Dr Nikos Benas and Dr Jan Fokke Meirink of the Royal Netherlands Meteorological Institute and Dr Rob Roebeling of EUMETSAT’s User Support & Climate Services published a case study exploring the impact of maritime shipping pollution on clouds.
When ships emit aerosols – tiny particles of sulfur dioxide and black carbon – via their exhaust, this causes changes in the clouds above which has far-reaching impacts on the global climate, according to the researchers.
Satellite observations
Satellite observations make it possible to study the relationship between shipping pollution and clouds. The researchers set out to see if satellite observations can be used to detect changes in cloud properties as a result of shipping pollution and assessed how new regulations to limit the sulfur content of fuel oil in ships – imposed by the International Maritime Organization (IMO) at the beginning of 2020 – affected cloud properties.
The authors analyzed satellite data from 2004-2023 for a 700km-wide section off the western Atlantic coast of Southern Africa through which a shipping route passes and found that the number of cloud droplets was highest near the shipping track and decreased with distance. They also observed that the size of the droplets was smallest near the shipping track and increased with distance.
“For cloud droplets to form, there need to be particles for water vapor to condense onto and polluted air has a greater number of these particles,” said Roebeling. “Because there is only a certain amount of vapor in a cloud, the water then becomes distributed over more particles. So, in polluted areas, you find clouds containing more but smaller droplets. Our work confirms this known effect. What we want to show people through our case study is that satellite data sets can be used to see this.”
Analyzing the data
By comparing data records for this same area from before and after the IMO 2020 regulation – limiting sulfur emissions from fuel oil in ships – was put into effect, the team was also able to see that the regulation substantially reduced these effects of pollution on clouds.
“It is too early to quantify the effects that changes in low-level clouds may have on Earth’s climate,” said Roebeling. “However, we clearly see that clouds above shipping tracks are different than those above nearby unpolluted areas and that clouds in the region we investigated became more transparent since the new IMO regulations were introduced.”
To find out more about how pollution is affecting how cloud formation, read Meteorological Technology International‘s exclusive feature, “How are microplastics affecting how cloud formation?”, here.
