Harvard scientists are poised to conduct the first sun-dimming experiment.

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At a Glance

Sun-dimming is a geoengineering techniquethat researchers hope will help mitigate global warming.Calcium carbonate, the common ingredient in antacid, will be launched into the stratosphere.

A team of Harvard scientists is poised to conduct the firstsun-dimming experiment in early 2019, a geoengineering techniquethat researchers hope will help keep global warming at bay.

The $3 million (SCoPEx) entails the launch of two steerable balloons filled with calcium carbonate, the common ingredient in antacid.

Once the balloons reachthe stratosphere — the atmospheric layer that stretches from about 6 to 31 miles above Earth's surface — small plumes of the will be released, according to Nature Magazine. Ironically, the plumes will be about the size of a bottle of antacid. The balloons will then collect data on how the calcium carbonate interacts with the stratosphere.

The theory is that the calcium carbonate, which occurs naturally in chalk, will reflect some of the sun's rays back into space,cooling the planet.

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Many environmental groups are opposed to solar geoengineering, noting that it is a distraction away from the "onlypermanent solution to climate change: reducing greenhouse gas emissions."

The Harvardnotes on its website that "solar geoengineering,in particular,could not be a replacement for reducing emissions (mitigation) or coping with a changing climate (adaptation); yet, it could supplement these efforts."

Zhen Dai, a Harvard University doctoral candidate working at the university's Solar Geoengineering Research Program, tried to calm the trepidations expressed by those who believe releasing anything into the atmosphere is a dangerous precedent.

“I’m studying a chemical substance,” she said. “It’s not like it’s a nuclear bomb.”

Jim Thomas, co-executive director of the ETC (Erosion, Technology andConcentration) Group, a Montreal, Canada, environmental advocacy organization that opposes geoengineering, says the project is "as much an experiment in changing social norms and crossing a line as it is a science experiment."

The stratosphere was chosenbecause particles released there can spread around the globe and remain in thelayer for up to two years. The thinking behind the theory is thatif small particles of calcium carbonate are placed"strategically and regularly in both hemispheres, they will create a relatively uniform blanket that would shield the entire planet" from the heating effects of the sun, Nature Magazine noted.

The cost of any long-term plan to usegeoengineering techniques being explored to cool the planet would be considerable. Last year, the Intergovernmental Panel on Climate Change said a fleet of high-flying aircraft could deposit enough sulfur dioxide to mitigate roughly for about $1 billion to $10 billion per year.

Sulfur dioxide,released by volcanoes, is another substance that has been widely studied in the lab as a possible compound for solar geoengineering. There have been some qualms over the use of the sulfur compound in light of impacts observed after the second-largest volcanic eruption of the 20th century occurred at Mount Pinatubo in the Philippines.

The U.S. Geological Survey says sulfur dioxide released during the 1991 eruption sent 20 million tons of sulfur dioxide into the stratosphere, creating a haze that cooled the planet by for around 18 months. However, other observed outcomes linked to the eruption included an increased rate at whichthe ozone layer was depleted.

Some scientistsbelieve sulfate aerosols warmed by the sun in the stratosphere may affect the movement of the jet stream, which could significantly impact weather patterns.

“There are all of these downstream effects that we don’t fully understand,” Frank Keutsch, an atmospheric chemist at Harvard and SCoPEx’s principal investigator, noted in the Nature Magazine article.

The Harvard team chose to use calcium carbonate because, theoretically, aerosols from the compound won't heat up as much as sulfates.

Keutsch sees that as a potential problem because while sulfates have been observed and studied in the atmosphere following volcanic eruptions, there have been no studies or observations on the impact of calcium dioxide on the stratosphere. That's where the Harvard experimentmight shed some new light.

"We actually don’t know what it would do, because it doesn’t exist in the stratosphere," Keutsch says. "That sets up a red flag."

Still, the project's website notes that the "test will pose to people or the environment."

"Calcium carbonate is a nontoxic chemical commonly found in nature, for example as limestone, and sub-micron precipitated calcium carbonate particles like the ones we will useare a common additive to consumer products such as paper and toothpaste," according to the website.

Italso notes that the amount of calcium carbonate to be dispersed in the stratosphere for the experiment will be "very small compared to other routine releases of material into the stratosphere by aircraft, rocketsor routine balloon flights."

Harvard experimental physicist David Keith, who partneredwith Harvard atmospheric chemist James Anderson for the experiment, said there has been no public outcry or protestsover the planned experiment, adding that the benefits of solar geoengineering could far outweigh the potential negative impacts.

“Despite all of the concerns, we can’t find any areas that would be definitely worse off,” Keith said. “If solar geoengineering is as good as what is shown in these models, it would be crazy not to take it seriously.”