We theoretically explore the interrelations between population (P), affluence (A) and technology (T) for various environmental impacts (I ) using IPAT-type modelling. To illustrate the differences across environmental dimensions, climate and land use impacts are modelled. We use middle-of-the-road projections for population and per capita income and different forecasting methods for technology, including extrapolations of historical trends, models based on stochastic IPAT (STIRPAT) and predictions in the literature. The different approaches are compared within the IPAT framework. We also explore the consequences of alternative trajectories for P, A and T, and we discuss the implications of these trajectories for reaching global goals based on our modelling. The findings are analysed in light of three theories in environmental sociology, each of which places a different emphasis on the different components of IPAT. We argue that the large amount of technological mitigation assumed in many forecasts makes affluence and population relatively irrelevant for climate change. However, we also consider it likely that both factors will be determinants of land use impact in the 21st century.