Paradoxical! How reducing ship pollution is increasing global warming (with the “Cessation Shock”)

An 80% reduction in sulfur dioxide emissions observed in early 2020 could be associated with substantial atmospheric warming in some ocean regions, a new study suggests. Researchers say that “we are changing the clouds,” and an inadvertent geoengineering test is fueling record heat in the oceans.

In 2020, regulations imposed by the United Nations’ International Maritime Organization (IMO) reduced sulfur pollution from ships by over 80%, leading to significant improvements in global air quality. However, these same regulations might have had an unintended consequence: the lower sulfur content in ship fuel could be linked to an increase in ocean warming.

Recent research suggests that the reduction in maritime pollution in 2020 caused a substantial “disruption shock,” which may have doubled the long-term average rate of global warming.

Before 2020, global shipping relied on “dirty,” high-sulfur fuels that produced significant air pollution. Interestingly, these polluting particles blocked sunlight, contributing to cloud formation and helping to slow ocean warming.

Oceans clouds

@Communications Earth & Environment

With the new regulations that drastically cut sulfur content in fuels starting in early 2020, the subsequent drop in polluting particles has significantly increased the amount of heat trapped at Earth’s surface, exacerbating the climate crisis. Researchers have likened this sudden end to decades of maritime pollution to an unintentional geoengineering experiment, revealing new insights into its effectiveness and associated risks.

Oceans Clouds 2

@Communications Earth & Environment

Ocean surface temperatures hit record highs in 2023, alarming experts who struggled to explain the massive increases. Scientists behind the new study suggest that reduced sulfur pollution might be a “fairly substantial” factor. Others believe it is only a minor contributor and that the reasons for the extraordinary rise in sea and planetary temperatures remain a concerning mystery.

Expert insights

Tianle Yuan of the University of Maryland, who led the study, noted that the estimate of an additional 0.2 watts per square meter of heat trapped in the oceans after the pollution reduction is “a big number, and it happened in one year, so it’s a big shock to the system.”

As a result, since 1880, we are likely to experience a warming rate roughly twice the long-term average, he said. The warming effect of reduced pollution is expected to last about seven years.

Analyzing the impact

The research combined satellite observations of sulfur pollution and computer models to calculate the impact of the reduction. It found that the short-term shock was equivalent to 80% of the total additional warming the planet has seen since 2020, due to long-term factors like rising fossil fuel emissions.

Scientists used relatively simple climate models to estimate how much this might increase the average global surface temperature, finding an increase of about 0.29°F (0.16°C) over seven years.

However, other scientists believe that the impact on temperature from pollution reduction will be significantly lower due to various feedback mechanisms within the climate system, which are included in more sophisticated climate models. The results of this more comprehensive analysis are expected by the end of 2024.

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