Earth's surface temperature is set by a balance between sunlight absorbed and infrared heat radiated back to space. Greenhouse gases like CO2 don't block incoming sunlight, but they do absorb outgoing infrared radiation and re-emit part of it downward, forcing the surface to warm until balance is restored. This model uses the standard logarithmic CO2 forcing relation and a linear climate-sensitivity response, then feeds the resulting temperature into an ice-albedo feedback loop: warmer surface → less polar ice → darker planet → more sunlight absorbed → further warming.
ΔF = 5.35 · ln(CO2 / CO2_ref) (W/m², CO2_ref = 280 ppm)
ΔT = λ · ΔF (λ ≈ 0.8 K per W/m²)
T = T0 + ΔT + feedback(ice loss)
- CO2 concentration — higher CO2 increases the radiative forcing ΔF logarithmically; each doubling of CO2 adds a fixed increment of forcing (~3.7 W/m² per doubling).
- Solar output — the total energy arriving from the sun; small changes shift the baseline temperature directly through the absorbed-flux term, independent of the greenhouse effect.
- Ice-albedo feedback — when enabled, rising temperature shrinks the reflective polar ice caps, lowering planetary albedo and absorbing more sunlight, which amplifies the initial warming.
- Reset to pre-industrial — returns CO2 to 280 ppm and solar output to the modern average (1361 W/m²), the reference state used to compute forcing.
Real-world relevance: this simplified zero-dimensional energy-balance model captures the same core physics used in the first climate projections from the 1970s–80s — full modern climate models add oceans, clouds, aerosols and circulation on top of exactly this radiative balance.