Putting a halt to geoengineering — by accident

On the Catalyst with Shayle Kann podcast this week:

Solar geoengineering is a hot (er, cool?) topic these days. One method involves injecting a form of sulfur into the atmosphere to reflect solar radiation and help reduce global temperatures. But it could also cause unpredictable changes to ozone, rainfall and ecosystems. So when a rogue startup began sending balloons of sulfur dioxide into the atmosphere earlier this year, it sparked outrage.

But here’s the thing: We’ve been geoengineering our atmosphere for decades, just not intentionally. Scientists have long known that sulfur-dioxide emissions from maritime shipping have a cooling effect on the atmosphere. They brighten clouds and reflect more solar radiation. We’ve also known that sulfur dioxide is a toxic air pollutant that causes tens of thousands of premature deaths per year. 

So in 2020, when the International Maritime Organization, which regulates shipping, required ships to drastically cut their sulfur-dioxide emissions, it reduced air pollution. But it also unintentionally warmed the surface of the oceans.

How big of a deal is this?

In this episode, Shayle talks to Dan Visioni, a climate scientist and assistant professor at Cornell University’s Department of Earth and Atmospheric Sciences. They cover topics including

• The mechanism behind marine cloud brightening and how it differs from stratospheric sulfate injection.
• Why the warming effect was so strong in the North Atlantic in particular.
• What we still don’t understand about the impact on global mean temperatures and regional weather, such as heat waves and hurricanes.
• What this accidental experiment teaches us about how to conduct a deliberate geoengineering experiment.

Recommended resources:

• Carbon Brief: How low-sulphur shipping rules are affecting global warming

• Atmospheric Chemistry and Physics: Climate and air quality trade-offs in altering ship fuel sulfur content

Catalyst is a co-production of Post Script Media and Canary Media.

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