English: Visible ship tracks in the Nothern Pacific, on March 4th 2009. On an overcast day, the clouds look uniform. However, NASA MODIS images' sesor reveals long skinny trails of brighter clouds hidden within. As ships travel across the ocean, pollution in the ships' exhaust create more cloud drops that are smaller in size, resulting in even brighter clouds. On clear days, ships can actually create new clouds. Water vapor condenses around the particles of pollution, forming streamers of clouds as the ships travel on. The ship tracks themselves are too small to impact global temperatures, but they help us understand how larger pollution sources such as industrial sites or agricultural burning might be changing clouds on a larger scale.