Earth's Energy Budget and Albedo

Picture 100 units of sunlight hitting the planet. About 30 go straight back to space, bounced off clouds, ice, and bright surfaces — that fraction is the planet's albedo. The other 70 get absorbed, mostly by the surface, since the atmosphere is nearly transparent to visible light. That absorbed energy doesn't just vanish: it warms the surface, which then re-emits it as infrared radiation. Greenhouse gases in the atmosphere are built to catch that infrared, so the atmosphere warms from below, not from sunlight passing through it on the way down. Over time the planet radiates infrared back to space until incoming and outgoing energy roughly balance — that balance point sets Earth's average temperature.

Albedo is why color matters so much for climate. Fresh snow and sea ice reflect 60 to 90 percent of sunlight; they stay cold partly because they refuse to absorb the energy that would warm them. Open ocean water reflects only about 6 percent, swallowing the rest. So when ice melts and exposes dark water or soil, the surface flips from a mirror to a sponge, absorbing far more energy at the same sunlight intensity. More absorbed energy means more warming, which melts more ice, which lowers albedo further — a feedback loop that accelerates itself.

This connects directly to the warming seas and shrinking ice sheets covered elsewhere in global change: albedo loss is one of the clearest amplifiers of warming already set in motion by greenhouse gases, turning a regional melt into a planet-wide energy imbalance.