Radiative Forcing and Surface Temperature Change through Aerosol-Cloud Interactions from the 2020 IMO Global Shipping Emissions Regulations (Invited Presentation)

In 2020 the International Maritime Organization (IMO) instituted new regulations limiting the sulfur content of fuel in ships (IMO2020). Satellite evidence indicates that the IMO2020 regulations have dramatically reduced visible ship tracks, similar to earlier regulations in specific emissions zones near populated coasts. This work synthesizes observations and simulations of the IMO2020 regulations’ impact on clouds and radiative forcing of climate through aerosol-cloud interactions in visible and non-visible ship tracks. There is solid observational evidence that there has been a reduction in ship tracks globally and changes in large-scale cloud properties in certain shipping corridors. Pollution from ships mostly cools the planet through aerosol-cloud interactions. Simulations indicate a small climate effect of warming estimated from the IMO2020 changes and a reduction in ship tracks. Simulations from multiple models have been assessed, but more work is welcome. This warming brings forward expected reductions in aerosol radiative forcing and is expected to have slightly accelerated anthropogenic radiative forcing and climate change since 2020.