Designing, modelling and analysing global emissions policies are becoming increasingly complex undertakings. Pressure on developing economies to make quantifiable emissions reduction commitments has led to the introduction of intensity based emissions targets, where reductions in emissions are specified with reference to some measure of output, generally gross domestic product. The Copenhagen commitments of China and India are two prominent examples. From a modelling perspective, intensity targets substantially increase the complexity of analysis, with respect to both theoretical design and computational implementation. Here, a clear and practically relevant theoretical design is used to present a new algorithm that can be applied to frameworks that model the complex interaction that occurs between emissions policy instruments, emissions levels and output effects under an emissions intensity target. The coding of the algorithm has been simplified to allow for easy integration into a range of modelling frameworks. Further development of the algorithm that allows for more complex theoretical design structures is possible.