Earth reflects approximately 30% of incoming sunlight back to space.
This reflectivity is known as Earth’s planetary albedo. Clouds, atmospheric particles, snow, ice, deserts, and other bright surfaces reflect sunlight, while oceans, forests, and many darker surfaces absorb more of it. The remaining roughly 70% is absorbed by the atmosphere, land, and oceans.
Albedo is a ratio rather than a fixed physical constant. Earth’s average value changes with cloud cover, seasonal snow and ice, aerosols, and surface conditions. A fresh snowfield has a much higher albedo than open ocean, so replacing reflective ice with dark seawater increases absorbed solar energy.
The 30% figure is an approximate global average and can vary slightly among datasets and time periods. It should not be confused with the greenhouse effect, which concerns how the atmosphere absorbs and re-emits outgoing infrared radiation.