Researchers measured for the first time exactly how ship emissions affect clouds at a regional scale, by measuring cloud properties inside the shipping corridor using satellite data and compared them to what they estimated the values would be without shipping activity.
A team lead by the University of Washington atmospheric scientist Michael Diamond and colleagues examined more than a decade of cloud patterns over a busy shipping lane in the southeast Atlantic that connects Europe to southern Africa and Asia.
Accordingly, scientists have theorized that the long, thin cloud patterns referred to as “ship tracks” resulting from the small airborne particles emitted by ships might alter climate by affecting the amount of sunlight reaching the earth’s surface.
The scientists measred the cloud properties in the shipping corridor through satellite data and then compared them to what they estimated the values would be without shipping activity. Then, they fond out that shipping activity rose the number of cloud droplets over the shipping lane that in turn prevented about 2 Watts of solar energy from reaching each square meter of ocean surface along the shipping lane.
Using natural-color images of ship tracks over the southeast Atlantic Ocean as observed on by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite, the scientists compared the average cloud droplet concentrations from 2003 to 2015 during the cloudiest months for the region (September, October, and November) with the expected cloud droplet concentrations without shipping activity.
University of Washington scientist Michael Diamond commented that
If you look at a satellite image of a high-traffic shipping area when the weather conditions are right, you can clearly see bright lines of clouds right along where those ships are traveling and emitting aerosols … Ship tracks are a prime example of how tiny particles of pollution in the atmosphere can influence cloud properties.
He further explained that the aerosols from the ships create “seeds” in the atmosphere that water vapor can latch onto and condense into small cloud droplets. These smaller droplets make clouds brighter so that they reflect more sunlight, which creates a local cooling effect at the planet’s surface.
The co-author Hannah Director of the University of Washington of the study added that “change is small on a regional scale, but it could be enough to affect global temperatures if the same phenomenon occurs worldwide.”
Concluding, the algorithms developed for the study could be also used to study other anthropogenic sources of pollution around the world. “We can use a similar methodology to determine the effects of other human sources of aerosols like power plants.
