Most conversations about climate change eventually land on one gas: carbon dioxide. It has become a kind of shorthand for the whole problem. That is fair, up to a point. CO2 does most of the heavy lifting. But it is not the whole story, and treating it as if it is can lead to strange decisions, from ignoring methane leaks on a farm to overlooking a fridge full of powerful refrigerant gases in a warehouse.
The point of this guide is to give you a clear, useful picture of the greenhouse gases that actually matter, what they do, an interesting fact or common misconception about each, and what the newest data tells us about where we stand.
Table of contents
Six groups of gases do almost all the work.
Carbon dioxide (CO2): the largest single driver, mostly from fossil fuels and land use.
Methane (CH4): much shorter-lived than CO2, but far more powerful tonne for tonne, from livestock, fossil fuels and waste.
Nitrous oxide (N2O): mainly from fertilisers and manure, small in volume, large in effect.
Fluorinated gases (HFCs, PFCs, SF6, NF3): synthetic, tiny in the atmosphere, but some are thousands of times more warming than CO2.
Water vapour: the strongest natural greenhouse gas, but not something we emit in a way that matters. It acts as an amplifier.
Ozone (in the lower atmosphere): a secondary greenhouse gas formed from other pollutants.
When a UK business measures its emissions properly, it does not just add up "carbon".
Carbon dioxide (CO2)
What it is. A colourless, odourless gas released when we burn fossil fuels, make cement, and clear or burn forests. It also cycles naturally through plants, soils and oceans.
What it does. CO2 absorbs heat that would otherwise escape to space and releases it back towards the surface. Individually, its warming effect per molecule is modest compared with methane or the fluorinated gases. Its influence is enormous because there is so much of it, and because a significant share of what we emit stays in the atmosphere for centuries.
The latest data. In 2024, the global average CO2 concentration reached 423.9 parts per million, an increase of 3.5 ppm on 2023 and 152% of pre-industrial levels according to the WMO Greenhouse Gas Bulletin published in October 2025. That single-year rise is the largest annual increase in the concentration of CO2 since global monitoring began. NOAA's monitoring network measured a 3.72 ppm jump between January 2024 and January 2025, a record. Monthly averages have continued to climb through 2026, passing 429 ppm in July.
An interesting fact. When the WMO's Greenhouse Gas Bulletin was first published in 2004, the global average CO2 concentration was 377.1 ppm. In twenty years it has risen by nearly 47 ppm, which is more than the total increase across the previous two hundred years combined.
A common misconception. People often assume that if we stopped emitting CO2 tomorrow, concentrations would fall back quickly. They would not. A meaningful fraction of the CO2 we have already emitted will stay in the atmosphere for hundreds to thousands of years. This is one of the reasons careful climate finance, alongside emissions reductions, matters. Reduction changes the emissions still to come. Verified carbon removals address carbon already in the air.
Methane (CH4)
What it is. A simple hydrocarbon, the main ingredient in natural gas. It is released when fossil fuels are extracted, from livestock digestion, from paddy fields, and from landfills and wastewater. For more focused explanation of farming practices that can address the agricultural sources of these greenhouse gases read our blog on Regenerative Farming: Principles, Practices, and Climate Benefits
What it does. Methane is a much stronger greenhouse gas than CO2 over short timescales. Using IPCC AR6 values, a tonne of fossil methane traps roughly 29.8 times as much heat as a tonne of CO2 over 100 years, and around 82 times as much over 20 years. It is also short-lived, breaking down in the atmosphere in about a decade. That combination matters: cutting methane emissions delivers relatively fast cooling benefits compared with cutting CO2.
The latest data. Global methane concentrations reached 1,942 parts per billion in 2024, which is 266% of pre-industrial levels, according to the WMO. The 2023 to 2024 rise was slightly smaller than the year before, and closer to the ten-year average, but it is still a rise. NOAA's more recent monthly data shows methane broadly flat through the first half of 2026.
An interesting fact. Methane is not just something cows produce. Roughly a third of human-driven methane emissions come from the fossil fuel industry itself, primarily from leaks in oil and gas infrastructure, according to UNEP's assessment work.
A common misconception. Because methane breaks down relatively quickly, some people conclude it is not really a problem. It is a big problem, precisely because its effect is concentrated in the near term. A methane leak is a fire in the room. CO2 is the smoke that stays after the fire is out. Both need attention. This is one of the reasons a serious carbon footprint calculation for a UK business should account for methane on both 20-year and 100-year timescales, not just the standard 100-year number.
Nitrous oxide (N2O)
What it is. A gas mostly emitted from farming: fertiliser use, manure management, and soil microbes responding to nitrogen inputs. Industrial processes and some transport also contribute.
