Levels of Sustainable Scale  There are many levels of sustainable throughput. Available evidence indicates that up until at least the Industrial Revolution the level of throughput in the global economy was sustainable.  Certainly the level of hunter-gathers’ throughput was sustainable, and considerably lower than the level of throughput in the 16^th century, which was also sustainable. No global ecosystems were challenged by the level of economic throughput until the 19^th or 20^th century. Some levels of throughput provide very little in terms of material goods and services, and some provide considerably more.  Two conceptual levels of sustainable throughput are of particular interest:

• Maximum Sustainable Scale is the highest level of material throughput that remains sustainable; that is, where the rate of throughput is theoretically identical to the rate of regeneration.  Any increase in throughput becomes unsustainable. Maximum sustainable scale is determinded by the biophysical limits of the ecosystems affected by the throughput in question. This conceptual notion of maximum sustainable scale is difficult to quantify precisely, but is nonetheless an important conceptual tool in understanding the dynamics of sustainable scale.

• Optimal Scale is a level of material throughput within the sustainable range ( i.e. where throughput is less than regeneration), which provides the most benefits relative to costs, where the notions of benefits and costs includes ethical and social as well as economic values. Optimal scale is therefore determined by socio-political limits, in addition to biophysical limits of ecosystems.