Environmental (Commonwealth Union)_ In a surprising twist of environmental science, efforts to reduce pollution from global shipping may be playing an unintended role in accelerating global warming. While the primary driver of climate change remains the accumulation of heat-trapping greenhouse gases from burning fossil fuels, scientists are investigating whether a sudden decline in sulphur-rich ship emissions has inadvertently contributed to rising temperatures.
This theory resurfaced in early 2024 when January was declared the hottest on record, continuing an unprecedented streak of global temperature anomalies that began in mid-2023. Could a well-intended maritime policy be fueling the very crisis it seeks to mitigate?
On January 1, 2020, the International Maritime Organization (IMO), a UN agency regulating the global shipping industry, mandated a drastic reduction in the sulphur content of marine fuels, lowering the allowable limit from 3.5% to 0.5%. The aim was clear: to curb harmful sulphur oxide emissions, which contribute to strokes, lung diseases, and cardiovascular conditions.
The regulation was expected to eliminate 8.5 million tons of sulphur oxide emissions annually, and research published in Earth System Science Data confirmed a drop of 7.4 million tons between 2019 and 2020. Compliance has been remarkably high, with only 67 recorded violations since the rule came into effect. While some regions, such as the Baltic Sea and North America, already had stricter limits, this global measure significantly reduced atmospheric sulphur pollution.
Sulphur oxides differ from greenhouse gases like carbon dioxide and methane in that they do not trap heat. Instead, these airborne particles enhance the reflectivity of clouds, making them more mirror-like and better at bouncing incoming solar radiation back into space. This phenomenon, known as the “albedo effect,” has long masked some of the warming caused by greenhouse gases.
With the sudden decline in sulphur pollution, scientists have detected noticeable changes in cloud formations above major shipping lanes. According to Olivier Boucher from the French National Center for Scientific Research (CNRS), these changes include the emergence of larger particles that reflect less sunlight. While this shift may have accelerated recent warming, the precise extent remains difficult to quantify.
Some studies suggest that the IMO regulation could contribute to an annual temperature increase of up to 0.05 degrees Celsius through 2029. A study published in Earth’s Future in August 2023 argued that the significant reduction in airborne sulphur pollution helps explain the extreme heat of 2023. However, the researchers cautioned that multiple factors, including ongoing greenhouse gas emissions and natural climate variability, likely played a role in the year’s record-breaking temperatures.
Although sulphur pollution reductions may have had an unintended short-term warming effect, it is crucial to recognize that sulphur oxides also pose severe health risks and contribute to acid rain. Restoring these emissions is not a viable climate solution. Instead, the focus should remain on reducing carbon dioxide and methane emissions while developing other cooling strategies to counteract warming trends.
As the world navigates the complex interplay of environmental policies and climate effects, this case underscores the need for a holistic approach to mitigating climate change—one that accounts for both the benefits and potential side effects of well-intended interventions.
