The pervasiveness of scale problems adds to both the difficulties in understanding sustainable scale issues, and the dangers they pose. It is difficult enough to understand a single complex system operating in a relatively stable natural state. The complexities are increased significantly when multiple complex systems are affected simultaneously, and are interacting in novel and dynamic ways. If we have already driven one or more global systems beyond sustainable scale, as many scientists believe, then the risks of a domino effect triggering yet more systems' changes is increased. Considerable caution is required to ensure all global life support systems are maintained in a sustainable range (see Scale Policy Implications).