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Dynamics of climate and ecosystem coupling: abrupt changes and multiple equilibria.
Paul A T Higgins1, Michael D Mastrandrea, Stephen H Schneider
1Department of Biological Sciences, Stanford University, CA 94305, USA. phiggins@stanford.edu
Summary
Global climate and biosphere systems exhibit emergent behaviors, like abrupt climate shifts, due to subsystem interactions. These complex, nonlinear responses are often underestimated in policy and economic analyses.
Area of Science:
- Earth System Science
- Climate Science
- Ecology
Background:
- Global climate and biosphere subsystems (atmosphere, ocean, biosphere, cryosphere) interact, producing emergent behaviors not seen in isolation.
- Emergent properties arise from coupled subsystems, such as interactions between thermohaline circulation and climate, leading to multiple equilibria.
- Past abrupt climate changes and potential future shifts are linked to these emergent properties, complicating linear global change views.
Purpose of the Study:
- To highlight emergent properties in coupled climate-biosphere systems.
- To explain how these properties can lead to abrupt and potentially irreversible changes.
- To underscore the underestimation of nonlinear global changes in scientific and policy discussions.
Main Methods:
- Analysis of interactions between global climate and biosphere subsystems.
- Examination of emergent properties in coupled systems, using thermohaline circulation and Sahel climate-vegetation dynamics as examples.
- Review of historical data and modeling of system equilibria and transitions.
Main Results:
- Coupled ocean-atmosphere circulation exhibits emergent properties, like multiple thermohaline circulation equilibria, causing past and potential future abrupt climate changes.
- Atmosphere-biosphere interactions in the Sahel create multiple stable climate-vegetation equilibria (wet or dry), dependent on initial conditions.
- Small perturbations can trigger switches between equilibria, demonstrating the potential for abrupt, irreversible shifts in coupled socio-natural systems.
Conclusions:
- Emergent properties of coupled climate-biosphere systems lead to nonlinear, abrupt, and potentially irreversible changes.
- These complex dynamics, including multiple equilibria and history dependence, challenge linear models of global change.
- Conventional analyses likely underestimate the social and economic consequences of global changes due to insufficient consideration of these emergent properties.
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