Project To Cool Earth By Dimming The Sun Poised For Groundbreaking Test Run


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The latest UN State of the Climate report spells it out clearly. The last four years have been the hottest on record and the Earth is on track to keep warming. All the available evidence points toward an unstable future characterized by more extreme weather events as well as increased desertification of dry regions and exacerbated rainfall in wet regions. Our health, food security, infrastructure, and economic productivity will all be impacted, and numerous plant and animal species will likely go extinct.  

So, what can we do? One idea that has been kicked around for decades, yet has never gotten off the ground, is called solar geoengineering. Elegant in its simplicity, the idea is to cool Earth by introducing a plume of sunlight-reflecting small molecules into the upper atmosphere.


We know from observing the temporary climate cooling that follows volcanic eruptions – which launch large quantities of sulfur dioxide into the stratosphere – that the concept is sound, but solar geoengineering has not been attempted yet because of all of the things that could go wrong. For example, what if the molecules further degrade the ozone layer? What if the sunlight shielding is too extreme in one area?  

But desperate times call for bold science. And now, a Harvard University solar geoengineering project dubbed the Stratospheric Controlled Perturbation Experiment (SCoPEx) is nearing the home stretch toward its first trial launch.

An illustration of an earlier, 2014 concept model of the propeller-driven SCoPEx system. The stream emanating from the Stratocruiser is the aerosolized particles, and the device lowered down into the stream in panel c contains sensors to monitor the particles. Dykema et al. / Philosophical Transactions of the Royal Society A, 2014

The brainchild of atmospheric chemists James Anderson and Frank Keutsch and experimental physicist David Keith, SCoPEx will take the form of a propelled balloon carrying a particle dispenser and a suite of chemical, temperature, and light sensors. According to a report in Nature, the initial tests will involve two steerable balloons each spraying about 100 grams (3.5 ounces) of calcium carbonate into the air 20 kilometers (12 miles) above the American Southwest. Once the calcium carbonate is deployed, the balloon will fly into the heart of the plume so that the sensors can monitor how the molecules, which do not occur naturally in the atmosphere, behave in this environment.

If all goes to plan, the experiment could proceed in the first half of 2019. In the meantime, the trio’s teams are working to coordinate the final stages of development of the various instruments and balloons, most of which are being made by specialist manufacturers.


By their calculations, a moderately sized fleet of balloons dispensing 0.5-micrometer calcium carbonate crystals could improve the climate of regions around the world.

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

That being said, the group understand the gravity of trying to launch a project that could impact the entire planet. To move forward as responsibly as possible, the scientists are assembling an independent advisory committee who will review the plans before SCoPEx launches.

“Getting it done right is far more important than getting it done quickly,” Peter Frumhoff, chief climate scientist at the Union of Concerned Scientists and member of the advisory committee selection panel, told Nature. 


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  • global warming,

  • solar geoengineering