Ships now spew less sulfur, but ‘warming has sped up’

Cloud formation [image credit:NASA]

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It looks like geo-engineering in reverse. We read: ‘Where the cloud count was down, the degree of warming was generally up.’ Surely anything else would have been a surprise. Near the end of the article we read: ‘But lots of uncertainties remain’. Indeed, that’s how it usually is with clouds.
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New findings document fewer ship tracks, reduced cloud cover, and boosted warming after ship emissions regulations took effect in 2020, says Science Daily.

Last year marked Earth’s warmest year on record. A new study finds that some of 2023’s record warmth, nearly 20 percent, likely came as a result of reduced sulfur emissions from the shipping industry. Much of this warming concentrated over the northern hemisphere.

The work, led by scientists at the Department of Energy’s Pacific Northwest National Laboratory, published [this week] in the journal Geophysical Research Letters.

Regulations put into effect in 2020 by the International Maritime Organization required a roughly 80 percent reduction in the sulfur content of shipping fuel used globally. That reduction meant fewer sulfur aerosols flowed into Earth’s atmosphere.

When ships burn fuel, sulfur dioxide flows into the atmosphere. Energized by sunlight, chemical intermingling in the atmosphere can spur the formation of sulfur aerosols. Sulfur emissions, a form of pollution, can cause acid rain. The change was made to improve air quality around ports.

In addition, water likes to condense on these tiny sulfate particles, ultimately forming linear clouds known as ship tracks, which tend to concentrate along maritime shipping routes. Sulfate can also contribute to forming other clouds after a ship has passed. Because of their brightness, these clouds are uniquely capable of cooling Earth’s surface by reflecting sunlight.

The authors used a machine learning approach to scan over a million satellite images and quantify the declining count of ship tracks, estimating a 25 to 50 percent reduction in visible tracks. Where the cloud count was down, the degree of warming was generally up.
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The work also illustrates that real-world changes in temperature may result from changing ocean clouds, either incidentally with sulfur associated with ship exhaust, or with a deliberate climate intervention by adding aerosols back over the ocean.

But lots of uncertainties remain. Better access to ship position and detailed emissions data, along with modeling that better captures potential feedback from the ocean, could help strengthen our understanding.

Full article here.
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Image: Cloud formation [credit: NASA]