Cleaning ship emissions may accelerate global warming more than previously thought

A sharp drop in sulphur dioxide emissions from ships since 2020 could mean the planet will warm more than expected this decade, but researchers are divided on the magnitude of the temperature change.

“If our calculations are correct, this decade will be a really warm one.” Tienle Yuan Combined with background warming from rising greenhouse gas concentrations, 2023's record-breaking temperatures could become “the norm” for years to come, said Yuan of the University of Maryland, Baltimore County, a change he described as an unintended “geoengineering termination shock.”

But other climate researchers say they have problems with the new figures. “This is a timely study, but it makes some very bold statements about temperature change and geoengineering that are difficult to justify on the basis of evidence,” they said. Laura Wilcox At the University of Reading, UK.

The study adds another chapter to the ongoing debate among climate scientists about the impact of International Maritime Organization (IMO) rules to drastically reduce sulfur dioxide pollution emissions from ships after 2020. Increased air pollution from the burning of heavy marine fuels is Linked Tens of thousands of people die every year.

But these aerosols also had a cooling effect on the climate by directly reflecting solar radiation and brightening clouds over the oceans. Be expected Deep cuts in these emissions would result in some warming due to the loss of the cooling effect of sulfur dioxide, but the amount of warming projected varies widely.

Yuan and his colleagues are now using satellite observations of cloud conditions and mathematical models that show how clouds will change in response to the expected reduction in sulfur aerosols to estimate the warming effect of the 2020 regulations.

The researchers calculated that this reduction in precipitation increased the amount of solar energy warming the ocean by 0.1 to 0.3 watts per square meter, about double previous estimates. The effect was more severe in areas with high shipping activity. The North Atlantic, which has been unusually hot since last year, saw warming effects more than three times higher than normal, the study said.

The researchers then used a simplified climate model that excluded the effects of the deep ocean to calculate how this warming effect (called “radiative forcing”) would change global temperatures. They found that the 2020 change would increase the global average temperature by an additional 0.16°C over the seven years after emissions were reduced, effectively doubling the rate of warming over this period compared to previous decades.

“This forcing is not greenhouse gas forcing. It's shocking,” Yuan said, “so it will be a blip in the temperature record over the last decade.”

The new figures are high, but Quote If you use other methods, Michael Diamond A research team from Florida State University measured changes in cloud cover in a region of the Atlantic Ocean since 2020 and found that the modeling results matched.

But other researchers have disputed how the team calculated global temperature changes. Zeke Hausfather Researchers at the climate think tank Berkeley Earth say the researchers conflated the effects of warming on the oceans with global warming, and that simplified climate models showed a faster rise in temperatures than in reality. “With modern climate models, it's very hard to justify warming of more than 0.1°C in the near future,” Hausfather says.

But if the new estimates are accurate, they could help explain some of the temperature spikes seen over the past year. Rising concentrations of greenhouse gases from fossil fuel burning and a shift toward the El Niño weather pattern are responsible for much of the heat, but unexplained gaps have sparked debate about whether climate change is accelerating.

“[The change in shipping emissions] “It goes some way to filling in the gaps that we've identified.” Gavin Schmidt At NASA. But that's not all.