Albedo is a simple concept that plays complicated roles in climate and astronomy

Dark objects left out in the sun get warm. Lighter-colored objects, not so much. On a planetary scale, this simple, familiar phenomenon—associated with a characteristic called albedo—drives weather and climate. On a regional scale, it can influence the melting of sea ice and glaciers. Open ocean and ice exhibit a big disparity in albedo. Sea ice covered with fresh snow reflects roughly 85% of the sunlight that falls on it, whereas open Arctic waters reflect only about 7%. Image credit: Shutterstock/Maxim Tupikov. And yet, as with many factors influencing climate, albedo’s effects are complicated. Changes in Earth’s overall albedo, for example, influence the planet’s average temperature, which in turn affects the amount of water vapor the atmosphere can hold, which in turn affects our planet’s cloudiness—which in turn affects the planet’s albedo, starting the cycle anew. Because researchers often have difficulty determining how strong such feedbacks are, it’s hard to incorporate them in climate models. But this seemingly simple concept extends beyond scrutiny of Earth to the study of other heavenly bodies. For decades, albedo has helped astronomers assess our planet’s risk of damage from rogue asteroids by offering a means of estimating their sizes. In the future, albedo could even help astronomers identify exoplanets that are possibly hospitable to life, as changes in albedo could indicate changing cloud cover, weather, and large amounts of liquid—possibly even seas—on their surfaces. Understanding darkness and light has a broad spectrum of implications. The word albedo derives from an ancient language (in Latin, albus means white ), but the term’s use in science has a relatively modern origin: It first appeared in a 1760 treatise on optics by Swiss polymath Johann Heinrich Lambert. Since then, the term has become especially useful in astronomy, planetary science, and climatology. In the strictest sense, albedo—or whiteness —is …