Greenhouse Gas (GHG)
Greenhouse gases are atmospheric gases that trap infrared radiation and warm the Earth's surface. The six main GHGs covered by the Kyoto Protocol are carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF₆). The Kigali Amendment added nitrogen trifluoride (NF₃).
Greenhouse gases differ in their warming potency and atmospheric lifetime. CO₂ is the most abundant anthropogenic GHG and the reference gas for CO₂ equivalent calculations. It persists in the atmosphere for hundreds of years. Methane is shorter-lived (about 12 years) but much more potent per molecule. N₂O and synthetic gases (HFCs, PFCs, SF₆) have GWPs ranging from hundreds to tens of thousands.
In corporate carbon accounting, the most commonly reported GHGs are: CO₂ from fossil fuel combustion and industrial processes; CH₄ from natural gas systems, waste management, and agriculture; N₂O from combustion, fertilizer use, and industrial processes; and HFCs from refrigeration and air conditioning systems.
The GHG Protocol requires reporting all seven Kyoto gases. Most emission factors already incorporate multiple gases and express results in CO₂e, but for certain sources (like refrigerant leaks), companies must separately quantify the specific gas released and apply its GWP.
Understanding the specific gases involved matters for reduction strategies. Methane reductions offer outsized near-term climate benefits due to methane's high GWP and short atmospheric lifetime. HFC phase-downs under the Kigali Amendment are driving refrigerant transitions that require careful tracking in carbon inventories.
Frequently asked questions
What are greenhouse gases? +
Greenhouse gases are atmospheric gases that trap heat and warm the Earth. The seven main GHGs under the Kyoto Protocol are CO₂, methane (CH₄), nitrous oxide (N₂O), HFCs, PFCs, SF₆, and NF₃. Each has a different global warming potential (GWP) reflecting its warming potency.
Which greenhouse gas has the highest GWP? +
Sulfur hexafluoride (SF₆) has the highest GWP at 25,200 over 100 years. However, it is emitted in very small quantities. Among commonly emitted gases, some HFC refrigerants have GWPs of 1,000–4,000, making refrigerant leak tracking important for carbon inventories.
Related terms
tCO₂e (Tonnes of CO₂ Equivalent)
tCO₂e — tonnes of carbon dioxide equivalent — is the standard unit for expressing greenhouse gas emissions. It normalizes different greenhouse gases (methane, nitrous oxide, HFCs, etc.) to their equivalent warming impact relative to CO₂ using global warming potentials (GWPs), allowing them to be summed into a single comparable metric.
Global Warming Potential (GWP)
Global warming potential (GWP) is a metric that compares the warming effect of a greenhouse gas relative to CO₂ over a specified time horizon, typically 100 years (GWP-100). It is published by the IPCC and used to convert different greenhouse gases into CO₂ equivalent for emissions inventories.
Carbon Accounting
Carbon accounting is the systematic process of measuring, recording, and reporting the greenhouse gas (GHG) emissions produced by an organization, product, or activity. It follows standardized methodologies — most commonly the GHG Protocol — to quantify emissions across Scope 1 (direct), Scope 2 (purchased energy), and Scope 3 (value chain) categories, producing an auditable inventory that underpins disclosure, reduction planning, and regulatory compliance.
Scope 1 Emissions
Scope 1 emissions are direct greenhouse gas emissions from sources that an organization owns or controls. This includes combustion of fossil fuels in owned boilers, furnaces, and vehicles; process emissions from manufacturing; and fugitive emissions such as refrigerant leaks and methane from owned landfills.