Environment

A last-resort ‘planet-hacking’ plan could make Earth habitable for longer — but scientists warn it could have dramatic consequences

One way to prevent the Earth’s temperature from rising into a city-drowning, hurricane-strengthening, heat-stroke–triggering danger zone is to immediately switch from fossil fuels to renewable energy sources.

At the moment, that transition seems unlikely. So scientists and tech innovators are also investigating various forms of geoengineering — an approach that involves transforming the Earth’s clouds and skies in ways that help cool the planet or suck carbon out of the atmosphere.

That idea, however, is extremely controversial. Some researchers believe such work could be a necessary part of the fight against climate change, but others argue that meddling with the planet exposes the world to a host of new risks. Plus, there’s a growing fear that a rogue actor trying to achieve something “good” could attempt one of these globe-altering projects and spark a devastating international conflict.

Two new papers published July 20 in the journal Science investigate two of the most well-studied geoengineering strategies: cirrus cloud modification and injecting sulfur into the atmosphere.

The authors of the papers make clear that these approaches are very risky and far from viability — so much so, in fact, that most researchers hope they never become necessary. But the papers also lay out the reasons why these strategies might work and are worth studying.

Recreating a volcanic eruption
If we delay aggressively cutting greenhouse gas emissions until 2040, authors Ulrike Niemeier and Simone Tilmes write in Science, the global temperature is projected to rise more than 2 degrees Celsius above pre-industrial levels. That is an increase that most scientists agree would create dramatic, irreversible consequences for human civilization and the planet.

The authors pick that as the point at which drastic intervention might be needed in order to stave off disaster. One option in that case would be to mimic a volcanic eruption.

When a volcano erupts, it spews forth lava, gas, and smoke, filling the skies with sulfur. Those clouds of sulfur reflect more of the sun’s solar radiation back into space and away from Earth, which has a cooling effect on the planet.


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Researchers are investigating how this effect could be artificially recreated. The leading proposal involves planes that would inject sulfur into the atmosphere.

Niemeier and Tilmes reviewed the math, and said that in order to counteract the temperature rise at that point, we’d have to inject the atmosphere with the amount of sulfur that was created by the 1991 eruption of Mount Pinatubo every year for 160 years. (For context, the Pinatubo eruption was the second largest of the 20th century.)

This effort, they write, would require 6,700 sulfur-injection flights per day — at a cost of about $20 billion a year.

The authors also note that the technology required for this aerosol modification in the stratosphere doesn’t exist yet, and that their timeline assumes that global carbon emissions would reach zero before 2100.

We’re still far from understanding all the risks involved with injecting sulfur into our atmosphere; however, a major one is the destruction of ozone, the layer that helps keep dangerous ultraviolet radiation from reaching Earth. The sulfur approach would also cool land more than oceans, which would continue to change and acidify. And it would transform tropical monsoons, reducing rainfall and potentially causing droughts in places like India.

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