tment cost per kW of capacity, although the competitive advantage over other technologies may be reduced by the higher cost of gas compared with coal or other fuel inputs. The choice of generating technology also affects the size and location of power plants and, consequently, the need for transmission capacity. Distributed generation plants located at an end user's site or at a local distribution utility, supplying power directly to the local distribution network, reduce the need to invest in long-distance high-tension transmission lines. Distributed generation technologies include engines, small turbines, fuel cells and photovoltaic systems. They represent a small share of the electricity market today, but the wide range of potential applications and favourable government policies for combined heat and power and for renewable energy technologies are expected to boost their market share over the coming decades (IEA, 2002). Improvements in the efficiency of end-use technology - to the extent that they are actually deployed - also affect electricity demand (see Section 4). Climatic conditions. Changes in climate, resulting from global warming and leading to marked changes in average ambient temperatures, could have a significant impact on electricity demand for cooling and heating purposes. The impact is likely to be greater for cooling, as the bulk of heating needs in most countries are met by other, more direct forms of energy, such as natural gas and oil products. Air conditioning is one of the leading drivers of electricity demand in many OECD countries and the richest developing economies. The rate of growth of demand will determine how much investment is needed in supply infrastructure. But there is no certainty that all of the investment needed is forthcoming. If actual investment falls short of that required or is delayed, some part of demand might go unmet, leading to temporary or persistent power shortages. The main uncertainties surrounding the adequacy of electricity investment worldwide relate to the 