In today’s global economy, we rely heavily on large cargo ships that traverse the oceans to transport goods. These large vessels burn sulfur-containing fuel. In doing so, they dump sulfur dioxide into the air, which is a known cause of acid rain and respiratory distress in humans. As such, in 2020 the International Maritime Organization (IMO) Marine Environment Protection Committee (MEPC) limited sulfur in marine fuels from the previously accepted 3.5% by mass to 0.5%. This change was made in an attempt to improve air quality worldwide, but researchers have now discovered an unintended consequence: fewer ship track clouds and warmer oceans.
Ship tracks are low lying, reflective clouds that follow in the wake of ships. They form when sulfate particles are released into the atmosphere, seeding and brightening the clouds. Given the sheer number of cargo ships that travel the oceans, a substantial portion of the globe tends to be covered by ship tracks, reflecting the sun’s heat back out to space. In reducing sulfate particles, the IMO regulations have also decreased the prevalence of ship tracks: in two independent studies, Michael Diamond, Tianle Yuan, and colleagues studied these clouds and found that cloud brightness over the oceans has decreased significantly since the regulatory changes in 2020. The prevalence of ship tracks has decreased over 50% in the main shipping corridors after 2020, exposing more of the oceans’ surface to the warming effects of the sun.
This unintentional experiment in geoengineering has shown us not only the wide-reaching impacts of our actions, but also a potential avenue of planet cooling. One way to reflect the sun and keep the oceans cool without polluting the environment is marine cloud brightening, or shooting sea water as tiny droplets up into the air. Most of the water evaporates, leaving behind crystals of salt which can seed clouds, similar to sulfur dioxide. This could be one tool to combat climate change.
These studies were led by Michael Diamond, an assistant professor at Florida State University in the Department of Earth, Ocean and Atmospheric Science, and Tianle Yuan, an assistant research scientist at the University of Maryland, Baltimore County in the Joint Center for Earth Systems Technology.
Managing Correspondent: Stacey Yu
Press Article: “We’re changing the clouds.” An unintended test of geoengineering is fueling record ocean warmth. News from Science
Original Journal Articles: Detection of large-scale cloud microphysical changes within a major shipping corridor after implementation of the International Maritime Organization 2020 fuel sulfur regulations. Atmospheric Chemistry and Physics
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