CO2 and other greenhouse gases absorb the infrared (longwave) radiation that is re-emitted by the Earth's surface after it absorbs solar radiation. The Sun's energy arrives as visible and ultraviolet radiation (short wave). Earth's surface absorbs it and re-emits it as infrared radiation. CO2 traps this infrared radiation in the atmosphere, preventing it from escaping to space, thereby warming the planet — this is the greenhouse effect.