The impacts of human actions on ecosystems are often slow to become apparent. Also, some changes are difficult to predict, because they are gradual only until they reach a certain threshold, at which large changes occur suddenly.
Examples of abrupt changes include the start of epidemics, the collapse of a fish population, and shifts of lakes from a clear to a turbid state. On a larger scale, regional climate systems and also social systems may change abruptly if a tipping point is reached.
Recent scientific advances have demonstrated that in the vicinity of such tipping points complex systems such as societies, ecosystems and climate systems may gradually lose resilience. They become increasingly fragile, to the point that small perturbations may trigger an irreversible shift to another state. Scientists across a range of disciplines have now turned their focus for sustainability studies on resilience, defined as the ability of a system to maintain its essential functions in the face of perturbations.
The reason for this is that while perturbations such as earthquakes or droughts cannot be controlled or managed, resilience usually can. The challenge thus is to find out what determines the resilience of different complex systems. This is a scientific field in development, in which interaction of disciplines is obviously required.
Better case studies, experiments, theories and models are needed to understand the links between ecosystem change and impacts on human well-being and to assess the economic consequences of ecosystem change.
