List several types of surfaces and their albedo values. Explain the differences among these surfaces. What determines the reflectivity of a surface?

The reflectivity of surfaces, commonly known in physical geography as albedo, plays a key role in determining the Earth's climate and energy balance. Essentially, albedo quantifies how much light that hits a surface is reflected without being absorbed. Think of it like a mirror: a surface with higher reflectivity will act similar to a brighter mirror, bouncing most of the light away, while a lower reflectivity surface is like a darker mirror, absorbing more light. The concept of albedo is not only crucial for understanding global warming and climate change but also for practical applications like designing buildings or even clothing.

When explaining the reflectivity of surfaces to students or readers, it's helpful to use everyday examples. A snowy field glittering under the sun has high reflectivity: it sends most of the sunlight back into the atmosphere. Conversely, a dark asphalt road on a hot day has low reflectivity, retaining more heat. This simple observation leads to a deeper understanding of how different surfaces can drastically influence local temperatures, weather patterns, and even ecosystems.

Surface albedo values provide a numerical way to express the reflectivity of different Earth materials. These values are represented as a fraction or percentage, indicating the portion of incoming energy reflected by a particular surface. To paint a clearer picture for students, let's consider a range of typical albedo values:

• Snow: 80-90% or 0.8-0.9, meaning most sunlight is reflected.
• Sand: Approx. 40%, indicating a significant, but lower, reflectivity.
• Forest: Roughly 10-20%, demonstrating moderate absorption and reflection.
• Water: Varies greatly, from about 10% to as high as 80%, depending on factors such as the angle of incoming light.
• Asphalt: 5-20% or 0.05-0.2, absorbing most of the sunlight, converting it to heat.

Recognizing these values is fundamental when studying the Earth’s surface, as it helps predict how different environments react to solar radiation, informing strategies for mitigation of urban heat islands or optimizing the placement of solar panels.

The factors determining a surface's reflectivity are just as varied and intricate as albedo values themselves. Principal among these factors is color. Light-colored surfaces, such as glaciers and deserts, have high albedo, meaning they reflect a lot of sunlight and are cooler. Dark-colored surfaces, like forests and oceans, absorb more sunlight and are generally warmer.

Another determinant is texture. Smooth surfaces, like calm bodies of water, reflect sunlight in a consistent direction, which is why we can sometimes see sharp reflections on a lake's surface. Rough or irregular surfaces, such as rocky terrain, scatter reflected light in many directions which can reduce overall reflectivity. Lastly, the angle of incoming light, which changes with latitude, time of day, and season, significantly affects albedo. A surface will reflect differently if the sun is low on the horizon versus directly overhead. By understanding these determinants, students can better grasp why different regions of Earth have varying climates and how human activities, such as urban construction, can change local albedos and consequently, local weather patterns.