Higgins Paul A T, Mastrandrea Michael D, Schneider Stephen H
Department of Biological Sciences, Stanford University, CA 94305, USA.
Philos Trans R Soc Lond B Biol Sci. 2002 May 29;357(1421):647-55. doi: 10.1098/rstb.2001.1043.
Interactions between subunits of the global climate-biosphere system (e.g. atmosphere, ocean, biosphere and cryosphere) often lead to behaviour that is not evident when each subunit is viewed in isolation. This newly evident behaviour is an emergent property of the coupled subsystems. Interactions between thermohaline circulation and climate illustrate one emergent property of coupling ocean and atmospheric circulation. The multiple thermohaline circulation equilibria that result caused abrupt climate changes in the past and may cause abrupt climate changes in the future. Similarly, coupling between the climate system and ecosystem structure and function produces complex behaviour in certain regions. For example, atmosphere-biosphere interactions in the Sahel region of West Africa lead to multiple stable equilibria. Either wet or dry climate equilibria can occur under otherwise identical forcing conditions. The equilibrium reached is dependent on past history (i.e. initial conditions), and relatively small perturbations to either climate or vegetation can cause switching between the two equilibria. Both thermohaline circulation and the climate-vegetation system in the Sahel are prone to abrupt changes that may be irreversible. This complicates the relatively linear view of global changes held in many scientific and policy communities. Emergent properties of coupled socio-natural systems add yet another layer of complexity to the policy debate. As a result, the social and economic consequences of possible global changes are likely to be underestimated in most conventional analyses because these nonlinear, abrupt and irreversible responses are insufficiently considered.
全球气候 - 生物圈系统各子系统（如大气、海洋、生物圈和冰冻圈）之间的相互作用，往往会导致一些在孤立看待每个子系统时并不明显的行为。这种新出现的行为是耦合子系统的一种涌现特性。热盐环流与气候之间的相互作用，就说明了海洋与大气环流耦合的一种涌现特性。由此产生的多个热盐环流平衡，在过去曾导致气候突变，在未来也可能引发气候突变。同样，气候系统与生态系统结构和功能之间的耦合，在某些地区会产生复杂的行为。例如，西非萨赫勒地区的大气 - 生物圈相互作用会导致多种稳定平衡。在其他条件相同的强迫条件下，可能出现湿润或干燥的气候平衡。所达到的平衡取决于过去的历史（即初始条件），对气候或植被的相对较小扰动都可能导致两种平衡之间的转换。萨赫勒地区的热盐环流和气候 - 植被系统都容易发生可能不可逆的突变。这使得许多科学和政策界持有的相对线性的全球变化观点变得复杂。耦合的社会 - 自然系统的涌现特性给政策辩论增添了另一层复杂性。因此，在大多数传统分析中，可能的全球变化的社会和经济后果很可能被低估，因为这些非线性、突变和不可逆的反应没有得到充分考虑。
