Does the reduction in sulfur oxide emissions from the maritime sector contribute to accelerating climate change? The new heat record set in January surprised scientists, some of whom suggest that the introduction of a new standard in maritime transport in 2020 could be an explanation.
What is the new standard?
Since January 1, 2020, cruise ships, container ships, bulk carriers, and oil tankers sailing the oceans must use fuel with a sulfur content that does not exceed 0.5%, compared to 3.5% previously.
Even stricter restrictions had already existed in certain areas known as « Emission Control Areas (ECA) » in the Baltic Sea, the North Sea, the North American zone, and the Caribbean maritime zone of the United States.
This rule was adopted by the International Maritime Organization (IMO), a UN agency responsible for maritime issues and regulating the sector.
Sulfur aerosols are responsible for many health problems, such as strokes, lung diseases, and cardiovascular diseases.
What has this new rule changed?
Sulfur oxide (SOx) emissions decreased by 7.4 million metric tons in 2020 compared to 2019, according to an article in the Earth System Science Data journal published last June.
This is very close to the IMO’s target of 8.5 million metric tons of SOx, representing a 77% reduction in maritime sector emissions.
According to the organization, in 2023, only two ships were found to have sulfur content above 0.5% in their fuel. Since the new regulation came into force, only 67 violations have been recorded.
Why could this have favored global warming?
Sulfur oxide emissions are categorized as aerosols. These are not greenhouse gases that contribute to global warming. On the contrary, sulfur aerosols help create reflective clouds that send some of the sun’s heat back into space.
Therefore, the reduction in emissions may have played a role in the rise of heat records in recent months, « but we are not able to quantify it with ultra-precise measurements, » says Olivier Boucher, research director at CNRS.
« Several articles show that there is a detectable change in the optical properties of clouds above maritime corridors, » the researcher adds.
In summary, clouds above seas and oceans have changed since 2020; they are made up of larger droplets and are less reflective.
The reduction in sulfur oxide emissions from maritime transport « contributes a little » to global warming, « but we cannot say that it contributes a lot, » says Mr. Boucher.
According to a scientific article published last August in Earth’s Future, the IMO’s standard is expected to lead to a global surface temperature increase of about 0.05°C by 2029.
This drastic reduction in sulfur oxide emissions « helps explain the exceptional heatwaves of 2023, but other parameters must also be taken into account, » the study concludes.
