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Article Dans Une Revue Bulletin of the American Meteorological Society Année : 2016

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

Résumé

The response of the various climatic processes to climate change can amplify (positive feedback) or damp (negative feedback) the initial temperature perturbation. An example of a positive feedback is the surface albedo feedback: when the surface temperature rises, part of the ice and snow melts leading to an increase in the solar radiation absorbed by the surface and to an enhanced surface warming. Positive feedbacks can lead to instability. On Venus for example, a positive feedback is thought to have evolved into a runway greenhouse effect. However, positive feedbacks can exist in stable systems. This paper presents a simple representation of a positive feedback in both a stable and an unstable system. A simple experimental device based on a scale principle is introduced to illustrate the positive feedback and its stabilization or runaway regimes. Stabilization can be achieved whether the amplitude of the positive feedback declines (e.g. "saturation" of the feedback) or remains constant. The device can also be used to illustrate the existence of tipping points, which are threshold values beyond which the amplification due to feedbacks or the stability of the system suddenly changes. The physical equations of the device are established in the framework of the feedback analysis. Key features to understand why a positive feedback does not necessarily lead to a runaway effect are described. The analogy between the different components of the device and those of the climate system is established. Finally, the contribution of individual feedbacks to the total climate response is addressed. (Capsule Summary)To illustrate the concepts of positive feedback, stability, instability, tipping point and saturated feedback we conceive a very simple device based on a scale with two water reservoirs.
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Dates et versions

hal-01384430 , version 1 (26-10-2016)

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Jean-Louis Dufresne, Marion Saint-Lu. Positive feedback in climate: stabilization or runaway, illustrated by a simple experiment. Bulletin of the American Meteorological Society, 2016, 97 (5), pp.755-765. ⟨10.1175/BAMS-D-14-00022.1⟩. ⟨hal-01384430⟩
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