Nonlinear Dynamics of the Climate System

Abstract

The problem of climate change requires to attribute observed climate variations to natural sources of variability and anthropogenic forcing factors. Climate variability from the decadal over centennial to the millennial time scales and the transitions from glacials to interglacials are determined by strong nonlinear interactions between the changes in the incoming solar radiation, its absorption in the atmosphere and the ocean and the initiation of large ice sheets which has a strong influence on the quasi-stationary atmospheric waves. The climate we experience results from both ordered and nonlinear chaotic behaviour. It is very hard to determine the nonlinear chaotic component and to know how important it is. The equations to define atmospheric and climate system behavior are nonlinear. This characteristic of the equations allows the system to be highly sensitive to small differences in the initial states and to result in very different large-scale responses to small changes. This tendency promotes transitions between a number of quasi-stationary atmospheric circulation states that can influence regional circulation systems and its variability as well as the climate as a whole. Because of the possibility that different paleoindicators could be more sensitive to variations in one regime than in the others, the interpretation of paleoclimatic data should be revisited in the light of the circulation regime concept. The evolution of the climate system on long time scales is determined by the large-scale nonlinear dynamics of the interacting climate subsystems and external forcing factors. The nonlinear feedbacks via momentum, heat and moisture fluxes between relatively fast changes in preferred atmospheric circulation regimes and the slowly evolving subsystems ocean, sea-ice and ice-sheets are the processes responsible for the initiation of glacials or interglacials and the complex reorganization of the whole climate system. Various mechanisms have been invoked to explain sudden regional and climate changes and transitions, including variations of the North Atlantic thermohaline circulation as trigger or amplifier in rapid climate changes, carbon dioxide and methane concentrations, surface albedo of ice, snow and vegetation, water vapor feedbacks and dust and particles feedbacks. The importance of these feedbacks in sudden changes depends on the atmospheric and oceanic circulation patterns, determined by internal circulation modes and the nonlinear coupling of the climate subsystems.