“Ship tracks” clouds to record-low levels in 2020

Traffic & Weather

**** Info via Environment Canada

“Ship tracks” clouds to record-low levels in 2020

Have you ever heard of “ship tracks”? Ship tracks form when water vapour condenses around tiny particles of pollution that ships emit as engine exhaust, and they are visible from space. Observed over shipping lanes around the globe, ship tracks typically form in areas where low-lying stratus and cumulus clouds are present.

Satellite image showing ship tracks off the Pacific coast of North America on December 7, 2021. Credit: NASA Earth Observatory.

Ship tracks were first observed by weather satellite images in the 1960s, and since then, studies have used such observations to better understand aerosol-cloud interactions and their effect on climate.

In 2020, the International Maritime Organization (IMO) implemented a new global standard limiting sulphur content in fuel, hoping to reduce pollution associated with ship exhaust. Sulphur oxides from shipping are harmful to human health, causing respiratory, cardiovascular and lung disease, especially in coastal regions, as well as acid rain, which affects crops and the environment. By capping fuel sulphur content to 0.5 percent from 3.5 %, the IMO’s new global regulation changed ship exhaust’s chemical and physical composition. Fewer sulphur emissions mean fewer sulphate aerosol particles able to contribute to the formation of detectable ship tracks.

And the good news is that it seems to have worked! After analyzing the 2020 data, NASA researchers found that ship-track density fell that year in every major shipping lane, as shown below:

Anomaly (difference from normal) of ship tracks density around the world. Violet means less sulphur pollution. Credit: NASA Earth Observatory.

Even though the COVID-19 pandemic played a role in decreasing global shipping traffic by 1.4 % for a few months in 2020, this change alone could not explain the significant decrease in observed ship tracks. Ship-tracking data remained low for several months through 2021. Based on this, the researchers concluded that the new global fuel regulation played a significant part in reducing ship tracks, which is promising for the future.


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