Michael Diamond, a cloud physicist at Florida State University, has found that the international regulation IMO 2020, which reduced sulfur emissions from ships, has unintentionally darkened marine clouds.
This outcome, observed just three years after the regulation took effect, means less sunlight is reflected back into space, contributing to increased global warming.
IMO 2020 aimed to reduce sulfur in shipping fuels from 3.5% to 0.5% to improve air quality and public health. The regulation has indeed lowered sulfur dioxide and ammonia levels near ports, but it has also led to increased warming.
The reduction in sulfur emissions, which had previously contributed to cooling by creating reflective aerosols, has caused marine clouds to darken, allowing more sunlight to reach Earth’s surface.
The debate over the exact warming effect of IMO 2020 is ongoing. NASA’s Tianle Yuan suggests that the reduction in aerosols could lead to an additional 0.25°C rise in global temperatures this decade, potentially doubling the usual rate of warming. In contrast, Robert Allen from UC Riverside estimates a much smaller impact, suggesting less than 0.05°C increase over 20 years. Differences in their models contribute to this disparity: Yuan uses an energy balance model, while Allen employs an Earth system model with more realistic climate representations.