Greenhouse gases (GHGs)

Greenhouse gases (GHGs) are atmospheric gases that absorb and re-emit infrared radiation, producing the greenhouse effect: a natural phenomenon that keeps the Earth warm enough for life. The problem is the rapid increase of these gases caused by human activity, which intensifies the effect and drives accelerated global warming and climate change.

What is the greenhouse effect?

The greenhouse effect is a natural process: solar radiation reaching the Earth is partly reflected back to space and partly absorbed by the surface, which then re-emits it as infrared radiation. GHGs absorb part of that infrared radiation and redirect it back towards the surface instead of letting it escape. This keeps the planet's average temperature around 15°C. Without it, the average surface temperature would be roughly -18°C.

Types of greenhouse gases and their sources

Each GHG has a different global warming potential (GWP), which measures how much heat it traps relative to carbon dioxide over a given period (usually 100 years, GWP100). The values below come from the IPCC Sixth Assessment Report (AR6, 2021). The main GHGs are:

• Carbon dioxide (CO₂): the reference gas (GWP of 1) and the most abundant human-made GHG. Mainly emitted by burning fossil fuels (coal, oil and natural gas), deforestation and cement production.
• Methane (CH₄): a much more potent but shorter-lived gas. AR6 gives a GWP100 of about 29.8 for fossil methane and 27 for biogenic methane. Main sources are livestock, rice cultivation, fossil fuel extraction and the decomposition of organic matter in landfills.
• Nitrous oxide (N₂O): with a GWP100 of about 273, it comes mainly from nitrogen fertilisers, fuel combustion and some industrial processes.
• Fluorinated gases: hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulphur hexafluoride (SF₆) and nitrogen trifluoride (NF₃). These synthetic gases are used in refrigeration, air conditioning and industry, have very high GWPs (thousands to tens of thousands) and persist for a long time.
• Water vapour (H₂O): a potent GHG, but its concentration depends directly on temperature, so it acts as a feedback rather than a primary driver of warming.

Because each gas warms the planet differently, emissions are converted into a single unit, CO₂ equivalent (CO₂e), by multiplying each gas by its GWP.

Impact of greenhouse gases on climate change

The rapid rise in GHG concentrations from human activity is intensifying the natural greenhouse effect. According to the IPCC, human influence has warmed the climate by roughly 1.1 to 1.3°C above pre-industrial levels, with consequences such as:

• Rising global temperatures: melting glaciers and polar ice, sea level rise, and more frequent and intense heatwaves, droughts, floods and storms.
• Ocean acidification: the oceans absorb CO₂, which lowers their pH and harms corals, molluscs and plankton.
• Biodiversity loss: shifting ecosystems put many species at risk.
• Effects on human health: heat and air pollution worsen respiratory and cardiovascular conditions.

Why measuring the carbon footprint matters

The carbon footprint measures the total GHGs emitted by an activity, product, organisation or person, expressed in CO₂e. Measuring it is essential to:

• Understand how human activities affect the climate.
• Identify the main emission sources and define reduction measures.
• Track progress over time.
• Compare the environmental performance of products, services and organisations.
• Comply with climate regulations and reporting obligations.

The carbon footprint is calculated with standardised methodologies, the most widely used being the Greenhouse Gas Protocol (GHG Protocol), which organises emissions into Scope 1, Scope 2 and Scope 3. The GHG Protocol is currently undergoing a major revision of its corporate standards, expected to be finalised over the coming years.

At Manglai we help companies measure their carbon footprint across all scopes and prepare their sustainability reporting. Discover how Manglai can help you.