The Greenhouse Effect

Atmosphere acts like a blanket, keeping the surface warm.

Think about this. Where do we get the biggest night/day temperature swings on the Earth? Few clouds or water molecules in the atmosphere - radiational cooling is efficient.

Venus has a thick carbon dioxide atmosphere -- very effective at absorbing (and trapping) infrared radiation.

The Greenhouse effect:

Steps in the Greenhouse process

Sunlight (visible) penetrates Venus' cloud layers, hits surface
Surface heats up
Surface emits infrared energy (heat)
Infrared trapped; doesn't get out.
Surface continues heating

Eventually a new thermal equilibrium is reached, with the upper atmosphere radiating energy at the correct rate to counterbalance the energy coming in from the Sun. But the temperature in the lower atmosphere is much, much hotter.

This occurs on Earth, too, which is why the Earth isn't at -1 F. But it is done largely by water (H₂0) clouds. If we continue to put CO₂ and other so-called greenhouse gases into the Earth's atmosphere, Earth will start to warm significantly (may already be happening!). Even a few degree rise in temperature can have a dramatic impact on the Earth (melting polar caps, flooding, drought, famine...)