Without greenhouse gases, Earth's temperature would be:

• A. Too cold at night and too hot during the day
• B. Too hot at night and too cold during the day
• C. Unchanged
• D. Much warmer overall

Answer: (A)

Greenhouse gases act like a blanket around Earth, trapping some of the heat the surface emits and keeping temperatures from swinging too wildly. If that blanket were removed, heat would escape to space more easily at night, so nighttime temperatures would plunge—nights would be too cold. During the day, sunlight would still heat the surface, but without the insulating blanket to moderate the heat, daytime temperatures could rise more than usual in many places, making days feel too hot. So the idea that nights become very cold while days become very hot captures the expected effect of losing that greenhouse blanket.