Emissions or emissions level  – The mass of methane emitted into the atmosphere usually expressed in million tons.

Emission factor – The average rate of emissions from a specific source such as a piece of equipment, a facility or a country.

Emission intensity – The ratio of the volume of methane emitted to the volume of natural gas produced (upstream) or transmitted and distributed (downstream) expressed as a percentage.

Fugitive methane emissions – Occur from leakages that are not intended, for example because of a faulty seal or leaking valve.

Vented methane emissions – Emissions that are the result of intentional releases, often for safety reasons, due to the design of the facility or equipment, or because of operational requirements, such as venting a pipeline for inspection or maintenance.

Incomplete flaring methane emissions – These occur when natural gas that cannot be used or recovered economically is burned instead of being sold or vented. The vast majority of the natural gas is converted into CO2 and water, but some portion may not be combusted and is released as methane into the atmosphere.

Super emitters – These are emission sources within a sector or subsector that account for the majority of measured or estimated emissions. Definitions vary as to how to categorise super-emitters: studies have suggested anything between the top 5-15% of sources.

Environment – while the gas industry has portrayed itself as the cleanest fuel (in relations to emissions in general and carbon in particular) it is s till a fossil fuel. Three specific problems have been raised in relation to environmental claims by the gas industry:

1. 1. Insufficient account of methane emissions from the gas chain – given that methane is a much more powerful greenhouse gas than carbon dioxide – may invalidate any claim to have advantages over coal.
   2. The claim that unconventional gas development involves greater emissions of methane, and also the use of harmful chemicals in the hydraulic fracturing process.
   3. More generally, the lack of any significant progress towards widespread CCS, presents a major obstacle to long term inclusion of gas (or any other fossil fuel) in decarbonizing energy balances. This lack of progress can lead to the conclusion that new gas-fired generation and infrastructure can lead to carbon ‘lock-in’, namely that unabated gas installations will be emitting carbon for the commercial life of their assets