Optimizing energy transition paths in CO 2 emission reduction strategies

Abstract

In the consideration of energy use scenarios designed to avoid excessive build-up of atmospheric carbon dioxide and the effects of the associated climatic changes it can be anticipated that difficulties will ensue if needed rates of increased deployment of non-fossil fuel burning energy plants become very large. This may result if allowable maximum CO 2 concentrations are set sufficiently low, or if acceleration of non-fossil fuel energy use is sufficiently delayed. In a broad ranging numerical investigation of this problem, Perry et al. 1 have suggested that difficulty will be experienced in the transition to a non-fossil based economy, not only if the rate of growth of non-fossil fuel energy use rate, E ̇ N is excessive, but also if the second derivative, E ̈ N , becomes too large. This observation has important ramifications, since E ̈ N may exceed tolerable limits, whilst E ̇ N still remain modest in size. In making the estimates an empirical method for joining early and asymptotic energy use rates was employed. In order to make sure that the conclusions reached were not sensitive to the ad hoc nature of this technique, we have introduced a more rigorous approach by using a variational interpolation approach that minimizes the peak value of E ̈ N (or a combination of E ̈ N and E ̈ N . E ̇ N We find that such an optimization procedure can reduce the maximum values of E ̈ N by as much as 50% from those calculated by Perry et al. This indicates that the energy transition process should be easier that concluded by them, at least as far as a criterion based upon E ̈ N variation is concerned, but can still create difficulties, especially if a 500 ppmv CO 2 ceiling is considered hazardous and if actions to reduce fossil fuel use are delayed too long.