International shipping sulfur dioxide emissions 1970-2022

Global sulfur dioxide (SO2) emissions from international shipping totaled 3.7 million metric tons in 2022. This represented overall emission reductions of almost 75 percent when compared to 2008, the year in which shipping SO2 emissions peaked at just over 14 million metric tons.

Why have shipping SO2 emissions fallen? 

The shipping industry is responsible for releasing large volumes of toxic air pollutants into the atmosphere each year. In a bid to address this issue, the International Maritime Organization (IMO) introduced new regulations in 2019 that lowered the maximum percentage of sulfur content in marine fuels from 3.5 percent to 0.5 percent. As a result, SO2 emissions from shipping plummeted 70 percent the following year, to just three million metric tons. 

Impacts of falling SO2 emissions 

In addition to being a major pollutant, SO2 also provides a cooling effect on the climate by reflecting some incoming solar radiation back into space. As such, it is believed that a reduction in SO2 can result in additional global warming. This has led some scientists to link the recent spike in global average sea surface temperature to the new IMO regulations. However, it is not yet clear how big a contribution these reductions have made, with several other factors likely contributing to the fast-rising temperature.