- In what was described at the time as “the biggest change in the history of the oil market”, the International Maritime Organization (IMO) pushed through new standards on 1 January 2020 to reduce the sulfur content of fuel to 0.5% from 3.5%.
- The rule change led to an 80% reduction in sulfur dioxide emissions, a team of scientists reported in a recent paper, and may help explain why last year’s record heat was so extreme.
- Tianle Yuan, a scientist at the University of Maryland and lead author of the study, said via social media that the impact of the Clean Air Regulation could be described as an “unintentional geoengineering event.”
Countries at the UN International Maritime Organization meeting in London signed an agreement to reach net zero emissions from shipping by “or thereabouts” by 2050.
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A sweeping regulatory change in 2020 to reduce air pollution from the world’s ships may have played a role in increasing global average temperatures, a controversial study has found.
In what was described at the time as “the biggest change in the history of the oil market”, the International Maritime Organization (IMO) pushed through new standards on 1 January 2020 to reduce the sulfur content of fuel to 0.5% from 3.5%.
The rule change led to an 80% reduction in sulfur dioxide emissions, a team of scientists reported in a paper published May 30 in the journal Communications Earth & Environment, and may help explain why last year’s record heat was so extreme.
Tianle Yuan, a scientist at the University of Maryland and lead author of the study, said via social media that the impact of the Clean Air Regulation could be described as an “unintentional geoengineering event.”
That’s because sulfur dioxide, a pollutant produced when sulfur-containing fuel like coal or petroleum oil is burned, reacts with water vapor to form aerosols that reflect sunlight back into space.
Aerosols have a direct cooling effect, although climate scientists note that their contribution to global cooling or warming when reduced remains a complex area of research.
Describing this as accidental geoengineering and citing numbers that may overestimate the impacts could lead to false assumptions about policies designed to limit future emissions.
Laura Wilcox
Associate Professor at the National Center for Atmospheric Science at the University of Reading
The study said the sudden drop in sulfur emissions from 2020 supports the viability of marine cloud brightening, an area of growing scientific interest that some researchers say could be used to cool the planet.
The question of whether reductions in sulfur dioxide emissions may have contributed to global warming is not new to climatologists, but the debate has recently resurfaced following extreme heat waves in the North Atlantic and many areas of Europe.
Extreme temperatures are fueled by the climate crisis, the main driver of which is the burning of fossil fuels.
“There are three interesting things that people are trying to figure out why 2023 was so alarmingly warm, and the first one that everyone has heard about is El Nino,” Jim Haywood, a professor of atmospheric science at the University of Exeter in the United Kingdom, told CNBC. via telephone.
“The second thing that people are not quite aware of is Hunga Tonga, which was an explosive volcanic eruption that was very unusual… And the third is the IMO shipping regulations,” Haywood said.
The El Nino weather phenomenon, a naturally occurring climate pattern that helped fuel a spike in global temperatures, has recently shown signs of ending, according to the United Nations Meteorological Agency. A return to the cooling effect of La Nina weather is expected later this year.
Aerial top view of container ship at full speed with beautiful wave pattern for logistics, import export, shipping or shipping.
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“You have such stellar climate scientists [former NASA scientist] Jim Hansen made the argument that we’re not going to get a rebound and the heat trace isn’t going to go back down into the pack — and I think I’m kind of with him on that one,” Haywood said.
“I think there are so many ways that aerosol-cloud interactions can be underestimated in climate models that it could have had an accelerating impact,” he added.
“It’s very hard to quantify exactly how much. All the climate models will give you slightly different answers because of the way they do their sulfur dioxide emissions,” Haywood said. “So we’re not sure how much of an impact the IMO regulations will have on average global temperatures.”
Scientists not involved in the paper generally welcomed the study as timely, but some said the research could exaggerate the impact of IMO regulations.
Joel Hirschi, deputy head of marine systems modeling at the UK’s National Oceanographic Centre, said the study showed that reducing the sulfur content of marine fuel from 2020 was likely to accelerate the warming of the planet.
However, Hirschi said the authors likely overestimated the impact of reducing sulfur in marine fuel on the record global temperatures seen last year and in 2024.
“The record high temperatures we saw in 2023 and 2024 are remarkable and cannot be explained by a single factor. Research continues into why recent temperatures were so high and reduced sulfur in marine fuel is just one contributing factor.” Hirschi said.
Separately, Laura Wilcox, an associate professor at the National Center for Atmospheric Science at the University of Reading in the UK, said the study “makes very bold claims about temperature change and geoengineering that seem difficult to justify on the evidence”.
“For many people, switching to lower-sulfur marine fuel, which causes less air pollution and reduces aerosol emissions, is a shift away from human impacts on the climate, as well as a step that reduces the health effects of air pollution,” Wilcox said.
“Describing it as random geoengineering and citing numbers that may overestimate the impacts could lead to false assumptions about policies designed to limit future emissions,” she added.