CO2 and the Greenhouse Effect
Sunlight passes through the atmosphere and warms Earth’s surface. As the heat is radiated from Earth’s surface into space, greenhouse gases (GHGs), such as water vapor, carbon dioxide, and other gases, trap some of the heat, slowing its departure and sending some heat back to the surface. Molecules of GHG are continuously absorbing and releasing heat, indirectly warming the surrounding atmosphere and Earth’s surface as the heat remains on the planet longer.
Currently, the natural greenhouse effect is maintaining an average annual temperature of about 59°F (15°C) at the surface of Earth. Without the greenhouse effect, the average annual temperature at Earth’s surface would be around 0°F (−18°C)!1
The intensity of the greenhouse effect remains steady as long as the conditions remain about the same. Changes in the amounts and types of GHGs in the atmosphere, conditions at Earth’s surface, and the amount of energy reaching Earth from the Sun could increase or decrease the greenhouse effect, rendering Earth warmer or colder, respectively, than today.
www.physicalgeography.net/fundamentals/7h.html (accessed July 16, 2015).