The Radiator and the Insulator — An Essay on the Thermal Limit of a Civilization

We debate climate change as if it had a single cause, CO₂. This essay argues there is a second, deeper one, almost never stated: the heat we ourselves produce. Negligible today (~1% of greenhouse-gas forcing), it becomes dominant within one to two centuries if consumption keeps growing — whatever the energy source. The essay separates three warming mechanisms — the insulator (CO₂), the radiator (energy destocking), and albedo — and draws from them a single sustainability criterion: only already-absorbed solar flux is thermally neutral, and any destocking is tolerable only if it is CO₂-free and kept below a quantified threshold (on the order of 0.3 W/m²). It derives a sequencing — first put out CO₂ with mature tools, then live on the flux within the Earth's limit, then grow off-world — and proposes the governance instrument such a budget implies: a tradable destocking permit, a cap on added heat (a power, not a stock) as the successor to the carbon quota. The framework converges with Tom Murphy's waste-heat argument (2011), which it extends on three points.