Sprinkling diamond dust into the atmosphere could offset almost all the warming caused by humans since the industrial revolution and "buy us some time" with climate change, scientists say.
New research indicates that shooting 5.5 million tons (5 million metric tons) of diamond dust into the stratosphere every year could cool the planet by 1.8 degrees Fahrenheit (1 degree Celsius) thanks to the gems' reflective properties. This extent of cooling would go a long way to limiting global warming that began in the second half of the 19th century and now amounts to about 2.45 F (1.36 C), according to NASA.
The research contributes to a field of geoengineering that's looking for ways to fight climate change by reducing the amount of energy reaching Earth from the sun.
"It's a very controversial topic," study co-author Sandro Vattioni, a researcher in experimental atmospheric physics at the Swiss Federal Institute of Technology in Zurich (ETH Zurich), told Live Science. "There are many scientists who want to forbid doing research — even research — on the topic."
To mitigate the sun's warming effect, researchers have long suggested using tiny particles, or aerosols, that reflect the sun's rays back into space. Injecting these aerosols into the stratosphere — the layer of Earth's atmosphere that sits between 7.5 and 31 miles (12 to 50 kilometers) above the planet's surface — means they will stay in the atmosphere for at least one year before falling back to Earth, the researchers say.
Stratospheric aerosol injection (SAI) takes inspiration from cooling that sometimes takes place after large volcanic eruptions. Volcanoes eject huge clouds of sulfur dioxide. This gas is converted into sulfuric acid in the stratosphere, then condenses to form fine sulfate aerosols that reflect sunlight back to space — preventing it from reaching Earth and warming the planet.
Previous research has explored the plausibility of pumping sulfur dioxide into the stratosphere to combat climate change, but there are several undesirable side effects to consider, Vattioni said. Sulfuric acid aerosols absorb a considerable amount of solar and terrestrial heat, meaning they could trigger warming in the stratosphere that may affect the winds that circulate within it. Any perturbations could then ripple through the troposphere — the layer of the atmosphere below the stratosphere and above Earth's surface — causing disruptions in global precipitation patterns and circulation, he said.
This is where diamonds could come in handy, Vattioni said.
In a modeling study published in October, he and colleagues found that diamond particles would cause neither stratospheric warming nor any other notable disruptions. That's because diamond powder is extremely reflective and doesn't clump together, which is the reason why some other materials absorb heat instead of sending it back to space.
A few hundred high-altitude aircraft would need to fly around Earth emitting particles constantly to reach the amount required for cooling, Vattioni said, but such considerations were beyond the scope of the study.
"We just looked at diamonds and we didn't think about costs or how these particles could be mined," he said. "But obviously these are also questions that need to be considered [to determine] if it's feasible or not to do something like this."
In a new study, published Monday (Dec. 16) in the journal Environmental Research: Climate, the researchers confirmed that diamonds are, theoretically at least, the best material for stratospheric injection.
The team compared the cooling efficiency of diamond particles with that of aluminum and calcite particles using an Earth system model that simulates the full climate response of an intervention. They found that the quantity of diamond dust needed to cool the planet by 1.8 F — 5.5 million tons per year — was about one-third the amount of other materials needed to achieve the same cooling effect.
But the costs and energy demands of these different materials remain unclear. A 2020 study estimated that SAI with sulfur dioxide from 2035 through 2100 would cost $18 billion per year, and the cost for aluminum and calcite is likely to be in the same ballpark, Vattioni said. The bill for diamonds would be much higher, with the 2020 study calculating a total cost over 65 years of $175 trillion.
"In this respect, calcite particles might be a better option," Vattioni said, adding that calcite is a major component in limestone, and therefore easily found in huge quantities across the world.
There are enormous uncertainties around SAI, and scientists are nowhere near implementing it. Some experts are opposed to conducting this type of research at all due to the unforeseen consequences it may have, and because they say it siphons funding away from other climate research.
But "not doing this research would also be to look away from a potential technology that could at least help to mitigate some risks," Vattioni said.
SAI and other geoengineering strategies are not solutions to climate change, but they "could buy us some time," Vattioni said.
"We really run the danger of passing some irreversible climate tipping points and ecological tipping points, and SAI could potentially help to avoid passing these tipping points until we have reached the net zero goal," he said.
