Greenhouse gases: which ones they are, sources and how they are measured

Greenhouse gases (GHG) are the gases in the atmosphere that trap part of the heat the Earth radiates back to space, causing the greenhouse effect. At natural concentrations they make the planet habitable, but their increase due to human activity is the cause of global warming. For inventory and regulatory purposes, seven gases are accounted for: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphur hexafluoride (SF6) and nitrogen trifluoride (NF3).

They do not all warm equally. To be able to add them up, each gas is converted into CO2 equivalent using its global warming potential, which compares how much heat it traps relative to CO2 over a time horizon, usually 100 years.

Which the greenhouse gases are

These seven gases are the ones covered by national inventories and carbon footprint calculation standards. The first three are the most abundant in emissions; the four fluorinated gases are far less frequent but have an extremely high warming potential.

Global warming potential (GWP)

The global warming potential (GWP) expresses how many times more heat a gas traps than CO2 over 100 years. The table below gives 100-year orders of magnitude: the exact values depend on which IPCC assessment report is applied (AR5 or AR6) and, for HFCs and PFCs, these are families of compounds whose values differ widely. That is why any report should state which set of values was used.

Exact values are updated with each IPCC report, so it is best to always state the version used when reporting.

Main sources by gas

Each gas is linked to different activities, which helps identify where to act:

• CO2: the most abundant gas. It comes mainly from burning coal, oil and gas for energy, transport and industry, and from processes such as cement manufacturing.
• CH4: generated by livestock (enteric fermentation), rice paddies, landfills and leaks in the production and transport of natural gas.
• N2O: comes mainly from the use of nitrogen fertilisers in agriculture and from some industrial processes.
• Fluorinated gases (HFCs, PFCs, SF6, NF3): of industrial origin. They are used in refrigeration, electrical insulation, aluminium production or semiconductor manufacturing.

How greenhouse gases are measured

Measuring an organisation's emissions means calculating its carbon footprint. In practice, most emissions are not measured directly with sensors but estimated by multiplying an activity figure (litres of fuel, kWh of electricity, kilometres travelled) by an emission factor that translates that activity into emissions. You can see the full procedure in our guide on what the carbon footprint is and how it is calculated.

Scopes 1, 2 and 3

To organise emissions, the standards classify them into three scopes:

• Scope 1: direct emissions from owned sources, such as boilers or the vehicle fleet.
• Scope 2: indirect emissions from purchased energy, mainly electricity.
• Scope 3: the rest of the indirect value-chain emissions, from suppliers to product use.

If you want to go deeper into the difference between them, we develop it in the article on scope 1, 2 and 3 emissions.

The measurement framework

The calculation relies on international frameworks. The GHG Protocol is the most widespread accounting standard, and ISO 14064-1:2018 offers a certifiable framework. Both trace their roots to the Kyoto Protocol, which established the basket of gases accounted for today; NF3 was added in its second commitment period. The result is always expressed in tonnes of CO2 equivalent so that different gases can be aggregated into a single figure.

Why these gases matter for companies

Beyond climate science, measuring greenhouse gases has become a practical obligation for many organisations. In Spain, Royal Decree 214/2025 requires companies within its scope to calculate their scope 1 and scope 2 carbon footprint (scope 3 remains voluntary) and to have a reduction plan with a five-year horizon and quantified targets. Registering the footprint with the MITECO carbon footprint registry, by contrast, remains voluntary for private companies. But even where it is not mandatory, measuring brings concrete benefits.

Knowing which gases a company emits and in what proportion makes it possible to prioritise actions. In most organisations, CO2 from energy and transport dominates the inventory, so the first levers are usually energy efficiency, switching to renewable electricity and optimising logistics. In specific sectors, however, the weight may lie in other gases: methane in livestock and landfills, nitrous oxide in agriculture or fluorinated gases in refrigeration and electronics.

Measuring rigorously also reduces the risk of greenwashing. Communicating reduction or neutrality targets without a solid inventory behind them exposes a company to accusations of green-washing and, increasingly, to regulatory consequences: the EU Empowering Consumers Directive (EU) 2024/825, which applies from 27 September 2026, bans generic environmental claims without substantiation and climate neutrality claims based on offsetting. A well-built inventory, by scope and with traceable emission factors, is the basis both for reporting and for making credible decisions.

Frequently asked questions

How many greenhouse gases are accounted for?

Inventories and calculation standards consider seven gases: CO2, CH4, N2O, HFCs, PFCs, SF6 and NF3. There are other gases with a greenhouse effect, such as water vapour or ozone, but they are not included in organisations' emissions accounting.

Why is everything converted into CO2 equivalent?

Because each gas traps a different amount of heat. Converting each one into CO2 equivalent using its warming potential makes it possible to add them up and express the carbon footprint in a single comparable unit.

Which is the most important greenhouse gas?

CO2 contributes the most to global warming because of its huge emission volume, although it is not the one with the highest potential per molecule. Methane has a much higher potential in the short term, and fluorinated gases reach values thousands of times that of CO2.

Measure your emissions rigorously and by scope

Knowing which gases you emit and where they come from is the first step; the next is measuring them well. With Manglai's carbon footprint software you can calculate your carbon footprint by scope, with up-to-date emission factors, and turn that data into an actionable reduction plan.