CO2 equivalent (CO2e) is a unit of measurement that expresses the impact of each greenhouse gas in terms of the amount of CO2.
Interesting notes on CO2 equivalent
- CO2 refers exclusively to carbon dioxide emissions, while CO2 equivalent includes the measurement of the impact of the different greenhouse gases considered in the CO2 equivalent value;
- The unit of measurement used for the carbon footprint is CO2 equivalent;
- Both the IPCC and the Greenhouse Gas Protocol have developed conversion tables to calculate the CO2 equivalent of various greenhouse gases.
Remember when you got the unit of measurement wrong in maths problems and your teacher told you that you can never compare apples with pears? Here, CO2 equivalent comes to the rescue as a standard unit.
Man-made climate change is caused by the release of greenhouse gases into the atmosphere. These gases are many and varied. Chief among the greenhouse gases is carbon dioxide or carbon dioxide (CO2), a gas that is emitted every time fossil fuels are burned. It is followed by methane gas (CH4), which is mainly produced by agricultural activities and landfills. Methane gas has a higher polluting capacity than CO2 in terms of the impact the two gases have on the climate over 100 years. Even more impactful in terms of climate change are refrigerant gases and nitrous oxide (N2O), released into the atmosphere in smaller quantities and mainly from industrial and agricultural processes.
A single element or activity can cause the emission of a combination of several different greenhouse gases in varying quantities. In such cases, the calculation of the carbon footprint could become quite complicated. In order to simplify the study of greenhouse gas emissions and to make emissions from different types of gases comparable, CO2 equivalent is used as the unit of measurement.
The United Nations Intergovernmental Panel on Climate Change (IPCC) has developed the Global Warming Potential (GWP), which is an index measuring the warming potential absorbed by a given quantity of a greenhouse gas in comparison with that absorbed by the same mass of CO2 over a given period of time, usually 100 years. By multiplying the mass of a greenhouse gas by its Global Warming Potential, we obtain the CO2 equivalent value of that mass of gas.
For example, the GWP of methane is 28, that of nitrous oxide is 265. So while one tonne of methane corresponds to 28 tonnes of CO2e, one tonne of nitrous oxide corresponds to 265 tonnes of CO2e.