Implications of Exceeding Sustainable Scale
Ecosystems are generally designed to be sustainable under a broad range of conditions, and can continue providing some level of services even beyond sustainable scale. But if pushed beyond this range by human activities, they react in unpredictable ways. For example, changes are not necessarily linear with respect to the levels of stress applied. A doubling of atmospheric greenhouse gas concentrations beyond preindustrial levels will have more than twice the impact of a 50% increase. At some level of continued disruption, an ecosystem will flip into a different equilibrium state, and may do so quite rapidly. The ecosystem’s natural resilience will assist in maintaining the old equilibrium, but as resilience declines, the likelihood of an equilibrium flip increases. Our knowledge of global ecosystems is totally inadequate to allow us to predict when such flips might occur. Therefore, the longer we exceed sustainable scale, the greater is the risk of reaching and exceeding maximum scale – the point of no return (see Unsustainable Scale).