Unless special action is taken, human resource use and emissions will continue to increase as a consequence of growth in population in human activity. Importantly, this "human footprint" - if unchecked - will grow beyond the carrying capacity of the globe, that is beyond what the globe can provide on a sustainable basis. If such expansion into unsustainable territory is allowed to happen, decline - or collapse - in human resource use and emissions become unavoidable.
The limits of growth was a milestone in which the Club of Rome for the first time used complex mathematical models for predictions on future interdependencies of social, environmental and economic factors. The models took into account the limited availabilitiy of natural ressources, the output of the global industry, food production, population growth and the pollution of the environment.
Meadows, D., Randers, J., Meadows, D. and Behrens, W. (1974) The Limits to growth: A report for the Club of Rome's Project on the Predicament of Mankind, Universe Books; 2nd edition