Previous work analyzing clouds in shipping lanes showed that large ships spewing tiny particles into the sky change the characteristics of clouds. More aerosol particles -- tiny natural or manmade bits of dirt, water and gas, such as from pollution -- increase the number of droplets in clouds and make each droplet smaller. This reflects more sunlight from the surface, and the clouds appear brighter.
But the previous work revealed that some parts of the clouds above shipping lanes became brighter and other parts darker, suggesting that using aerosols to increase cloud reflectivity will be more complex than simply adding more.
To better understand that complexity, researchers from Department of Energy's Pacific Northwest National Laboratory performed some exploratory computer simulations to determine the net effect of increased aerosols. They simulated three ships chugging along in a 93-mile by 37-mile block of the Pacific Ocean a few hundred miles southwest of Los Angeles.
Results revealed that introducing additional particles into the model near the surface -- as proposed for geoengineering -- would make the clouds significantly more reflective than they would otherwise be, in certain situations. They found that if the clouds were already drizzling then the new particles would not brighten them very effectively.
Details of the research--such as other cloud, weather and climate characteristics affected by aerosols, like how long the brighter clouds last, whether they burn off when the sun comes up, and what happens when they finally rain--will be discussed in the AAAS presentation. The team is also using the simulations to test when the best time to spray seawater using the simulations is -- in the morning, late afternoon or perhaps all night long.
Although ship tracks are helping researchers explore geoengineering methods, the real plans won't use polluting aerosols from ships. Instead, climate scientists suggest that ocean vessels could spray seawater aerosols into the sky to brighten clouds. But many questions remain about how effective, predictable and safe such methods might be.
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