NASA has released a satellite image that depicts a patchwork of emissions trails over busy shipping lanes in the Atlantic Ocean.
The narrow clouds in the photograph, known as ship tracks, are formed when water vapour condenses around the tiny particles of pollution in ship exhaust. These ship tracks typically form in areas where low-lying stratus and cumulus clouds are present.
NASA’s Moderate Resolution Imaging Spectroradiometer aboard the Aqua satellite captured the image of the waters off Portugal and Spain on 16 January. According to NASA, some of the trails depicted stretch for hundreds of kilometres from end to end. The narrow ends of the clouds are youngest, while the broader portions are older.
Some of the particles generated by large ships, especially sulfates, are water soluble and serve as “seeds” around which cloud droplets form. Clouds infused with ship exhaust have a greater number of smaller droplets than unpolluted clouds.
This means that the light hitting the polluted clouds scatters in multiple directions, making them appear brighter and thicker than unpolluted marine clouds, which are usually seeded by larger, naturally occurring particles such as sea salt.
The presence of a large number of small “seed” particles in ship exhaust is also thought to lead to increased lightning strikes over the world’s most crowded shipping lanes.