The authors of The limits to growth interpreted this standard run as demonstrat- ing that given unchanged human behaviour and technology,economic growth in the world economy would come to an end sometime during the twenty-first cen- tury,and human numbers would go into decline.They did not assert that such tury,and human numbers would go into decline.They did not assert that such outcomes were inevitable.The forecast of disaster was conditional on the perpet- - uation of the historical relationships between the variables in the model,which relationships reflect behaviour modes and technology.In fact,a major motivation for the construction of the world model was to be able to use it to investigate what changes to the historical relationships would be needed to avert the collapse in the world economy.The idea is to use runs of the model with different numerical values for the parameters as 'what if?'experiments,just as we did with the much simpler models earlier in this chapter