The Bathtub Metaphor

A framing for the atmospheric CO₂ accumulation problem. The atmosphere is a bathtub. Emissions are the faucet. Natural absorption by oceans and biosphere is the drain. Stopping new emissions closes the faucet but does not drain the bathtub. Removing legacy carbon is the only way to lower the water level. The metaphor distinguishes between flux (annual emissions) and stock (cumulative atmospheric concentration).