in addition at the level of plants and units there is no evidence of any differences in the speed of energy technology change across a wide range of technologies since the nineteenth century wilson forthcoming policy has typically focused on technology as the main lever for reducing emissions and it is indeed a powerful driver future energy technology change will be as important for determining future greenhouse gas emissions levels as longterm demographic and economic developments over the course of the twentyfirst century roehrl and riahi figure illustrates the contributions of energy technologies to greenhouse gas emissions reductions under a highemissions baseline scenario required for stabilization at a concentration of ppmv co e by