DEFINITION: The table refers to total primary energy supply (TPES). TPES equals production plus imports minus exports minus international marine bunkers plus or minus stock changes. The IEA energy balance methodology is based on the calorific content of the energy commodities and a common unit of account. The unit of account adopted is the tonne of oil equivalent (toe) which is defined as 107 kilocalories (41.868 gigajoules). This quantity of energy is, within a few per cent, equal to the net heat content of 1 tonne of crude oil. The difference between the "net” and the "gross” calorific value for each fuel is the latent heat of vaporisation of the water produced during combustion of the fuel. For coal and oil, net calorific value is about 5% less than gross, for most forms of natural and manufactured gas the difference is 9-10%, while for electricity there is no difference as the concept has no meaning in this case. The IEA balances are calculated using the physical energy content method to calculate the primary energy equivalent. The forecasts provided in the table refer to the Reference Scenario of the World Energy Outlook. The Reference Scenario projects supply and demand if present policies were to continue. The World Energy Outlook also presents a scenario for stabilising greenhouse gas concentrations at 550 parts per million (ppm) of CO2-equivalent (which would limit the temperature increase to about 3°C) and another scenario at 450 ppm of CO2-equivalent (which would limit the temperature increase to about 2°C).