What happened
The World Meteorological Organization (WMO) published its yearly Greenhouse Gas Bulletin on 27 October 2026, ahead of the COP31 climate talks in Antalya, Türkiye, from 9 to 20 November. Its press release reports that the three main long-lived greenhouse gases all reached new highs in 2025:
- Carbon dioxide: a global average of 426.8 parts per million (ppm), 153% of the 1750 level. It rose 2.8 ppm on 2024, less than the 3.6 ppm jump the year before but above the average for 2011 to 2020. When the Bulletin started in 2004 the figure was 377.5 ppm.
- Methane: 1,948 parts per billion (ppb), 267% of the 1750 level. WMO says about 65% of methane comes from human sources such as cattle, rice, fossil fuels and landfill.
- Nitrous oxide: 339.1 ppb, from fertiliser, biomass burning and industrial processes as well as natural sources.
WMO singled out two smaller gases linked to the electricity system. The increase in sulphur hexafluoride (SF6), used as an insulating gas in switchgear, was a record in 2025, and WMO says it has risen steadily with electrification. It also flagged hydrogen leaks: hydrogen is not a greenhouse gas itself, but WMO says it has a strong indirect effect on warming. "Another year, another new record," said WMO Deputy Secretary-General Ko Barrett.
WMO expects concentrations to rise again in 2026, citing continued fossil fuel burning and a developing El Niño. The Bulletin measures what has built up in the air, not each year's emissions; for those, see our story on the UN Emissions Gap Report.
What the 2.8 ppm rise means in tonnes
Parts per million are hard to picture, so we converted them. The Global Carbon Budget, the scientific team that tracks the world's carbon each year, uses 2.124 billion tonnes of carbon for each 1 ppm of CO2, and each tonne of carbon is 3.664 tonnes of CO2. So:
- 2.8 ppm × 2.124 × 3.664 = about 21.8 billion tonnes of CO2 added to the atmosphere in 2025 and still there at the end of the year.
That is our calculation, not a WMO figure, and it is the net build-up after oceans and land took their share, which is why it is lower than the world's total emissions.
What it means for your business
The Bulletin does not change any reporting rule. What it does show is that the gases other than CO2 matter, and those are the ones businesses most often leave out. A UK carbon report covers the seven Kyoto gases, and the government factors convert each into CO2 equivalent. In the DESNZ 2026 set:
- 1 kg of methane = 28 kg CO2e
- 1 kg of nitrous oxide = 265 kg CO2e
- 1 kg of SF6 = 23,500 kg CO2e
Those are the IPCC's Fifth Assessment values. WMO quotes the newer value for SF6, about 24,300. Both are right for their purpose: UK reports use the DESNZ set, and our post on AR5 and AR6 values explains why.
If your site has its own high-voltage supply (a factory, a large warehouse, a campus or a data centre with its own substation or ring main unit), SF6 that leaks from switchgear you own or control is a Scope 1 emission. Most smaller firms take power at low voltage, and the network operator's switchgear is not theirs to report. Our story on the DESNZ SF6-free switchgear report covers the UK position.
A worked example
An engineer services a site's own 11kV switchgear and tops it up with 2 kg of SF6 (an illustrative figure):
| Basis | Factor | kg CO2e |
|---|---|---|
| DESNZ 2026 (use this in a UK report) | 23,500 kg per kg | 47,000 |
| WMO's quoted value (for comparison only) | 24,300 kg per kg | 48,600 |
At the DESNZ factor, the top-up is 47.00 tonnes CO2e, the same as about 358,888 kWh of UK grid electricity at the 2026 factor of 0.13096 kg per kWh.
What to do now
- If you own HV switchgear: ask your maintenance contractor for the kilograms of SF6 added at each service and keep the records. Gas added to top up equipment is the usual way to estimate what leaked.
- If you have air conditioning or refrigeration: do the same for refrigerant top-ups, which are the most common non-CO2 emission in a business report.
- If you farm, run landfill or handle gas: check that methane and nitrous oxide are in your report, not only fuel and electricity.
- Everyone: say which factor set you used, so a reader can tell AR5 figures from AR6 figures.
