men watching sunrise

Solar geoengineering is potentially a powerful tool to fight climate change. It’s also rife with controversy.

  • Mexico has banned solar geoengineering experiments after a startup sent sulfur dioxide into the stratosphere.
  • Solar geoengineering aims to make Earth’s atmosphere a more effective solar reflector.
  • We don’t even know if solar geoengineering is a good idea, but the White House is currently assessing how we can alter our atmosphere and cool the planet.

On June 15, 1991, Mount Pinatubo—located in the Luzon Volcanic Arc in the Philippines— erupted and sent ash 28 miles skyward in a plume some 1.2 cubic miles in size. It was the second largest volcanic eruption in the 20th century (taking the silver behind a 1912 eruption in Alaska), and the sudden injection of sulfur dioxide (SO2) aerosols from Pinatubo also wrought unforeseen consequences for the climate.

Because of these light-reflecting aerosols, scientists estimate that Earth cooled by 1 degree Fahrenheit over the next 15 months. Today, Pinatubo remains one of the largest solar geoengineering experiments in living memory.

As Earth continues to warm thanks to human-induced climate change, the natural cooling effects of volcanoes, and more specifically, the SO2 aerosols they produce, has scientists intrigued by their possible artificial applications. So much so that in November 2022, the Biden Administration put together a five-year study to understand its benefits and risks.

But not all countries are quite so gung-ho.

In late 2022, the startup Make Sunsets announced that it was injecting small amounts of aerosols into the stratosphere as an experiment in solar geoengineering. The company released two weather balloons from Baja California that were filled with less than 10 grams of SO2 each—not exactly Pinatubo levels. But last week, the Mexican government banned the controversial deployment of any solar geoengineering efforts, citing a 2010 moratorium developed at a United Nations conference on biodiversity. Make Sunsets is already selling “cooling credits” at $10 per gram of SO2, a similar business model to the also controversial carbon offsets.

Mexico (and the rest of the world) has reason to worry about solar geoengineering. Although its effectiveness, as seen in Pinatubo but also other global cooling periods in the distant past, can’t be debated, the potential side effects of intentionally pumping the stratosphere with SO2 are disastrous.

For one, scientists think that over time, the skies would transform from blue to white while sunsets would become dazzlingly bright (as volcanoes tend to do). Sulfur dioxide is also the same stuff pumping from power plants around the world, and this kind of geoengineering would likely induce the usual bevy of bad side effects, like ozone depletion, acid rain, and respiratory illness.

In other words, caution seems wise as governments and environmentalists figure out how to cure the illness without killing the patient. After all, any solar geoengineering plan would inevitably impact the entire planet. While Make Sunsets draws ire from the Mexican government, many scientists are also perturbed, telling MIT Technology Review that it’s way too early in the game to know if aerosol injection is even a good idea—let alone trying to make a buck off of it.

For now, one nation has put the kibosh on plans to geoengineer the planet, but this controversial science isn’t going away any time soon.

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