Big vessels spew sulfur, which brightens clouds to produce long “ship tracks.” These emissions cause environmental damage—but also help cool the planet, reports Wired.
New technique to quantify the clouds
Writing Friday in the journal Science Advances, researchers described how they used a new machine-learning technique to quantify the clouds better than ever before, showing how the sulfur regulation cut the amount of ship tracks over major shipping lanes in half. That, in turn, has had a moderate warming effect on those regions.
“The big finding is the regulation in 2020, put forward by the IMO, has reduced the global ship-track numbers to the lowest point on the record,” says Tianle Yuan, a climate scientist at NASA and the University of Maryland, who led the research. (Yes, reduced economic activity during the pandemic lockdowns may have had a small influence too. But ship-track activity has remained low even as cargo traffic has picked back up.)
“We’ve had similar but smaller-scale, strict regulations before, and we can also see that impact,” he continues. “But there, the effect is not global.”
Use of clean fuel?
In Europe and North America, for instance, officials had already sectioned off what are known as emission control areas, or ECAs, which established local versions of the standards set by the 2020 global rule. “The number of tracks within the ECAs, within the control zones, reduced dramatically, to the point of almost disappearing,” Yuan says. “But outside of it, actually we saw some increase because the shipping routes had shifted.”
The satellite imagery caught ships doing something sneaky. Outside of control zones, where the vessels weren’t bound by sulfur regulations, they burned regular old fuel. Then once inside an ECA, their operators could switch to low-sulfur fuel, coming in line with the pollution rules. (Sulfur is a normal component of a fossil fuel, and it takes extra processing to remove it. Because low-sulfur fuel is more expensive, it’s more cost-effective for ship operators to spend as much time outside of ECAs as possible, burning the old stuff.)
“Our technique can help to validate whether a ship is using clean fuel or not,” says Yuan, “because we can observe indirectly how much pollution they’re putting into the air.”
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