The Greenhouse Effect

The Earth receives energy from the Sun in the form of radiation. Much of that radiation doesn't get past our atmosphere, but that which does is responsible for heating up the Earth. As the Earth warms up, it in turn emits Infrared radiation (IR) back into space. Now if it simply sent it all back, we'd be in trouble (and a lot colder). But actually what happens is that "greenhouse gases" in our atmosphere absorb the thermal radiation emitted by the Earth's surface and send the energy back to the Earth's surface, warming it to the relatively comfortable temperatures that we have now. Without this recycling of energy by greenhouse gases (otherwise known as the "Greenhouse Effect") in the atmosphere, the Earth would be about 30 degrees (C) cooler than it is now.

The Greenhouse Effect is an undisputed phenomenon, and there are many naturally occurring greenhouse gases such as water vapor (H2O), carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone. Certain human activities, however, add to the levels of most of these naturally occurring gases, and this is why the Greenhouse Effect is at the center of the climate change debate. The observed increase in the Earth's temperature, associated with global warming, is believed to have been caused by the relatively recent increase in greenhouse gas concentrations from human activity.

A schematic representation of the exchanges of energy between outer space, the Earth's atmosphere, and the Earth surface. The ability of the atmosphere to capture and recycle energy emitted by the Earth surface is the defining characteristic of the greenhouse effect.
© Robert A. Rohde, Global Warming Art Project