As you've learned, some solar radiation is absorbed by Earth and some is reflected. Incoming solar energy consists of shortwave radiation. About 50% of the sun's shortwave energy is absorbed by the surface of our planet. Once the energy is absorbed, it is changed to heat or infrared radiation. When solar energy is re-emitted back from the surface of the earth, it is transmitted as longwave infrared radiation. As you learned on the last page, different types of clouds can block or transmit the sun's incoming shortwave radiation. However, the same clouds that can transmit shortwave radiation cannot transmit longwave radiation. Therefore, when the solar energy absorbed at the surface of the Earth is re-emitted back into space, some of that energy is blocked by clouds and absorbed by the atmosphere.

The radiation absorbed by the atmosphere creates a warming trend in the lower atmosphere, known as the greenhouse effect. Earth's greenhouse effect essentially traps heat and helps regulate our planet's temperature. Without the greenhouse effect, our planet would likely not be habitable for life as we know it!

An enhancement of Earth's natural greenhouse effect is what concerns scientists. Certain gases that make up our atmosphere are better at absorbing radiation and trapping heat. These greenhouse gases include carbon dioxide, methane, water vapor, and nitrogen oxides.

The animation on the next page explains Earth's greenhouse effect.