As the world races against time to tackle climate change, most of the solutions we have—like renewable energy and reducing carbon emissions—are long-term goals. The problem is, we may not have the luxury of waiting years for their effects. According to the Intergovernmental Panel on Climate Change, global temperatures could rise above the crucial 1.5°C threshold as early as this decade.

Remember 2023, the year of record-breaking heatwaves, forest fires, and floods. Well, 2023 was also the year when for the first time Earth’s average temperature stayed above 1.5 °C for almost one-third of the year. Now imagine what would happen if our planet’s temperature remains above the 1.5 °C mark permanently.

This is why, in addition to the ongoing efforts, we also need strategies that could allow us to cool down Earth in a short time frame. A new study suggests one radical idea: shooting diamond nanoparticles into the stratosphere (9 to 50 km above the surface) to reflect sunlight and reduce global temperatures in a matter of months.

The magic of diamonds in the stratosphere

The idea of cooling Earth with particles isn’t new. It’s based on a technique called Stratospheric Aerosol Injection (SAI), first proposed in 1974 by climate scientist Mikhail Ivanovich Budyko. SAI involves injecting small particles into the upper atmosphere. By injecting tiny particles into the upper atmosphere, scientists could reflect sunlight back into space, lowering the amount of heat reaching Earth’s surface.

“The natural analogs of SAI are large explosive volcanic eruptions, which emit large amounts of sulfur into the stratosphere. An example is the 1991 Mt. Pinatubo eruption, which cooled the global climate by about 0.5 degrees Celsius during the years following the eruption,” Sandro Vattioni, lead study author and an expert in atmospheric physics at ETH Zurich, told ZME Science.  

Until now, most research on SAI has focused on the injection of sulfur. However, sulfur geoengineering has its drawbacks, including contributing to the depletion of the stratospheric ozone layer. Vattioni and his team suggest a better alternative: diamond nanoparticles. Diamonds, they found, could reflect sunlight without causing the harmful side effects associated with sulfur.

“In our work, we showed that the use of other particle types with favorable optical properties such as alumina, calcite, or diamond particles could substantially reduce the adverse side effects that occur when injecting sulfur,” Vattioni added.

The researchers propose injecting tiny diamond particles no larger than 150 nanometers into the stratosphere using high-altitude aircraft. They ran a simulation to test the effectiveness of their proposed method.

The results of the simulations revealed various benefits of using diamond nanoparticles for SAI. For instance, unlike sulfur, diamond particles are inert, meaning they don’t interact with ozone. Compared to sulfur, diamond only absorbs very little radiation.

This would substantially reduce the local heating in the stratosphere —- a drawback of sulfuric acid aerosols that results in warming at the local level as these aerosols often trap heat in a specific area of the atmosphere.

But aren’t diamonds expensive?

The idea of shooting diamonds in the sky may sound romantic but there’s a catch. The study authors didn’t calculate the exact cost of injecting diamonds but they estimate that it may require billions or maybe even trillions of dollars. 

Moreover, diamond nanoparticles once injected aren’t going to stay forever in the sky. They will eventually fall down to earth although very slowly since they are so small (about 5-10 km/yr). Therefore, we would need to inject diamonds not just once but regularly, making it a highly capital-intensive process.  

Fortunately, diamonds aren’t the only option. The study also looked at more affordable materials, like calcite and alumina, which showed promise as effective alternatives.

“Calcite particles for example are another particle type we investigated, which performed similarly well in terms of reducing stratospheric warming. They would cost significantly less. Many mountains across the world are made of limestone, which is made of calcite. Another good option would be alumina particles,” Vattioni told ZME Science.  

As the planet inches closer to the 1.5°C threshold, innovative ideas like SAI could be crucial for rapidly cooling the Earth. While challenges remain, this research gives scientists a new tool to fight climate change—and perhaps buy us some much-needed time.

The study is published in the journal Geophysical Research Letters.