The Disappearance of Ship Tracks – On the Impact of Sulfur Reduction in Marine Fuel on the Climate

Abstract

In response to concerns regarding human health and environmental protection, the International Maritime Organization (IMO) adopted the IMO 2020 regulation, which reduced the sulfur content in marine fuel from 3.5% to 0.5%. This regulation, effective since 2020, has significantly reduced sulfur dioxide (SO2) emissions from ships by more than 80%. However, this reduction has led to the unintended consequence of diminishing the atmospheric cooling effects provided by sulfate aerosols, which previously contributed to the formation of clouds known as ship tracks, cloud brightening, and the scattering of solar radiation. This loss has potentially exacerbated global warming. This thesis investigates the climatic impact of the IMO 2020 regulation through a comparative literature review, analyzing divergent views within the scientific community. Key discrepancies are highlighted between the Intergovernmental Panel on Climate Change (IPCC) and climate scientist James E. Hansen and his colleagues. The IPCC's 6th Assessment Report downplays the cooling effect of pre-2020 shipping emissions, whereas other studies indicate a significant cooling influence for the same period. In particular, recent publications co-authored by Hansen demonstrate that the IMO 2020 regulation has considerably reduced the formation of ship tracks and contributed to recent warming. There is now compelling evidence that the IMO 2020 regulation has led to an increase in absorbed solar radiation, resulting in an acceleration of global warming rates. This indicates that sulfur reductions are contributing to the occurrence of more extreme weather events. The thesis concludes that while sulfur reductions are intended to improve human health and reduce premature deaths attributable to ship emissions, the climatic repercussions necessitate reevaluation. The findings call for an improved understanding of aerosol impacts to enhance climate models and propose deliberate geoengineering measures, such as marine cloud brightening via aerosol injection, to mitigate the unintended warming effects of sulfur emission reductions.