Shipping regulations lead to large reduction in cloud perturbations.

Area of Science:

• Atmospheric Science
• Climate Science
• Oceanography

Background:

• Global shipping is a major source of sulfur dioxide (SO ₂ ) emissions, contributing 13% to global SO ₂ output.
• SO ₂ oxidizes to sulfate aerosol, which exerts a cooling effect on the planet through direct and indirect radiative mechanisms.
• This sulfate aerosol cooling is a significant factor in Earth's radiative balance and a major source of uncertainty in climate change assessments.

Purpose of the Study:

• To develop a global climatology of ship tracks using automated detection methods.
• To investigate the impact of International Maritime Organization 2020 fuel regulations on ship track prevalence.
• To analyze the nonlinear relationship between SO ₂ emission reductions and ship track changes, considering COVID-19 disruptions.

Main Methods:

• Implementation of a machine-learning algorithm for automated ship track detection and cataloging.
• Analysis of over one million identified ship tracks to establish a global climatology.
• Statistical assessment of ship track trends post-2020 regulations, controlling for global commerce disruptions.

Main Results:

• A global catalog of over one million ship tracks was successfully created.
• A significant, yet nonlinear, decline in global ship track prevalence was observed after the 2020 fuel regulations.
• An 80% reduction in SO ₂ emissions resulted in only a 25% decrease in detected ship tracks.

Conclusions:

• Automated detection of ship tracks provides a robust method for global climate impact studies.
• The 2020 maritime fuel regulations have demonstrably reduced ship track formation, but with a nonlinear response.
• Further research is needed to fully understand the complex relationship between emission reductions and climate forcing from shipping.