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Artificial clouds made by humans may become so common they change the Earth's climate. The long thin cloud streaks that dominate the above satellite photograph of Georgia are contrails, cirrus clouds created by airplanes. The exhaust of an airplane engine can create a contrail by saturating the surrounding air with extra moisture. The wings of a plane can similarly create contrails by dropping the temperature and causing small ice-crystals to form. Contrails have become more than an oddity - they may be significantly increasing the cloudiness of Earth, reflecting sunlight back into space by day, and heat radiation back to Earth even at night. The effect on climate is a topic of much research.
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