Impacts of shipping fuel regulations on global warming

The 2020 International Maritime Organization regulation (IMO2020) limits sulfur in shipping fuel to improve health and air quality. This change reduced sulfate aerosol emissions, which in turn weakened the cooling effect normally provided by marine clouds.

A recent study by Zhang et al. used machine learning to distinguish natural climate variability from human-driven changes and found that the regulation contributed to additional greenhouse gas warming. However, the climate signal from this effect remains difficult to detect because of strong natural fluctuations in cloud properties, except in the southeastern Atlantic where it is more pronounced.

These results suggest that cutting aerosol emissions in the future could speed up warming, and that deliberate interventions like marine cloud brightening would need to be very strong to stand out against natural climate fluctuations.