If you have a habit of viewing satellite images of the world’s oceans – and who doesn’t? – maybe you’re lucky and see long, thin clouds, like white stripes over the sea. In some regions, such as off the west coast of the United States, the slashes can intersect, creating huge hash marks. That is a peculiar phenomenon known as a ship track.
As cargo ships churn along and fling sulfur into the atmosphere, they’re actually tracking their routes for satellites to see. That’s because those pollutants ascend to low clouds and fill them in by acting as nuclei that attract water vapor. who also brightens up the clouds. Counterintuitively, these pollution-derived spores actually have a cooling effect on the climate, as brighter clouds bounce more of the sun’s energy back into space.
The Pacific Ocean off California is particularly marked because there is a lot of shipping along that coast and ideal atmospheric conditions for the formation of the tracks. Well, at least it is used to be. In 2020, a regulation of the International Maritime Organization (IMO) came into force that: the amount of sulfur is severely limited ships can spit. Shipping companies switched to low-sulphur fuel, which improved air quality, especially around busy ports. But by doing so, they reduced the number of ship tracks, which means fewer glowing clouds and therefore more warming.
Friday writing in the news scientific progress, researchers described how they used a new machine learning technique to quantify the clouds better than ever, showing how the sulfur control halved the number of ship tracks across major shipping routes. That, in turn, has had a moderate warming effect on those regions.
“The big finding is that by 2020 the regulation proposed by the IMO has reduced global ship track numbers to the lowest point on record,” said Tianle Yuan, a climate scientist at NASA and the University of Maryland who led the study. . (Yes, reduced economic activity during the pandemic lockdowns may also have had a small impact. But rail activity has remained low even as freight traffic picked up again.), and we’re seeing that impact,” he continues. “But there the effect is not global.”
In Europe and North America, for example, officials had already delineated the so-called emission control areas, or ECAs, which set local versions of the standards of the 2020 global rule. “The number of tracks within the ECAs, within the control zones, decreased drastically, to the point of almost disappearing,” Yuan says. “But Outside we actually saw some increase because the shipping routes had shifted.”
The satellite images caught ships doing something secretly. Outside the control zones, where the ships were not bound by sulfur regulations, they burned ordinary old fuel. Once inside an ECA, their operators were able to switch to low-sulphur fuel, in compliance with pollution regulations. (Sulphur is a normal constituent of a fossil fuel and requires additional processing to remove it. Because low sulfur fuel is more expensive, it is more cost effective for ship operators to spend as much time as possible outside the ECAs, burning the old stuff .)