Shortwave sunlight passes through the atmosphere and warms the surface; the surface re-radiates longwave infrared, some of which is absorbed and re-emitted by greenhouse gas molecules, trapping heat.
ΔF = 5.35 · ln(CO2 / CO2_ref) [W/m²]
σT⁴ = (1-α)·S/4 + ΔF
- CO₂ concentration — greenhouse gas density in the atmosphere shell; more molecules absorb more outgoing IR photons.
- Solar irradiance — incoming shortwave sunlight (yellow photons) striking the planet.
- Cloud/albedo cover — fraction of incoming sunlight reflected back to space before reaching the surface.
- Photon emission rate — how fast the warmed surface emits outgoing infrared (red) photons.
Watch red IR photons bounce between greenhouse gas molecules (glowing dots in the shell) before escaping — more CO₂ means more bounces and a higher equilibrium surface temperature.