Does depolluting ship fuel accelerate global warming ?

This publication comes as the planet has been setting heat records since June 2023, particularly at the surface of the oceans, which reached an absolute high in March 2024 (21.07°C). piotr borkowski/Getty Images

Does the depollution of ship fuel accelerate global warming ? At the heart of a scientific controversy for a year, this question found a new echo this Thursday, May 30, 2024, with the publication of # 39;s study highlighting the role of this new regulation on the record temperatures of 2023.

This regulation from the International Maritime Organization (IMO), which has significantly lowered the sulfur content of ships' fuel oil since January 1, 2020, has "contributed to the abnormal warming that we experienced in 2023 and 2024", declared to AFP Tianle Yuan, researcher at the University of Maryland and lead author of this American study, published in the journal Communications Earth & Environment.

This is "a significant warming effect" which "will practically double the rate of warming for the 2020s", underlined Mr. Yuan, in pointing "a particularly strong impact on the North Atlantic", an ocean marked in 2023 by unprecedented marine heatwaves.< /p>

This phenomenon would find its source in the cooling effect of sulfur dioxides, emitted during the combustion of heavy fuel oil by ships. These aerosols help reflect and absorb the sun's rays and promote the formation of clouds, which absorb less heat than the oceans. The sulfur emitted by ships thus mitigates global warming, itself due to the accumulation of greenhouse gases emitted by human activities.

Introduced to improve air quality, the IMO regulations have been particularly effective, reducing sulfur emissions from maritime transport by 80% since 2020, underlines the study, which estimates that it could, however, cause a rise in global temperature of 0.16°C over seven years.

This publication comes as the planet has been setting heat records since June 2023, particularly at the surface of the oceans, which reached an absolute high in March 2024 (21.07°C).

"Terminal shock"

The authors of the study compare IMO regulations to "terminal shock" and "involuntary" from a geoengineering experiment. This science of climate manipulation, which aims to counter the effects of global warming, studies the injection of large-scale aerosols into the atmosphere or lightening marine clouds so that they better reflect the sun's rays.

The authors also believe that their results suggest that'Marine cloud brightening may be a viable geoengineering method to temporarily cool the atmosphere'.

"We have been waiting for a long time for warming associated with improvement in air quality. We called it the "climate penalty" (climate penalty, editor's note) air quality policies", noted Nicolas Bellouin, professor of climatology at the University of Reading (United Kingdom ).

"The maritime industry had even bet on this, without success, to avoid having to use cleaner, and therefore more expensive, fuels&quot ;, recalled the researcher who did not participate in this study, that he judges "more scientifically solid than the previous studies".

"But I think the contribution" of the drop in ship emissions &amp ;quot;the anomaly of (temperature of) 2023 and future warming rates remains an open question", he adds, pointing out certain limits of the study.

The question has been agitating the scientific community for almost a year. Until now, most climate scientists believed that reducing emissions from the maritime sector could only explain a small part of the rise in temperatures, on the order of a few hundredths of a degree. , according to an oft-cited article published by Carbon Brief.

"There is little debate that aerosols cool the climate, but there is much uncertainty about whether aerosols cool the climate. magnitude of this cooling effect", underlined Edward Gryspeerdt, researcher at Imperial College London, cited by the British Science Media Centre.

"History has shown us that natural variabilities have been overinterpreted in the past", a added to AFP Jean-Louis Dufresne, climatologist, research director at CNRS, who estimates "complicated" d'analyze "small disturbances over short periods of time".