What is a greenhouse gas?
A greenhouse gas is any gas that absorbs heat radiating from the Earth's surface and holds it in the atmosphere. A simple definition: greenhouse gases act like a blanket around the planet.
That is the greenhouse gas meaning in science. Some of this effect is natural and keeps the Earth habitable.
The problem is the extra gas added by human activity, which thickens the blanket and warms the climate. So greenhouse gases are not good or bad in themselves; the amount is what matters.
What are the 7 greenhouse gases?
The GHG Protocol Corporate Standard, the method companies use to measure emissions, covers seven greenhouse gases. These are the gases a company counts when it reports its emissions.
| Greenhouse gas | Where it often comes from in Nigeria |
|---|---|
| Carbon dioxide (CO₂) | Burning diesel, petrol and gas in generators, vehicles and plants; clearing forests |
| Methane (CH₄) | Oil and gas venting and leaks, landfills and waste, livestock |
| Nitrous oxide (N₂O) | Fertiliser use and fuel combustion |
| Hydrofluorocarbons (HFCs) | Air conditioning and refrigeration |
| Perfluorocarbons (PFCs) | Some industrial processes |
| Sulphur hexafluoride (SF₆) | High-voltage electrical equipment |
| Nitrogen trifluoride (NF₃) | Electronics manufacturing |
The top four, for most companies, are carbon dioxide, methane, nitrous oxide and the fluorinated gases from air conditioning. These are the most common greenhouse gas examples, and the types of greenhouse gas you will meet in a Nigerian inventory.
Because each gas traps a different amount of heat, emissions are converted into one unit: tonnes of carbon dioxide equivalent, written tCO₂e. That lets a company add methane, nitrous oxide and the rest into a single total.
Is water vapour, ozone or nitrogen a greenhouse gas?
Water vapour and ozone are greenhouse gases; nitrogen and oxygen are not. NASA lists carbon dioxide, methane, ozone, nitrous oxide, chlorofluorocarbons and water vapour as greenhouse gases.
Yes, methane is a greenhouse gas, and so is carbon dioxide; both are on every list. Water vapour is a special case.
NASA describes it as a "feedback": it rises as the planet warms and amplifies warming caused by other gases, rather than starting it. That is why companies do not report water vapour. Nitrogen and oxygen make up most of the air but are on neither list, which makes nitrogen the usual answer to the exam question "which is not a greenhouse gas?"
What is the meaning of emission?
The emission meaning is simple: an emission is something released into the air. In climate and carbon accounting, emissions means greenhouse gases released by an activity, such as running a generator or flaring gas, measured in tonnes of CO₂e.
The word has other meanings in physics and medicine; this entry covers the climate sense. The carbon emission meaning is narrower: it usually means a carbon dioxide emission, though people often use "carbon emissions" loosely to mean all greenhouse gas emissions.
So what is emission in a company's report? Greenhouse gas emissions can be direct, from fuel you burn yourself, or indirect, from the electricity you buy or the goods your suppliers make.
Companies sort them into three scopes. Fugitive emissions are leaks and releases that escape without being burned, such as methane from oil and gas equipment.
Where do Nigeria's greenhouse gas emissions come from?
Mostly from land use and energy. Nigeria's 2024 National Inventory Document, submitted to the UNFCCC, reports that land use, land-use change and forestry is the highest-emitting sector, followed by energy, agriculture, waste and industry.
The inventory's main figures for 2022:
Total emissions
were 678,270 kt CO₂e, up 81% since 2000.
Carbon dioxide
made up around 70% of emissions throughout 2000 to 2022.
The energy sector
produced 29.4% of the total. Within it, fuel combustion accounted for 84.5% and fugitive emissions for the rest.
The inventory also notes that diesel and petrol are used to generate electricity in homes and businesses. That matches what companies find on their own sites: when a Nigerian bag manufacturer began organising its data, its hardest figure was the diesel its generator burned.
Why do greenhouse gases matter to Nigerian companies?
Because emissions are now a reporting requirement, not just a scientific topic. Under the FRC's amended roadmap, public interest entities report under IFRS S1 and S2 from 2028, and their greenhouse gas emissions are a core part of that disclosure.
SRG 1 expects Scope 1 and Scope 2 emissions to be disclosed, with Scope 3 following after a first-year relief. Measuring them is called carbon accounting.
To reduce greenhouse gas emissions, a company first has to measure them. Our guide to carbon accounting explains how, from setting a boundary to building figures an assurance provider can check.