Shaving Cream Prank or Ship Tracks?


I could have sworn I saw this same foamy pattern the other day while cleaning my oven, but no, this is NASA’s latest image of ship tracks over the northeast Pacific Ocean near the coast of Oregon and Washington. The microscopic particles, or aerosols, in ship engine exhaust make good seeds for water condensation under the right atmospheric conditions, creating the clouds in their wake. Years ago it was debatable whether these anthropogenic clouds were helping to cool the Earth or warm it. Last I heard the verdict was that the clouds trap more heat in the lower atmosphere, thereby warming things up.

But the NASA Earth Observatory folks report a new twist to this:

The aerosol particles may be natural—such as desert dust or sea salt—or artificial, including the particles emitted by ships. The particles in ship exhaust are more abundant than natural airborne particles such as sea salt, so they generate more and smaller cloud droplets. Because of this, ship tracks tend to be brighter than other clouds. Water droplets are essentially tiny spheres, and a smaller sphere has a greater surface-to-volume ratio than a bigger sphere. In other words, a littler droplet has a greater surface area, relative to its volume, than a bigger droplet. The greater surface area means more sunlight reflected back into space.

Winter Wonderland Photos

That means ships can have two completely opposite effects on climate. One one hand they are releasing tons of climate warming carbon dioxide by burning fossil fuels. On the other hand, they are helping to reflect more sunlight back into space, which keeps some solar energy from being captured by the oceans and atmosphere.

This visible light image was captured on January 15 by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Aqua satellite, and provided courtesy of Jeff Schmaltz of LANCE MODIS Rapid Response.

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