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Thermal equilibrium in the Sun-Earth system
Intermediate
Earth's temperature is set by radiative balance.
Earth's temperature is set when absorbed solar power equals emitted infrared: S(1 − A)πR² = 4πR²σT⁴, giving T ≈ 255 K without an atmosphere.
Albedo A ≈ 0.3.
Atmosphere adds about 33 K.
In more detail
Earth's temperature is set by a balance between incoming solar energy and outgoing infrared radiation. The Sun's energy input and Earth's albedo and emissivity determine the equilibrium temperature.
Real-world uses
- Climate scientists use energy balance models to predict changes in Earth's temperature.
- Planetary scientists estimate surface temperatures of other worlds using energy balance.
- Climate scientists use radiative balance to estimate how the Earth's temperature responds to changes in the energy it absorbs from the Sun.
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Frequently asked questions
Why does albedo matter?
A brighter surface reflects more sunlight and stays cooler.
Is Earth in perfect balance?
On average, close to balance over long periods, though small imbalances cause warming or cooling trends.
What is radiative balance?
The balance between the energy the Earth receives from the Sun and the energy it radiates back into space.
Related topics in Heat & Thermodynamics
Arrow of time · Humidity and dew point · Greenhouse effect · Thermal conductivity of materials · Insulation and R-value · Heat transfer in everyday life