Greenhouse Gas Levels Hit Record High in 2025, UN Warns of Long-Term Climate Risks: Geneva, October 27 Global concentrations of the three major greenhouse gases reached unprecedented levels in 2025, intensifying concerns over rising temperatures, extreme weather and long-term climate change, according to the World Meteorological Organization (WMO).
In its latest Greenhouse Gas Bulletin, the United Nations weather agency reported that atmospheric concentrations of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) all climbed to new records. The findings highlight the continuing impact of fossil fuel consumption and the weakening ability of natural ecosystems to absorb carbon emissions.
The report comes ahead of the COP31 UN climate summit in Antalya, Türkiye, scheduled for November 9–20, 2026, where countries are expected to discuss measures to accelerate climate action and reduce emissions.
Highlights
- CO₂ reached 426.8 parts per million (ppm) in 2025, approximately 153% of its pre-industrial level.
- Methane rose to 1,948 parts per billion (ppb), equivalent to 267% of its pre-industrial concentration.
- Nitrous oxide reached 339.1 ppb, or 126% of its pre-industrial level.
- Atmospheric CO₂ increased by 2.8 ppm during 2025, exceeding the average annual rise of 2.6 ppm recorded over the previous decade.
- CO₂ remains the dominant contributor to the warming influence of long-lived greenhouse gases.
- The WMO warned that accumulated greenhouse gases will continue influencing the global climate for decades and even centuries.
Three Major Greenhouse Gases Reach New Records
The WMO’s measurements show that the accumulation of heat-trapping gases in the atmosphere continues despite international efforts to transition towards cleaner energy systems.
Carbon dioxide remains the principal concern because it is released in large quantities through the burning of coal, oil and natural gas, as well as through deforestation and other land-use changes. Once released, a substantial portion remains in the atmosphere for a very long time.
Methane is emitted from sources including livestock, rice cultivation, landfills, fossil fuel production and natural wetlands. Although it remains in the atmosphere for a shorter period than CO₂, it has a powerful warming effect.
Nitrous oxide is associated with agricultural fertilisers, soil processes, industrial activities and the burning of biomass. It is a potent greenhouse gas that also contributes to the depletion of stratospheric ozone.
According to the WMO, CO₂ accounts for around 66% of the warming influence of the three major long-lived greenhouse gases, making reductions in carbon emissions central to efforts to slow climate change.
CO₂ Growth Slows, but the Overall Trend Remains Concerning
The annual increase in atmospheric carbon dioxide was smaller in 2025 than in the preceding year. Concentrations rose by 2.8 ppm, compared with a record increase of 3.6 ppm between 2023 and 2024.
Scientists attributed part of this moderation to the recovery of natural carbon sinks and a reduction in wildfire-related carbon emissions following the strong El Niño conditions of 2023–2024.
Forests, vegetation, soils and oceans absorb a significant proportion of the carbon dioxide released by human activities. However, their capacity to remove carbon from the atmosphere varies with temperature, rainfall, drought, fire and other environmental conditions.
The improvement in natural absorption during 2025 does not indicate that the climate crisis is easing. The annual rise in CO₂ remained above its average growth rate over the previous decade, while fossil fuel combustion continued adding substantial amounts of carbon to the atmosphere.
Scientists are also monitoring the possibility that future El Niño conditions could weaken the effectiveness of land and ocean carbon sinks, allowing atmospheric concentrations to increase more rapidly.
Why Greenhouse Gas Concentrations Matter
Greenhouse gas concentrations measure the amount of these gases present in the atmosphere, rather than the quantity emitted during a particular year.
This distinction is important because emissions accumulate over time. Even if annual emissions stop increasing, atmospheric concentrations can continue to rise as long as global emissions exceed the amount absorbed by natural systems.
The resulting buildup traps additional heat in the Earth’s climate system, contributing to higher average temperatures and increasing the risks of heatwaves, heavy rainfall, droughts, wildfires and rising sea levels.
The WMO has also highlighted that the past 11 years, from 2015 through 2025, were the warmest in the instrumental record. This sustained warming trend reinforces concerns about the long-term consequences of continued greenhouse gas accumulation.
Methane and Nitrous Oxide Need Greater Attention
While carbon dioxide dominates the long-term warming impact, scientists are increasingly emphasising the importance of tackling methane and nitrous oxide.
Approximately 65% of methane entering the atmosphere comes from human activities, including agriculture, waste management and fossil fuel operations, while natural sources such as wetlands account for the remainder.
Reducing methane leakage from oil and gas infrastructure, improving landfill management and adopting better agricultural practices could help limit its contribution to near-term warming.
Nitrous oxide presents a separate challenge because emissions are closely linked to food production and fertiliser use. Improving fertiliser efficiency, managing agricultural soils and reducing industrial emissions could help curb its accumulation.
Both gases require targeted policies alongside the broader transition away from fossil fuels.
Electricity Networks Face Another Climate Challenge
The WMO has also called for greater attention to less abundant gases associated with energy infrastructure, particularly sulphur hexafluoride (SF₆) and molecular hydrogen (H₂).
SF₆ is widely used in electrical equipment because of its excellent insulating and arc-quenching properties. However, it is an exceptionally powerful greenhouse gas, with a global warming potential approximately 24,300 times that of CO₂ over a 100-year period, according to the WMO. Its atmospheric lifetime exceeds 1,000 years.
As electricity networks expand to accommodate renewable energy and rising power demand, preventing SF₆ leakage and developing suitable alternatives are becoming increasingly important.
Scientists are also investigating rising atmospheric hydrogen concentrations. Hydrogen is not a major direct greenhouse gas in the same way as CO₂ or methane, but its presence can indirectly affect atmospheric chemistry and the lifetime of methane. The causes and consequences of its recent increase require further investigation.
Climate Action Faces a Narrowing Window
The WMO findings underline the gap between international climate commitments and the pace of change needed to stabilise the climate.
The UN Environment Programme’s Emissions Gap Report 2025 estimated that global warming over this century could reach approximately 2.3–2.5°C if countries fully implement their latest climate pledges, while current policies point towards around 2.8°C of warming. These are projections, not certain outcomes, and depend on future policies and emissions.
The estimates remain above the Paris Agreement’s goal of limiting warming to well below 2°C while pursuing efforts to keep it to 1.5°C above pre-industrial levels.
Governments face mounting pressure to reduce fossil fuel dependence, expand renewable energy, improve energy efficiency, protect forests and strengthen monitoring of greenhouse gas emissions.
COP31 in Türkiye will provide another opportunity for countries to translate climate commitments into concrete measures. The latest atmospheric measurements offer a clear warning: progress must be assessed not only through policy announcements but also through measurable reductions in emissions and the rate at which greenhouse gases accumulate.
The central message from the WMO is clear: greenhouse gases are continuing to build up, and their effects will outlast the immediate decisions that drive emissions today. Faster and sustained reductions are essential to limit additional warming and reduce risks to communities, ecosystems and economies worldwide.
Sources: World Meteorological Organization, Greenhouse Gas Bulletin No. 22 (2026); UN Environment Programme, Emissions Gap Report 2025.
