Snow and ice are among nature's biggest reflectors of sunlight. The shortlist of other materials that reflect so much include white sand, salt flats.
Earth’s climate has slammed in and out of ice ages because of a feedback process that is fundamentally linked to snow’s whiteness or “albedo,” which is an ice reflectivity feedback with air temperature. A cool summer allows snow pack to remain longer, reflecting more sunlight back to space than without the snow. If enough cool summers happen in a row, glaciers coalesce and flood valleys below. The white landscape keeps the air cool. Scientists have worked out “snowball earth” scenarios when the albedo feedback dominates – and therefore cools -- the planet.
But the feedback works in reverse, as well. Warm air melts snow and the heating causes ice crystals to wilt. The fewer jagged edges promote less scattering of light, more heating, more melting and in turn more solar energy absorption. It’s not a runaway feedback loop. Rather, it’s an amplifier of change and is why the Arctic warms or cools at about twice the rate of lower latitudes.