Global Reduction in Ship-tracks from Sulfur Regulations for Shipping Fuel

TL;DR

This study uses deep learning on satellite data to map global ship-tracks, revealing how fuel regulations and global events like COVID-19 significantly impact ship-track frequency and aerosol forcing.

Contribution

First multi-year global climatology map of ship-tracks created using deep learning, linking ship emissions, cloud interactions, and fuel regulations.

Findings

Ship-tracks are over 10 times more frequent than previously estimated.

Fuel regulations and COVID-19 significantly reduced ship-track frequency.

Estimated aerosol indirect forcing ranges from 0.02 to 0.22 W/m².

Abstract

Ship-tracks are produced by ship-emitted aerosols interacting with marine low clouds. Here we apply deep learning models on satellite data to produce the first multi-year global climatology map of ship-tracks. We show that ship-tracks are at the nexus of cloud physics, maritime shipping, and fuel regulation. Our map captures major shipping lanes while missing others, reflecting the influences of background cloud and aerosol properties. Ship-track frequency is more than 10 times higher than expected from a previous survey. Interannual fluctuations in ship-track frequency reflect variations in cross-ocean trade, shipping activity, and fuel regulations. Fuel regulation can alter both detected ship-track density and pattern of shipping routes due to cost economics. The new fuel regulation, together with the COVID-19 pandemic, reduced ship-track frequency in 2020 to its lowest level in recent decades across the globe and may have ushered in a new era of low ship-track frequency. We estimate the aerosol indirect forcing induced by the fuel regulation to be between 0.02 and 0.22 Wm-2.