillers," said Keutsch. "When things are really bad, painkillers can help but they don't address the cause of a disease and they may cause more harm than good. We really don't know the effects of geoengineering but that is why we're doing this research."

Explore further: Adjusting Earth's thermostat, with caution

More information: Stratospheric solar geoengineering without ozone loss, PNAS,

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1 / 5 (3) Dec 12, 2016
So, literal chemtrails?
5 / 5 (3) Dec 12, 2016
The main danger of global warming is that higher high temperature events will quickly degrade the Earth's ecosystems. It is obviously impractical to address this danger with only a carbon diet. Therefore SRM (solar radiation management) is not only a good choice, but would prevent a wide catastrophic of melting methane hydrates resulting in the Earth being a much bigger emitter of greenhouse gas than human industry. Soon we will have a clean and cheap source of energy that will be able to remove the excess carbon from the air, but until then we face a planetary catastrophe in terms of global warming feedback loops. What I am saying ought not even be controversial if not for the irrationality of the current discourse on the subject.
2 / 5 (4) Dec 12, 2016
"Stratospheric chemistry is complicated and we don't understand everything about it," Keith said. "There are ways that this approach could increase global ozone but at the same time, because of the climate dynamics in the polar regions, increase the ozone hole."

Oh the AGW Cult. Push the CO2 lies and then truly fuck things up with something they are totally clueless about, geoengineering.
5 / 5 (2) Dec 12, 2016
So, literal chemtrails?

Calcium Carbonate = TumsTrails
1 / 5 (1) Dec 12, 2016
Excellent. A bandaid for metastatic cancer.
2.6 / 5 (5) Dec 12, 2016
Why not just accept that the current trend towards global warming is the natural result of life acquiring a human level of intelligence and technology? We see it now and understand that it needs to be brought under control, but it will take time. instead of lamenting the extinction of some of the other species that have specialized themselves into oblivion, we should be looking forward to the explosion of new species that will eventually result from the increase of available energy in the environment. We, as a species, have shown a remarkable ability to thrive in almost any climate and are in no way threatened by this. Why do the liberals have to be so... controlling and conservative?
1.8 / 5 (5) Dec 12, 2016
It is this go, go, global takeover attitude that drives the "global warming" debate.

If one takes a quick look at the geologic temperature record, one sees that we are still in an ice age.


Even now, everyone can agree that Pollution is a real problem.

If a multi-billion dollar ... multi-national corporation wanted to stop polluting the planet, they would have to get their share holders to agree.

To think that the peasants are responsible for pollution, is false.

To think that we need to stop bbq'ing in the back yard to save the planet, is false.

To think that we need to worry about cow farts, is ridiculous.

To think that we need a multi-billion, multi-national corp to spray chemicals in the air to save the day, is batsh*t crazy.

4.3 / 5 (6) Dec 12, 2016

Geoengineering: Humanity as a whole agreeing to light its farts on fire.
1 / 5 (4) Dec 13, 2016
Sulfur, huh? Anyone remember "acid rain?" Whatsamatter, greenies? Did that scam not make you enough money so you moved on to global warming?
5 / 5 (2) Dec 13, 2016

Agreed. Pumping umpteen billion tons of stuff into the atmosphere without any way to take it back out - what could possibly go wrong?
1 / 5 (4) Dec 13, 2016
A large problem with propaganda is that those who create and spread it begin to believe their own lies. A recent example is the U.S. presidential election where the biased media using biased polls predicted a Democrat win and were shocked when the opposite happened because they believed their own propaganda.

When science is abused in the same manner, you get these outlandish and destructive schemes because of the hysteria from believing in ones own propaganda.

What is really scary is that we may actually implement one or more of these insane schemes. Self delusion has real consequences.
not rated yet Dec 19, 2016
On it's face, ridiculous. How many fewer feet of ocean will support photosynthesis if we "dim" the sun with reflecting sulfates?
not rated yet Dec 19, 2016
Twenty shuttle flights would take up enough mylar balloons to halt global warming instantly

Erm. I think you need to redo those calculations. You're off by a couple of orders of magnitude.
not rated yet Dec 19, 2016
Now all we need to do is make a calcite refrigerant. ! ( and put it in airplane fuel )

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