In a guarded compound at the foot of the Rockies, government scientists are working on a new kind of global alarm system: One that can detect if another country, or maybe just an adventurous billionaire, tries to dim the sun.

Every few weeks, researchers in Boulder, Colo., release a balloon that rises 17 miles into the sky. Similar balloons are launched with less frequency from sites in Alaska, Hawaii and New Zealand; Reunion Island, near the coast of Africa; and even Antarctica. They make up the building blocks of a system that would alert American scientists to geoengineering.

As the planet continues to heat up, the idea of intentionally trying to block solar radiation — sometimes called solar radiation modification, solar geoengineering, or climate intervention — is gaining attention. Governments, universities, investors and even environmentalists are pouring millions of dollars into research and modeling of geoengineering systems.

It could be a relatively quick way to cool the planet. But it could also unleash untold dangers.

Many worry that solar geoengineering could have unintended consequences, shattering regional weather patterns and damaging everything from agriculture to local economies. And the first steps could be done quietly, by a rogue actor or another nation operating without any regulations or controls.

So the United States is building a system that would allow it to determine if and when others may be trying to tamper with the Earth’s thermostat.

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