Earthshine is the name given to light reflected off of Earth into outer space. The quantification of the the magnitude of the earthshine is referred to as albedo. Major contributing factors in the Earth's albedo are things such as the composition of the atmosphere (such as water vapour content) and whitecaps on the surface of the ocean.
How Can We Observe Earthshine from Earth?
Earthshine is visible with the naked eye when the moon is not full. Gaze into the dark portion of the moon. Do you see the soft glow in the dark area? The illumination of the dark portion of the moon is caused by earthshine.
Recent studies have shown that measurements of earthshine closely track global warming trends, and can tell scientists Earth's energy output into space. For example, one set of research appearing in the Geophysical Research Letters showed that light reflecting off of the oceans whitecaps reflects about 15 million megawatts back into space. That's a significant amount of energy!