Cleaner shipping fuel has accelerated global warming, says study
In 2020, the International Maritime Organization (IMO) implemented a global standard to reduce high-sulfur fuels in shipping, leading to a significant drop in pollution. However, recent research suggests this measure may have unintentionally worsened climate change. The study found that aerosols from high-sulfur fuels were blocking heat from the Sun, and their reduction led to more solar radiation being trapped in our atmosphere. This could explain why 2023 was the hottest year on record by a significant margin.
Study reveals impact of reduced sulfur emissions
The researchers utilized satellite observations and a chemical transport model, to calculate the change in energy in the Earth's atmosphere after sulfur emissions were reduced. They verified that the measure decreased the presence of human aerosols in the atmosphere along shipping routes. However, it led to an average increase of roughly 0.2 watts per square meter of radiative forcing, with variations across regions. Study co-author Tianle Yuan described this as a "big number," especially since "it happened in one year."
Debate over sulfur emissions' role in global warming
While the study's findings are significant, some scientists argue that uncertainties exist. Zeke Hausfather, a climate scientist not involved in the study, stated that while "the [pollution cut] is certainly a contributing factor to the recent warmth," it only partially explains 2023's record temperatures. The IMO rules led to an 80% decline in sulfur dioxide emissions, which form aerosols that reflect sun rays back into space and mask global warming.
Fuel standards' impact on global heat uptake
The researchers estimated that the IMO fuel standards could be responsible for 80% of the planet's total net heat uptake since 2020. The impact was particularly pronounced in busy shipping lanes. Stuart Haszeldine, director of the Edinburgh Climate Change Institute, stated that while exact predictions about global temperatures are challenging to make, the trend is "very clear, extremely worrying and very significant."
Caution against solar geoengineering techniques
The study also warns against solar geoengineering techniques like marine cloud brightening, which comprises pumping aerosols into the atmosphere to block sunlight. Scientists fear that if these techniques were stopped, there could be a "termination shock" where global temperatures would sharply climb again. The abrupt lowering of sulfur emissions from the shipping industry inadvertently served as an experiment illustrating this potential effect.
