“Reduced Sulfur Emissions from Shipping Industry Contributed to Record Warmth in 2023, Study Finds”

Last year, 2023, was recorded as Earth’s warmest year on record. A new study led by scientists at the Department of Energy’s Pacific Northwest National Laboratory has found that nearly 20 percent of this record warmth can be attributed to reduced sulfur emissions from the shipping industry. The study, published in the journal Geophysical Research Letters, highlights the impact of regulations put into effect by the International Maritime Organization in 2020, which required an 80 percent reduction in the sulfur content of shipping fuel used globally.

When ships burn fuel, sulfur dioxide is released into the atmosphere. This sulfur dioxide can lead to the formation of sulfur aerosols, which can have a cooling effect on Earth’s surface by reflecting sunlight. The reduction in sulfur emissions meant fewer sulfur aerosols were being released into the atmosphere, leading to a decrease in the formation of these cooling clouds known as ship tracks.

Using a machine learning approach to analyze over a million satellite images, the researchers estimated a 25 to 50 percent reduction in visible ship tracks. Where the cloud count was down, the degree of warming was generally up. Climate models used in the study showed that roughly half of the potential warming from the changes in shipping emissions had already materialized in just four years, with more warming expected in the future.

While changes in sulfur emissions played a significant role in the record warmth of 2023, the authors note that other factors such as greenhouse gas concentrations also contribute to global temperature change. Aerosols, like sulfur emissions, can mask some of the warming effects of greenhouse gases, but they are shorter-lived and can lead to sudden spikes in warming when their concentrations decrease.

Lead author Andrew Gettelman emphasized the importance of understanding the climate response to changes in emissions as the world moves towards decarbonization. The study also highlights the uncertainties surrounding aerosols and their impact on climate projections, calling for better data and modeling to improve our understanding.

In addition to Gettelman, Earth scientist Matthew Christensen, also a PNNL author, contributed to the study, which was funded in part by the National Oceanic and Atmospheric Administration. The research underscores the complex interplay between emissions, aerosols, and climate change, emphasizing the need for continued research in this area.