3 GHG emissions from energy

Using different forms of energy leads to different global warming emissions impacts. These are described by the “emissions-intensity” of the fuel/energy carrier.

Data from DEFRA (2022) gives representative values for the emissions associated with using 1 unit of energy from each source. Here, the focus is on the final energy (see Section 2.1) being used. For example, there are emissions values given for use of electricity (a form of final energy) generated from coal (a form of primary energy) – we don’t need to work out how much coal was burned in the power station, we use the data final energy directly.

Here is an extract of relevant data – first, for liquid fuels:

Final energy source	Emissions	Unit
Aviation fuel	0.26	kgCO2e / kWh
Oil (liquid fuel for boilers)	0.29	kgCO2e / kWh
Diesel	0.26	kgCO2e / kWh
Petrol	0.24	kgCO2e / kWh

For solid fuels:

Final energy source	Emissions	Unit
Coal	0.34	kgCO2e / kWh
Solid biomass	0.01	kgCO2e / kWh

Gaseous fuels:

Final energy source	Emissions	Unit
Gas (natural gas)	0.20	kgCO2e / kWh

And electricity:

Final energy source	Emissions	Unit
Electricity	0.19	kgCO2e / kWh

Take care with energy units. You can convert Joule-based units to Wh-based units as in the table below. It can be convenient to remember that the units above “kgCO_2e/kWh” are equivalent to “tCO_2e/MWh”, “ktCO_2e/GWh”, or “MtCO_2e/TWh”.

1 TWh	= 3.6 PJ
1 GWh	= 3.6 TJ
1 MWh	= 3.6 GJ
1 kWh	= 3.6 MJ

Historically, another unit of energy called the “tonne of oil equivalent” (toe) was used. This corresponds roughly to the average energy content of a tonne of crude oil, but has a fixed value of 1 toe = 41686 MJ.