Question

Imagine that the composition of Earth's atmosphere were altered so that its ability to absorb visible and far infrared light were reversed. a. If you were outdoors when the Sun was at its highest point in the sky, how would the sky appear? b. Would there be an increase or a decrease in Earth's average surface temperature?

Short answer

a. The sky would appear black like outer space. b. There would be a decrease in Earth's average surface temperature.

Step-by-step solution

Understanding Light Absorption

The present Earth's atmosphere absorbs some of the incoming solar radiation, including visible light, while allowing infrared radiation to pass through. In the given scenario, the atmosphere's properties would be reversed, absorbing more infrared light and allowing all visible light to pass through.

Analyzing Sky Appearance

Because the atmosphere would no longer absorb or scatter any visible light, all the sunlight would directly reach Earth. Therefore, there would be no Rayleigh scattering, which is responsible for the blue sky, making the sky appear black like outer space.

Impact on Surface Temperature

Currently, the atmosphere absorbs and traps some of the infrared radiation emitted from Earth's surface, contributing to the greenhouse effect. If the atmosphere were absorbing visible light instead, more infrared radiation would escape into space, thus resulting in a decrease in Earth's average surface temperature.

Key concepts

Understanding Light Absorption

Light absorption refers to the process where certain wavelengths of light are taken in (absorbed) by a medium, such as Earth's atmosphere, and not transmitted. Normally, Earth's atmosphere absorbs specific wavelengths from both visible light and infrared radiation. This unique property allows our atmosphere to play a critical role in maintaining climate and weather patterns on Earth.

• In the current atmosphere, some visible light is absorbed.
• Infrared radiation, which is pivotal for heat transfer, has some wavelengths absorbed and some allowed to pass through.

Understanding how light is absorbed helps to comprehend the significance of the atmosphere's role in temperature regulation. If the atmosphere absorbed all visible light, less light would reach the surface, potentially causing a cooling effect. This would alter life's balance on Earth significantly.

The Nature of Visible Light

Visible light encompasses the range of wavelengths that the human eye can detect, from approximately 380 to 750 nanometers. This part of the spectrum is responsible for the diverse array of colors we see every day.

• Visible light is primarily emitted by the Sun.
• It includes all the colors perceived as a rainbow when dispersed.

In a normal scenario, part of this light is absorbed and scattered by the atmosphere, leading to phenomena like the blue sky. If Earth's atmosphere altered to allow all visible light to pass through without absorption or scattering, as in the exercise scenario, the sky would appear black even during the day, resembling outer space. This ability to view direct sunlight would change how we perceive day and nighttime.

Exploring Infrared Radiation

Infrared radiation is a type of electromagnetic radiation with wavelengths longer than visible light, typically ranging from about 700 nanometers to 1 millimeter. Known primarily for its heat-carrying properties, it plays a significant role in the greenhouse effect and the Earth’s energy balance.

• Infrared carries the warmth we feel from sunshine.
• It is crucial for maintaining warmth by trapping heat emitted from Earth's surface.

If the absorption of infrared radiation by Earth's atmosphere was more efficient than that of visible light, it would affect Earth's temperature regulation. Observing a scenario where more infrared escapes due to lesser absorption could lead to a cooler Earth, illustrating the delicate balance managed by our atmospheric composition.

Understanding Rayleigh Scattering

Rayleigh scattering is the scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light. It is responsible for the blue color of the sky because shorter wavelengths (blue and violet) scatter more effectively than other colors.

• This scattering causes the sky to appear blue during the day.
• It depends heavily on the composition and size of atmospheric particles.

If the atmosphere were changed to absorb rather than scatter visible light, Rayleigh scattering would be substantially reduced or eliminated, making the sky appear black even when the Sun is visible. This illustrates the significant role Rayleigh scattering has in how we perceive our environment, emphasizing the effect atmospherical composition has on everyday phenomena.