Global reduction in ship-tracks from sulfur regulations for shipping fuel

Abstract

Ship-tracks are produced by ship-emitted aerosols interacting with low clouds. Here, we apply deep learning models on satellite data to produce the first 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 because of background conditions. Ship-track frequency is more than 10 times higher than a previous survey, and its interannual fluctuations reflect variations in cross-ocean trade, shipping activity, and fuel regulations. Fuel regulation can alter both detected frequency and shipping routes due to cost. The 2020 fuel regulation, together with the coronavirus disease 2019 pandemic, reduced ship-track frequency to its lowest level in recent decades across the globe and may have ushered in an era of low frequency. The regulation reduces the aerosol indirect forcing from ship emissions by 46% or between 0.02 and 0.27 W m −2 given its current estimates.

Changes in CCN activity of ship exhaust particles induced by fuel sulfur content reduction and wet scrubbing

“…39,40 As a consequence, while reducing PM emissions, this can make generally hydrophobic diesel engine exhaust particles more hygroscopic and thus, have an climate cooling effect by increasing direct aerosol radiation scattering as well as indirect cloud-aerosol interactions. A recent survey of global ship-tracks by Yuan et al 41 shows, for example, that the FSC limits implemented in 2015 caused strong reductions in ship-track density in SECAs, due to reduced emissions of sulfur and general shifts in shipping routes. Moreover, the authors find that global 2020 fuel standards led annual mean ship-track density to decrease by 50% or more compared to the climatological mean in major shipping lanes.…”

“…However, FSC regulations appear to have opposing effects on microphysical properties of marine clouds within SECA and non-SECA regions. 41 In this study a marine test-bed engine was used to characterize how international regulations targeting emission reductions of airborne pollutants from the shipping sector, i.e. usage of low FSC fuels and wet scrubbers, alter CCN formation abilities of submicron exhaust particles.…”

“…However, FSC regulations appear to have opposing effects on microphysical properties of marine clouds within SECA and non-SECA regions. 41…”

Strong Anthropogenic Cloud Perturbations Can Persist for Multiple Days

“…Sampling the entire lifespan is challenging for trained human experts, and this might not be an easy task for machine learning methods. Our results can be used to evaluate the quality of the machine learning methods (Watson-Parris et al, 2022;Yuan et al, 2019Yuan et al, , 2022 in sampling the lifespan of polluted cloud tracks. In the future, we plan to use geostationary satellite data to study the temporal evolution of cloud properties downwind of the aerosol point sources (Gryspeerdt et al, 2021;Rahu et al, 2022).…”

“…Machine learning methods are actively developed to detect polluted cloud tracks (Watson-Parris et al, 2022;Yuan et al, 2019Yuan et al, , 2022. Thus far, snapshots from polar orbiters have been used to detect pollution tracks, but geostationary data similarly reveals the pollution tracks.…”