World models are still in the early phases of development, and the majority of the ones built so far do not deal with the resources and environment sectors adequately. Of the models available, only the Leontief input-output model considers these two sectors in some detail. Even then the results should be taken as ordersof-magnitude guesses rather than as figures that can be used in an operational sense. Furthermore, the Leontief model suffers from a basic defect: it is a pollution abatement model. From the resources and environmental standpoint, it would be much more preferable to consider this as a sector within an overall management framework in which pollution control could play an important part.
Modelling of world problematique is still in an early stage of development, and much work remains to be done to improve its basic structures, underlying assumptions, and data availability. Because of the difficulties—both conceptual and practical—many important areas are not considered in the resources and environment fields, or, if considered, are dealt with only superficially. An example is the consideration of the extent of recycling, conservation, and materials substitution, as prices of individual resources increase—owing either to economic market forces or man-made factors. While the general direction of the main thrusts are known, it is still difficult to define limits and determine interlinkages with any high degree of confidence. Much further work will be necessary to establish these interrelationships, the components of which will also need to have an adequate data-base.