Climate Thresholds

Present processes of the climate system of the earth lead to a more or less stable equilibrium state of main components like the radiation budget or the global temperature, while the stability is a result of interacting feedback processes. Climate feedback processes differ from each other by resulting in either negative or positive feedbacks. E.g., a negative feedback is described by the Stefan-Boltzmann equation. An initial increase of temperature leads to increased longwave radiation and thus reduces heating again. This describes a negative feedback since the sign of the initial change signal is reversed (warming leads to cooling and vice versa). This effect works like a thermostat for the climate system.

On the other hand there are processes, like the ice-albedo-effect resulting in positive feedbacks. Here a reduction of the surface amount covered with ice leads to an additional warming and further reduction of ice. Vice versa a growing ice shield may lead to further cooling and further growing of the ice surface. Which of the two possible directions of positive feedback mechanisms is active, i.e., whether a warming or a cooling impulse is amplified, is mainly a question of exceeding thresholds in the climate system.

In prinicipal the mixture of and weighting between negative and positive feedback mechanisms is responsible for many phenomena visible in climate system of the past like transitions between the climate modes of glacial and interglacial periods within the Pleistocene. But also at the present many processes may amplify climate change impulses.

Running and modifying a conceptual energy balance model of the earth, the main mechanisms and complexity of interacting feedback mechanisms depending on climate thresholds is explored.