Tuesday, January 10, 2012
The energy that warms Earth’s atmosphere comes from the Sun, but sunlight does not warm the atmosphere directly. The atmosphere warms from below. Most of the short wavelength, electromagnetic energy from the Sun passes through the atmosphere and is absorbed by the Earth. Absorbing this energy warms the Earth. As the Earth warms, energy re-radiates back into the atmosphere as heat. Eventually, this energy re-radiates from the atmosphere back out into space.
The Earth does not absorb all of the electromagnetic energy that hits it. Some reflects back out into space. This is important for the Earth’s energy balance because only absorbed energy contributes to the temperature of the Earth/atmosphere system. The amount of energy reflected by an object is its Albedo.