Energy balance model with ice-albedo feedback: as ice melts, Earth absorbs more solar energy, further warming. Shows bistability, hysteresis, and catastrophic tipping between glacial and warm states.
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Budyko-Sellers EBM: C dT/dt = (1−α(T))S/4 − σ(T−Γ)⁴ + ΔF_CO₂. Ice albedo: α(T) jumps from 0.6 (frozen, T<263K) to 0.3 (ice-free, T>293K), linear between. This nonlinearity creates the bistable S-curve with fold bifurcations at the tipping points.