Abstract
Motivated by the extremely important role of the Earth’s vegetation dynamics in climate changes, we study the stochastic variability of a simple climate–vegetation system. In the case of deterministic dynamics, the system has one stable equilibrium and limit cycle or two stable equilibria corresponding to two opposite (cold and warm) climate–vegetation states. These states are divided by a separatrix going across a point of unstable equilibrium. Some possible stochastic scenarios caused by different externally induced natural and anthropogenic processes inherit properties of deterministic behaviour and drastically change the system dynamics. We demonstrate that the system transitions across its separatrix occur with increasing noise intensity. The climate–vegetation system therewith fluctuates, transits and localizes in the vicinity of its attractor. We show that this phenomenon occurs within some critical range of noise intensities. A noise-induced shift into the range of smaller global average temperatures corresponding to substantial oscillations of the Earth’s vegetation cover is revealed. Our analysis demonstrates that the climate–vegetation interactions essentially contribute to climate dynamics and should be taken into account in more precise and complex models of climate variability.
Highlights
Whether or not all physical mechanisms and their correlations were determined or described in detail, the fact that they relate the climate and land surface changes was observed and reported even many years ago
The nonlinear feedback model coupling the Earth’s climate and vegetation is studied in the idealized case of deterministic dynamics. This analysis details the main features of deterministic dynamics and, in particular, it demonstrates the system attractors
Further we show that the evolutionary behaviour of the climate–vegetation system drastically depends on externally induced stochastic forcing which, in turn, can be caused by different anthropogenic and natural processes influencing the nonlinear dynamics
Summary
Whether or not all physical mechanisms and their correlations were determined or described in detail, the fact that they relate the climate and land surface changes was observed and reported even many years ago. The land–atmosphere interactions link the carbon dioxide cycle (CO2 assimilation and diffusion into the leaves and water vapour through transpiration) and water use in plants This mechanism is very sensitive to light intensity, air temperature, precipitation, soil–water content, plant diversity and atmospheric carbon dioxide concentration which would lead to an unstable climate dynamics [7,23,24,25,26]. The vegetation feedback involves in particular the alteration of surface albedo, land roughness and atmospheric composition of greenhouse gases These mechanisms are responsible for the evolutionary behaviour of the very sensitive and complex climate–vegetation system. This paper is devoted to the influence of external stochastic forcing in a simple climate– vegetation model leading to drastically new dynamic phenomena and demonstrating possible abrupt changes in its evolutionary behaviour
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