Radiation and Earth's Energy Balance

Radiation and Temperature

Warmer objects radiate at higher frequencies and shorter wavelengths.
A universal relationship between wavelength and frequency applies across all radiating objects.
For any object to radiate, its temperature must be slightly above absolute zero.
Small temperature changes result in large emission changes, following a T^4 exponential relationship.

The sun's energy travels through space without needing a medium.
Visible light constitutes only about 1\% of the total electromagnetic spectrum and readily penetrates the Earth's atmosphere.
The unseen 99\% of the spectrum has powerful effects, with atmospheric gases scattering and absorbing much of it.
Earth absorbs high-frequency, shortwave radiation (e.g., ultraviolet, visible light) and re-emits longwave infrared radiation to cool.

A black body is a theoretical object that emits and absorbs the maximum possible radiation for its given temperature.
Planck's curves illustrate the amount of radiation emitted at different wavelengths for various temperatures.
The sun, with a temperature of approximately 5800 Kelvin, has a peak radiation at around 0.4 micrometers.

In an ideal steady state, incoming energy to Earth should equal outgoing energy.
Earth's energy balance is dynamic and constantly changing due to its rotation and other factors.
The Fundamental Energy Flow Theory posits high-energy solar input and lower-energy terrestrial output.

Albedo is the ratio of reflected radiation to received radiation, indicating a surface's reflectivity.
High albedo surfaces, such as snow, ice, and clouds, reflect 70-90\% of incoming radiation, contributing to cooler temperatures.
Low albedo surfaces, including oceans, forests, and dark soils, absorb 80-95\% of incoming radiation, leading to warmer temperatures.
Alterations in Earth's surface albedo (e.g., deforestation, changes in cloud cover) significantly impact the planet's overall energy balance.

Atmospheric windows are specific wavelength ranges where radiation can pass through the atmosphere unimpeded.
Visible light largely passes through Earth's atmosphere due to a large atmospheric window.
Infrared radiation is heavily absorbed by atmospheric gases; for example, carbon dioxide exhibits strong absorption particularly around the 15 micrometer wavelength.