What it does. Nitrous oxide is a long-lived, potent greenhouse gas, with a 100-year global warming potential of around 273 according to IPCC AR6. It also depletes stratospheric ozone. It is the third most important long-lived greenhouse gas after CO2 and methane.
The latest data. N2O reached 338.0 parts per billion in 2024, which is 125% of the pre-industrial level, according to the WMO Greenhouse Gas Bulletin. The 2024 rise, around 1 ppb, was close to the average of the last decade.
An interesting fact. Nitrous oxide is chemically the same gas dentists have used as an anaesthetic for over 150 years. In the atmosphere it stays around for approximately 116 years.
A common misconception. Because farming feels benign compared with a coal plant, its climate impact is often underestimated. In the UK, DESNZ's 2024 statistics show N2O accounts for around 6% of national greenhouse gas emissions on a CO2-equivalent basis, and methane around 15%. Agriculture is not a rounding error in a UK company's supply chain footprint.
Fluorinated gases (HFCs, PFCs, SF6, NF3)
What they are. A family of synthetic gases, invented in the twentieth century for refrigeration, air conditioning, insulation, electrical switchgear, and semiconductor manufacture.
What they do. These gases are present in the atmosphere in tiny quantities, measured in parts per trillion. Their power lies in how efficiently they trap heat and how long they persist.
Hydrofluorocarbons (HFCs) are widely used in refrigeration and air conditioning. Global warming potentials vary, but many common HFCs are hundreds to thousands of times more warming than CO2.
Sulphur hexafluoride (SF6) is used as an insulator in high-voltage electrical equipment. It has a 100-year global warming potential of around 23,500 and an atmospheric lifetime of roughly 3,200 years, according to the IPCC AR6 GWP tables and NOAA. Together those numbers make SF6 the most potent greenhouse gas we routinely emit.
Nitrogen trifluoride (NF3) is used in semiconductor and flat-panel display manufacturing, and has a 100-year GWP of around 17,200 with a lifetime of several hundred years.
The latest data. NOAA's SF6 monitoring recorded atmospheric concentrations of around 12.15 parts per trillion in April 2025, still rising at roughly 0.4 to 0.5 ppt per year. HFCs are being progressively phased down under the Kigali Amendment to the Montreal Protocol, with developed countries required to have cut consumption by 40% from baseline in 2024, rising to 85% by 2036.
An interesting fact. SF6 is used in electricity grids partly because it stops sparks jumping across switchgear at high voltages. In other words, it helps make the electricity system that decarbonises everything else possible. The industry is now actively developing alternatives, but the legacy is significant, and every kilogramme of SF6 that leaks is equivalent to about 23.5 tonnes of CO2.
A common misconception. People sometimes assume the ozone layer story is over. It is a real success, and the Montreal Protocol is one of the strongest examples of what international policy can achieve. But the substances that replaced CFCs, including many HFCs, turned out to be powerful greenhouse gases in their own right. Kigali is the follow-up, and it is a live piece of work through the 2030s and 2040s.
Water vapour
What it is. The gaseous form of water. It is the most abundant greenhouse gas in the atmosphere by far.
What it does. Water vapour absorbs and re-emits infrared radiation, like CO2 and methane, but more of it. By some accounting methods, it contributes two to three times more to the natural greenhouse effect than CO2, according to the IPCC. Without any water vapour or other greenhouse gases, the Earth would be a frozen rock.
Here is the important part. Human activity does not meaningfully control how much water vapour is in the atmosphere. Temperature does. Warmer air holds more moisture, following a physical relationship known as the Clausius-Clapeyron equation, roughly 7% more moisture per degree of warming. That is why scientists describe water vapour as a feedback, not a forcing. It amplifies whatever else is happening. When CO2 or methane warms the air, more water evaporates. That extra water vapour traps more heat. That warms the air more. And so on.
An interesting fact. Multiple studies estimate that this feedback roughly doubles the warming effect of CO2 alone. In other words, when you read that CO2 has warmed the planet by a certain amount, water vapour has quietly done about the same again on top.
A common misconception. A recurring argument online goes something like: "Water vapour is the main greenhouse gas, so CO2 does not matter." This gets the physics backwards. Water vapour is downstream of temperature, not upstream of it. If we cooled the planet, atmospheric water vapour would fall. The gases we actually control, mainly CO2 and methane, set the thermostat that water vapour then amplifies.
Ozone (in the lower atmosphere)
What it is. Ozone (O3) exists in two very different places. High in the stratosphere it protects life on Earth from ultraviolet radiation. In the lower atmosphere, near the surface, it is a pollutant, formed when nitrogen oxides and volatile organic compounds react in sunlight.
