The greenhouse effect involves the thermal radiation from the Earth’s surface being absorbed and re-emitted by gases in the atmosphere, termed greenhouse gases. The re-emitted radiation, much of which is in the infrared region of the spectrum, is sent out in all directions, meaning that some of the energy is sent back down toward the lower atmosphere and the Earth’s surface. This results in an overall increase in the surface temperature due to the presence of the greenhouse gases. It should be noted that a certain amount of this greenhouse effect is entirely natural, but the effect can be increased when additional greenhouse gases are introduced into the atmosphere as a result of human activity.

As a side note, the name for this effect arises from the fact that greenhouses allow solar radiation to pass through glass and remain inside. In fact, a greenhouse operates on a different principle; the presence of the glass walls in a greenhouse prevent heat from being lost due to convection currents.