Condensation trails (contrails, for short) form as hot, relatively moisture-rich air from jet exhaust cools and decompresses rapidly amidst surrounding, much colder and low-pressure air at high altitudes. Moisture in the exhaust plume condenses and forms ice crystals that linger for varying abounts of time, depending on humidity and winds in the surrounding air. Drier air will evaporate the cloud material sooner; and strong, horizontally shearing or turbulent winds will deform or mix away the contrail faster than weak winds or fairly smooth and uniform flow. Being clouds, they reflect solar radiation (insolation) spaceward, with dense contrail concentrations noticeably reducing the amount of insolation reaching the ground. Here, several layers of cloud texturized the scene, the lowest being fractus, lit orange in the setting sun's rays, then pale-orange tufts of cirrus, then the contrails -- highest and whitest, catching the rays least filtered by intervening atmosphere.
Sugarloaf Key FL (4 Jan 9) Looking WSW