For some important resources the almost nent within the next few decades. Estimates not be based on current consumption rate must account for the probable increase of tion of' "dynamic life time", which can be share will accelerate the

exhaustion of stocks is immi- "life time" of resources must a "static" life time index) but rate. This leads to the calcula-shorter than the static life time. Calculation of static and dynamic life time can at best serve to determine the bounds of actual life time of a resource. As a resource becomes scarce, its consump- tion must approach zero thus lengthening the calculated life time. The relative amount of remaining resources, i.e. scarcity, will therefore determine the development of the consumption rate. If material is recycled, it is important to know how quickly a product is scrapped and material is returned to the production process. A model de-scribing the dynamics of nonrenewable resource use must account for these processes.