ABSTRACT
Projections of future climate build in ranges of uncertainty because of the difficulty of estimating future greenhouse gas concentrations, depending on what measures may be taken to reduce emissions, the simplifications involved in the techniques themselves, the limitations of the data they use, and uncertainties about how the climate system operates. The assumption behind the use of analogues is that, given similar background conditions, climate responds in a similar way to different forcing factors, so that as long as features such as the extent of land and sea and the pattern of ocean circulation remain the same, it makes no difference whether warming is due to changes in the concentration of greenhouse gases or in solar radiation. The most widely used technique for constructing future climate scenarios is the use of complex simulations of the atmosphere called General Circulation Models (GCMs).
