Stopping geoengineering, by accident

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Sep 14, 2023

Scientists discuss unintentional geoengineering caused by maritime shipping emissions, which brighten clouds and reflect solar radiation. Regulations to cut sulfur emissions unintentionally warmed the surface of the oceans. The podcast explores the mechanism behind marine cloud brightening, the impact on global temperatures, and the unintended consequences of International Maritime Organization regulations. It also highlights the need for global conversations about geoengineering and further research on regional effects.

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INSIGHT

Accidental Geoengineering

Shipping emissions inadvertently geoengineered the planet by releasing sulfur dioxide, which brightened clouds and reflected sunlight.
The IMO's 2020 regulations to reduce sulfur emissions effectively stopped this unintentional geoengineering experiment.

INSIGHT

North Atlantic Susceptibility

The North Atlantic is particularly susceptible to cloud brightening from aerosols due to its flat terrain and prevailing winds.
It also has a naturally low albedo, making cloud brightening's cooling effect more pronounced.

INSIGHT

Sulfate Aerosols: Volcanoes vs. Ships

Volcanoes and ships both emit sulfate aerosols, but their impact differs based on where they're released in the atmosphere.
Volcanic sulfates reach the stratosphere, having a direct cooling effect, while ship emissions primarily brighten clouds in the lower atmosphere.

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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 accidentally warmed the surface of the oceans.

So how big of a deal is this?

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

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, like heat waves and hurricanes
What this accidental experiment tells us about how someone could conduct a deliberate geoengineering experiment

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