More God-Complex Geo-Engineering

Sunscreen in the Sky? Reflective Particles May Combat Warming

Titanium dioxide could scatter sunlight and cool Earth, scientist says.

Ker Than

for National Geographic News

Published May 29, 2012

Spritzing a sunscreen ingredient into the stratosphere could help counteract the effects of global warming, according to scientists behind an ambitious new geoengineering project.

The plan involves using high-altitude balloons to disperse millions of tons of titanium dioxide—a nontoxic chemical found in sunscreen as well as in paints, inks, and even food.

Once in the atmosphere, the particles would spread around the planet and reflect some of the sun’s rays back into space.

About three million tons of titanium dioxide—spread into a layer around a millionth of a millimeter thick—would be enough to offset the warming effects caused by a doubling of today’s atmospheric carbon dioxide levels, according to project leader and chemical engineer Peter Davidson.

(Related: “‘Ice Shield’ Experiment Aims to Cool Mongolian City.”)

The idea was inspired by the 1991 eruption of Mount Pinatubo, a volcano in the Philippines, said Davidson, head of the U.K. consulting firm Davidson Technology.

That eruption spewed 20 million tons of sulfur dioxide into the stratosphere, which formed a fine mist of sulfuric acid that reduced global temperatures by about a quarter of a degree Fahrenheit (half a degree Celsius) for two years.

But sulfuric acid degrades the ozone layer and may trigger droughts, because it absorbs as well as scatters light, lowering temperatures enough to possibly disrupt circulation in the stratosphere, Davidson said.

By contrast, titanium dioxide is seven times more effective at scattering light. That means much less would be needed to achieve the desired effects, he said, and so “there will be a much lower impact on atmospheric circulation.”

Pump Up the Slurry

For Davidson’s project, a slurry containing titanium dioxide would be pumped skyward via flexible pipes, which would be hoisted aboard unmanned balloons flying about 12 miles (20 kilometers) high. A “hypersonic nozzle” would then spray the slurry as fine particles into Earth’s upper atmosphere.

The balloons would be launched from ships or islands located in equatorial regions where storms are infrequent, to reduce the risk of lightning strikes and strong winds damaging the balloons, Davidson said.

Other people have proposed similar projects to cool Earth by intentionally scattering particles high in the air. (See “Extreme Global Warming Fix Proposed: Fill the Skies With Sulfur.”)

What’s new about Davidson’s plan is the use of titanium dioxide and the balloon-dispersal system, which could make the effort cheaper than using previously suggested aircraft or rockets, said Rob Jackson, an environmental scientist at Duke University in North Carolina.

In any particle-dispersion system, “the biggest expense is getting the chemical up into the stratosphere,” said Jackson, who is not involved in the new project.

And if such a project is deployed, it will need to be kept running for as long as atmospheric concentrations of greenhouse gases, such as carbon dioxide, remain high.

“We have to keep doing this until we go carbon negative,” Jackson said. Considering the rate at which greenhouse gas emissions are being reduced, “we could be in this business for centuries.”

Project leader Davidson estimates that his balloon dispersal system would cost between U.S. $800 million and $950 million a year, plus $2 billion to $3 billion annually for the titanium dioxide.

(Related: “Auroras Pictured in HD From High-Flying Balloons.”)

Risks of Spraying Still Uncertain?

Davidson adds that the environmental impacts of spraying titanium dioxide would be minimal.

And “many tests on exposure to titanium dioxide dusts have been done,” he said in an email. “No evidence has been found for health hazards that I am aware of, and at these minute concentrations, issues are most unlikely.”

Still, history has shown that “anytime we’ve injected chemicals into the atmosphere, we’ve been surprised by the chemistry that results,” Duke’s Jackson said.

(Also see “Swimmers’ Sunscreen Killing Off Coral.”)

Chlorofluorocarbons, or CFCs, are prime examples, he said. Those chemicals were widely used as refrigerants and propellants during the 20th century, and they spread through Earth’s atmosphere.

But CFCs were eventually phased out due to their unforeseen harmful effects on the ozone layer. (Related: “First North Pole Ozone Hole Forming?”)

Particle Plan an Insurance Policy

Both Davidson and Jackson say that it will likely be several decades before the titanium dioxide spraying could be safely enacted.

“We shouldn’t, in my view, be doing it at large scales until we know a lot more about it,” Jackson said. “And perhaps we shouldn’t be doing it at all.”

Some scientists worry, for instance, that geoengineering solutions such as chemical dispersal could distract from the real problem: increasing greenhouse gas emissions.

“If policy makers see an easy fix, they might be less likely to do the hard work,” Jackson said. “I don’t want to see us whitewash this problem, and I think that’s what this scheme could do.”

Project leader Davidson argues that humanity needs an insurance policy against the possible catastrophic effects of global warming.

(Also see “Five Last-Ditch Schemes to Avert Warming Disaster.”)

“It would be short-sighted,” he said, “to put off research of such a safety device—like trying to develop a life jacket when you’re swept out to sea and struggling in the water.”

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