The world is unlikely to hit the targets necessary to avoid catastrophic levels of climate change.

Some think that as a last resort, we may need to temporarily cool the planet by modifying the skies. It wouldn’t solve the problem, but it might buy us time.

This technology, called solar geoengineering, is so controversial that some experts think it could lead to global war.

But just in case, a team of researchers at Harvard is planning to conduct one of the first outdoor geoengineering experiments.

It’s 2055. A row of airplanes streak across the sky. They’re barely visible because they’re flying far above the usual traffic of jetliners, transport balloons, and delivery drones.

The mission is to release a cloud of tiny particles into the atmosphere. The cloud creates a barrier that reflects sunlight back into space, keeping it from being absorbed on Earth, where it would further warm the planet.

The planes do this every day, as they have for years.

They’re effective. Because of these planes, there are fewer killer heat waves. Some reports say ice loss at the poles has slowed. There are side effects of altering the atmosphere. Massive droughts have caused famines, and some worry the same technology could be used as a weapon.

That scene, which describes geoengineering, isn’t happening today, contrary to what some conspiracy theorists might tell you. But it soon might. Some scientists think geoengineering could be our last resort to prevent the most catastrophic effects of climate change.

As far out as it sounds, we’ve already seen a lesser form of related experiments with cloud seeding — a way to make it rain by dropping silver ions into the atmosphere — by governments in China and the United Arab Emirates. But the much larger-scale modification of the atmosphere is being worked on already.

This year, a team of scientists at Harvard is hoping to launch what will be the first engineering test flight for one of the first outdoor sky-modifying geoengineering experiments. They know the technology is so risky it might never be safe enough to use, and there are major ethical considerations about who gets to decide what part of the planet gets this treatment, because the effects would be global.

What they discover could one day change the course of planetary history.