Major Cuts in Shipping Pollution Actually Made Climate Change Worse, Scientists Find

No good deed goes unpunished.

Heat Check

In 2020, the International Maritime Organization passed a global standard to drastically cut down on the use of high-sulfur fuels in the shipping industry. It did what it set out to do almost immediately, with NASA scientists finding noticeably less pollution along shipping lanes that same year.

But now, new research suggests that the environmental measure may have had the unintended effect of worsening climate change — at least in the short run.

As detailed in a study, published in the journal Communications Earth & Environment and spotlighted by The Guardian, those airborne particles, or aerosols, were actually helping to block heat from the Sun. Once they were steeply curtailed, however, more solar radiation was able to stay trapped in our atmosphere — a phenomenon that could help explain why 2023 was the hottest year on record by a huge margin.

The findings illustrate the unpredictable complexities of both modeling and combating climate change, while also serving as a preview of the risks of solar geoengineering efforts to cool our sweltering planet.

Global Warm-up

The researchers used satellite observations and a chemical transport model to calculate radiative forcing, or the change in energy in the Earth's atmosphere, after the curtailing of sulfur emissions.

They confirmed that the measure reduced human aerosols in the atmosphere along shipping routes. In turn, that caused an average uptick of about 0.2 watts per square meter of radiative forcing — though this strongly varied from region to region.

For reference, a global doubling of CO2 levels would cause about 4 watts per square meter of radiative forcing — so it's a "big number," study co-author Tianle Yuan at the University of Maryland told The Guardian, especially since "it happened in one year."

"We will experience about double the warming rate compared to the long-term average [since 1880]," Yuan added.

However, some scientists have since pointed out that there are simply too many uncertainties involved to definitively say how much of the heating is attributable to the sulfur drop-off.

"The [pollution cut] is certainly a contributing factor to the recent warmth, but it only goes a small way toward explaining the 0.3C, 0.4C, and 0.5C margins of monthly records set in the second half of 2023," Zeke Hausfather, a climate scientist from the University of California, Berkley who was not involved in the study, told The Guardian.

Second Thoughts

At any rate, the work should give pause to advocates of solar geoengineering techniques, such as marine cloud brightening, which involves pumping aerosols into the atmosphere to block sunlight.

Even if these techniques worked, scientists fear that we'd have to keep them up forever. Otherwise, there could be a "termination shock" — the moment we stop releasing aerosols, global temperatures would sharply climb again, and then we'd find ourselves in the same, if not worse, pickle.

The abrupt curtailing of sulfur emissions from the shipping industry, the researchers say, inadvertently served as an experiment illustrating this effect. Still, take this as just one piece of the puzzle. It doesn't necessarily mean we should discount these radical methods completely — and it definitely doesn't mean that we should give up on curtailing pollution, either.

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