CO₂ Equivalent

CO₂ equivalent (CO₂e) is a standardised unit used to express the climate impact of any greenhouse gas (GHG) in relation to carbon dioxide (CO₂), which serves as the reference point. In other words, CO₂e is the amount of CO₂ that would produce the same warming effect as a given amount of another GHG over a defined period, normally 100 years.

Greenhouse gases and the greenhouse effect

The greenhouse effect is a natural process that keeps the Earth at a temperature suitable for life. However, human activity has increased the concentration of greenhouse gases in the atmosphere, intensifying this effect and accelerating climate change.

The main GHGs covered by the Kyoto Protocol and the Paris Agreement are:

• Carbon dioxide (CO₂)
• Methane (CH₄)
• Nitrous oxide (N₂O)
• Hydrofluorocarbons (HFCs)
• Perfluorocarbons (PFCs)
• Sulphur hexafluoride (SF₆)
• Nitrogen trifluoride (NF₃)

How is CO₂ equivalent calculated?

CO₂e is calculated by multiplying the amount of each GHG by its Global Warming Potential (GWP), the factor that indicates how much heat a gas traps in the atmosphere compared with CO₂ over a chosen time horizon (usually 100 years).

The GWP values come from the IPCC. Under its latest assessment report (AR6, 2021), the 100-year values are CO₂ = 1, fossil methane = 29.8, biogenic methane = 27.0 and nitrous oxide = 273. Older reports gave lower figures (for example a methane GWP of 25 in AR4), so it is essential to state which version you apply.

Example: using the AR6 value, one tonne of fossil methane has the same climate impact as roughly 29.8 tonnes of CO₂ over 100 years. The calculation is simply: tonnes of CH₄ × 29.8 = tonnes of CO₂e.

Why CO₂ equivalent matters

• Comparing different GHGs: converting every gas into CO₂e makes their relative impact directly comparable.
• Setting reduction targets: CO₂e lets companies and governments define goals that cover all greenhouse gases, not just CO₂.
• Prioritising action: understanding the CO₂e of each source helps focus on the most effective measures.
• Communicating clearly: a single, easy-to-grasp metric improves transparency and public understanding.

CO₂ equivalent and the GHG Protocol

The Greenhouse Gas Protocol, developed by the World Resources Institute (WRI) and the World Business Council for Sustainable Development (WBCSD), is the leading international framework for corporate GHG inventories. It uses CO₂e as the standard reporting unit and is referenced by standards such as ISO 14064.

Expressing emissions in CO₂e is the foundation of transparent, comparable reporting. At Manglai we help companies measure their carbon footprint and prepare their sustainability reporting. Discover how Manglai can help you.