Positive feedback in climate stabilization or runaway, illustrated by a simple experiment

Jean-Louis Dufresne and Marion Saint-Lu conceive a very simple device based on a scale principle with two water reservoirs to demonstrate the concepts of positive feedback, stability, instability, tipping point, and saturated feedback. The atmospheric water vapor amount increases with temperature following the Clausius-Clapeyron law assuming fixed relative humidity. As water vapor is a powerful greenhouse gas, such an increase contributes to a further warming of the climate. This positive feedback loop amplifies a given perturbation of the surface temperature by about a factor of 2. This feedback is amplified as the climate warms owing to the increase in the tropopause height.