Ship Tracks - Findings

Findings

It is theorised that sulfur dioxide released from ships' smokestacks could be forming sulfate aerosol particles in the atmosphere, which cause the clouds to be more reflective, carry more water and possibly stop precipitating. This is regarded as proof that humans have been creating and modifying clouds for generations through the combustion of fossil fuels.

Although ship tracks can sometimes be visible, researchers usually scan the near-infrared light coming off the clouds. At this wavelength many ship tracks appear as bright lines that can be distinguished from the surrounding, uncontaminated clouds. On average, polluted clouds reflect more sunlight than their unaffected counterparts.

When compared to normal clouds, the number of water droplets per volume of air in ship tracks are more than doubled, the radius of the drops is decreased by roughly six percent and the total volume of liquid water per volume of air is increased twofold. In other words, this excessive cloud seeding from the ship causes the clouds to retain more water. Normally, rain forms when cloud drops coagulate and reach a size where gravity can pull them to the ground. Yet, in ship tracks, the cloud seeding made the drops so small that they could no longer easily merge to reach the size needed to escape. Since no drizzle comes out of the seeded clouds, the liquid water just keeps building in the cloud. This makes the cloud brighter and more reflective to incoming sunlight, especially in the near-infrared part of the spectrum.