Albedo, which is Latin for “whiteness,” measures how much solar radiation a surface reflects. This measurement is fundamental to understanding Earth’s energy balance and how different surfaces interact with sunlight. The relationship between reflectivity and temperature is often misunderstood, leading to confusion about whether a highly reflective surface heats or cools its environment.
What Albedo Measures
Albedo is quantified on a scale ranging from 0 to 1, or 0% to 100%. An albedo of 0 represents perfect absorption, while an albedo of 1 achieves perfect reflection. Most natural and artificial surfaces fall between these two extremes.
Albedo measures the fraction of incoming solar radiation, which includes visible light and infrared radiation, that is returned to space or the atmosphere. For example, a surface with an albedo of 0.3 reflects 30% of the sunlight, absorbing the remaining 70%. This absorbed fraction dictates how much energy is available to be converted into heat.
How Reflected Energy Affects Temperature
A high albedo promotes cooling by preventing solar energy from being absorbed. When solar radiation strikes a highly reflective surface, the energy is scattered back into the atmosphere and into space. This reflected energy bypasses the surface entirely, making it unavailable to generate thermal energy.
Warming occurs only when solar radiation is absorbed by a surface. Absorbed electromagnetic energy is transformed into thermal energy. This conversion causes the molecules of the absorbing material to vibrate faster, resulting in a temperature rise. A low-albedo surface absorbs a greater percentage of this energy, leading to a higher temperature increase.
The fate of the incoming energy—reflection versus absorption—is the defining factor for temperature change. A high-albedo surface reflects most energy, leaving little to be converted into heat. Conversely, a low-albedo surface absorbs the majority, causing a significant temperature spike.
Comparing Common Surfaces
Different materials possess widely varying albedo values, which explains the temperature differences experienced on a hot day. Fresh snow, a high-albedo surface, registers a value between 0.8 and 0.9, reflecting up to 90% of sunlight. This high reflectivity keeps snow-covered regions cool, as solar energy never converts into heat.
In contrast, urban materials like asphalt pavement and black roofing often have values below 0.1, absorbing over 90% of incoming solar energy. This extreme absorption causes these surfaces to become significantly hotter than the surrounding air, contributing to the “urban heat island” effect.
Urban planning utilizes this principle by promoting light-colored concrete and “cool roofs” with higher albedo. These materials reflect more sunlight, lowering surface temperatures and reducing the need for air conditioning.
Albedo’s Role in Planetary Climate
Albedo is instrumental in regulating the planet’s overall temperature through its influence on major surface features. High-albedo surfaces like glaciers and polar ice sheets function as natural mirrors, reflecting a substantial portion of the sun’s energy back into space. This reflective capacity acts as a natural cooling mechanism for the globe.
The ice-albedo feedback loop begins when global temperatures rise, causing ice and snow to melt and expose darker land or ocean water beneath. Since ocean water and bare ground have a lower albedo, they absorb far more solar radiation than the ice they replaced. This increased energy absorption causes further warming, which accelerates more ice melt, creating a self-reinforcing cycle.