Ice and Climate Feedbacks
Part of the Climate Change exhibition.
Part of the Climate Change exhibition.
Why are the roofs of so many yellow school buses painted white? Why do skiers wear silvered goggles? It's all because light surfaces reflect solar radiation more than dark surfaces. The scientific term for how much a surface reflects sunlight is albedo (al-BEE-doh).
The surface of the deep ocean is very good at absorbing heat; it soaks up solar radiation almost as effectively as the asphalt on a city street. The most reflective natural surface is fresh, dry snow. That difference—between the reflectivity of snow and absorbency of the ocean—is a key dynamic in Earth's climate system.
In climate science, feedbacks are responses that either increase or diminish the effects of processes that change climate. For instance, when ice and snow melt because the air is warming, that melting reduces the surface that reflects the Sun's rays—and this in turn increases the ongoing warming. Feedbacks are crucial elements of the climate system—and they make predicting climate change more difficult.
Dark soil exposed in early spring illustrates the scientific principle of feedback on a small scale. As the reflective snow melts, the dark, energy-absorbent earth is exposed, which speeds the melting.
When it comes to albedo, snow and ice vary more than you might think. Here's how much of the energy that falls on these surfaces bounces back into space.
Snow-covered forest: 25 percent
Sea ice with no snow: 30 percent
Old, melting snow: 50 percent
Old, dry snow: 70 percent
Fresh, dry snow: 80 percent
Physical interactive 5.7
Of all the energy reaching Earth from the Sun, about two-thirds is absorbed by land, ocean and atmosphere, and one-third is reflected back into space. Most of the absorbing takes place in the tropics, where dark, plant-covered land and dark ocean predominate. Much of the reflecting happens at the poles, with their bright coverings of snow and ice.