The following definitions reflect those used by the International Energy Agency (IEA); definitions used by other organisations and publications may vary.


sectoral agreement


steam-assisted gravity drainage




synthetic crude oil


Standing Group on Emergency Questions (of the IEA)


Standing Group on Global Energy Dialogue (of the IEA)


synthetic natural gas


sulphur dioxide


solid oxide fuel cells


Standing Group on the Oil Market (of the IEA)


short-run marginal cost


sport-utility vehicle


sovereign wealth funds


synthetic fuel


synthetic gas


for World Energy Outlook

- The Current Policies Scenario assumes no changes in policies from the mid-point of the year of publication (previously called the Reference Scenario).

- The New Policies Scenario – the World Energy Outlook's central scenario A scenario in the World Energy Outlook which takes account of broad policy commitments and plans that have been announced by countries, including national pledges to reduce greenhouse-gas emissions and plans to phase out fossil-energy subsidies, even if the measures to implement these commitments have yet to be identified or announced.

- 450 Scenario sets out an energy pathway that is consistent with a 50% chance of meeting the goal of limiting the long-term increase in average global temperature to 2 °C compared with pre-industrial levels.

for Energy Technology Perspectives

- The 6°C Scenario (6DS) is largely an extension of current trends. By 2050, energy use almost doubles (compared with 2009) and total greenhouse gas (GHG) emissions rise even more. In the absence of efforts to stabilise atmospheric concentrations of GHGs, average global temperature rise is projected to be at least 6°C in the long term. The 6DS is broadly consistent with the World Energy Outlook Current Policy Scenario.

- The 4°C Scenario (4DS) takes into account recent pledges made by countries to limit emissions and step up efforts to improve energy efficiency. It serves as the primary benchmark in Energy Technology Perspectives when comparisons are made among scenarios. Projecting a long-term temperature rise of 4°C, the 4DS is broadly consistent with the World Energy Outlook New Policies Scenario. In many respects, this is already an ambitious scenario that requires significant changes in policy and technologies. Moreover, capping the temperature increase at 4°C requires significant additional cuts in emissions in the period after 2050.

- The 2°C Scenario (2DS) is the focus of Energy Technology Perspectives and its related publications. The 2DS describes an energy system consistent with an emissions trajectory that recent climate science research indicates would give an 80% chance of limiting average global temperature increase to 2°C. It sets the target of cutting energy-related CO2 emissions by more than half in 2050 (compared with 2009) and ensuring that they continue to fall thereafter. Importantly, the 2DS acknowledges that transforming the energy sector is vital, but not the sole solution: the goal can only be achieved provided that CO2 and other GHG emissions in non-energy sectors are also reduced. The 2DS is broadly consistent with the World Energy Outlook 450 Scenario.

The 450 Scenario sets out an energy pathway consistent with the goal of limiting the global increase in temperature to 2°C by limiting concentration of greenhouse gases (GHGs) in the atmosphere to around 450 parts per million of CO2-equivalent.

smart grid

an electricity network that uses digital and other advanced technologies to monitor and manage the transport of electricity from all generation sources to meet the varying electricity demands of end users. Smart grids co-ordinate the needs and capabilities of all generators, grid operators, end users and electricity market stakeholders to operate all parts of the system as efficiently as possible, minimising costs and environmental impacts while maximising system reliability, resilience and stability.

smart meters

The European Smart Meters Industry Group defines four minimum functionalities of a smart meter: remote reading, two-way communication, support for advanced tariffing and payment systems, and remote disablement and enablement of supply. 

spot prices

the price that is quoted for immediate settlement of a transaction.

steam coal

all other hard coal that is not classified as coking coal. Also included are recovered slurries, middlings and other low-grade coal products not further classified by type. Coal of this quality is also commonly known as thermal coal.


as monitored by the IEA, any government action directed primarily at the energy sector that lowers the cost of energy production, raises the price received by energy producers or lowers the price paid by energy consumers.


a synthetic gas primarily composed of hydrogen and carbon monoxide produced by a chemical process.

synthetic fuels

any liquid fuel obtained from coal, natural gas or biomass. The best known process is the Fischer-Tropsch synthesis. An intermediate step in the production of synthetic fuel is often syngas, a mixture of carbon monoxide and hydrogen produced from coal which is sometimes directly used as an industrial fuel.


short ton