What it does. Tropospheric ozone is a greenhouse gas. It also damages plants and human lungs. It is not routinely reported in the same way as CO2 or methane, because it forms and dissipates on short timescales and varies enormously by location.
A common misconception. The stratospheric "ozone hole" is a different issue from the greenhouse effect, but the two are connected. The gases that once caused the ozone hole (CFCs) are also potent greenhouse gases, and their long-lived successors (many HFCs) are as well. This is why the Montreal Protocol's Kigali Amendment matters for climate policy, not just air quality policy.
Where the UK sits
The UK's 2024 territorial greenhouse gas emissions were provisionally estimated at 371 million tonnes of CO2 equivalent, a 4% fall on 2023 and roughly 54% below 1990 levels, according to DESNZ. The Climate Change Committee's 2025 report to Parliament confirmed this as the tenth consecutive year of sustained reductions, outside the pandemic years.
Break that down by gas and the picture is instructive. CO2 accounts for around 78% of the total. Methane sits at roughly 15%, nitrous oxide at 6%, and F-gases at around 1%. That last number is worth pausing on. F-gases are a small fraction of the total, but a very small mass of the most potent members can carry a very large climate cost. That is why they receive their own regulatory attention.
Why the distinctions matter for a business
None of this is trivia. When a UK business measures its emissions properly, it does not just add up "carbon". It works out how much of each gas is being emitted, from where, and then converts each into a common CO2-equivalent figure using accepted global warming potentials. That process is what makes a footprint honest.
Three practical implications sit behind the numbers above. First, CO2 dominates most business footprints, but not all of them. A dairy farm, a food manufacturer, or a landfill operator will find methane on the ledger. A refrigeration-heavy business or a large electrical grid asset owner will find F-gases. A fertiliser-intensive agricultural business will find nitrous oxide. Assuming everything is CO2 will mislead you.
Second, reducing methane and F-gases delivers relatively fast climate benefits because both are potent and the fluorinated group can be tackled by better containment, recovery and substitution. This is one of the few areas where the cost of action and the speed of climate effect line up neatly.
Third, verified carbon removals are not the same as avoidance credits. Removal projects draw CO2 out of the atmosphere and store it. Avoidance projects prevent emissions relative to a baseline. Both have a role, but they are not interchangeable. Anyone shopping for offsets should know which they are buying and why.
Read more about SBTI targets for UK Businesses.
CNB's view
At Carbon Neutral Britain™, we do not treat reduction and climate finance as sequential steps. Both should begin together. Reducing operational emissions changes the emissions still to come. Financing verified reductions and removals now addresses carbon that has already accumulated, and supports the projects and communities doing the practical work. Neither is a substitute for the other, and neither is a good excuse to delay the other.
We also think honest measurement should come before either. A carbon footprint that separates the gases properly, applies the correct global warming potentials, and covers the right scopes is the difference between a decision made on evidence and a decision made on hope. If you are just beginning that work, our carbon reduction plan service is designed to give a UK business a documented, tender-ready basis for what comes next.
A closing thought
The atmosphere does not care about our categories. It responds to physics. Every gas we have discussed above traps heat, in different quantities, over different timescales, with different origins. Treating them as one lump called "carbon" is convenient, and sometimes necessary for reporting. But it is not quite the truth.
The good news, if there is any to be found here, is that the picture is not mysterious. The gases are known. The measurements are careful. The direction of travel is difficult but not obscure. What remains is the ordinary, unglamorous work of measuring what we emit, reducing what we can, and paying honestly for what we cannot yet reduce. That work is happening, in Britain and elsewhere, and it deserves to be done well.
Carbon Neutral Britain™
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What are the main greenhouse gases?
The gases that matter most are carbon dioxide, methane, nitrous oxide and the fluorinated gases (HFCs, PFCs, SF6 and NF3). Water vapour is the strongest natural greenhouse gas but acts as a feedback rather than something humans emit directly.
Which greenhouse gas is the worst?
Why is methane sometimes described as more powerful than CO2?
Because tonne for tonne it traps far more heat. Its 100-year global warming potential is roughly 30, and its 20-year value is roughly 80. It is also much shorter-lived, which is why cutting methane produces relatively rapid climate benefits.
Is water vapour more important than CO2?
Water vapour contributes more to the natural greenhouse effect, but its concentration in the atmosphere is controlled by temperature, not by direct emissions. It amplifies warming caused by gases we do emit. CO2 and methane set the thermostat that water vapour then responds to.
How much have greenhouse gases increased?
According to the WMO, in 2024 CO2 was at 152% of pre-industrial levels, methane at 266%, and nitrous oxide at 125%. These are the highest concentrations recorded in modern monitoring.
