Greenhouse gas levels hit record highs in 2025, UN warns

Greenhouse gas concentrations in the atmosphere reached record levels in 2025, raising concerns about further global warming and long-lasting climate damage, the United Nations has warned.

The World Meteorological Organisation (WMO) said concentrations of the three main greenhouse gases — carbon dioxide, methane and nitrous oxide — continued to rise last year. The increase is expected to contribute to further temperature rises and intensify climate-related risks for decades and centuries.

The findings were published in the WMO’s annual Greenhouse Gas Bulletin ahead of the COP31 UN climate summit, scheduled to take place in Antalya, Türkiye, from November 9 to 20.

WMO Deputy Secretary-General Ko Barrett said greenhouse gases were trapping an unprecedented amount of heat in the atmosphere. This was increasing the energy available for extreme weather events and creating growing risks for economies and societies.

She warned that the past 11 years had been the warmest on record and that the trend was likely to continue. Carbon dioxide remains a particular concern because it stays in the atmosphere for a long time, affecting the climate for decades and even centuries.

According to the report, atmospheric carbon dioxide concentrations reached 426.8 parts per million in 2025. Methane levels stood at 1,948 parts per billion, while nitrous oxide reached 339.1 parts per billion.

These figures were equivalent to 153%, 267% and 126% of their respective pre-industrial levels recorded before 1750.

Carbon dioxide accounts for around 66% of the warming effect caused by long-lived greenhouse gases. Approximately half of the carbon dioxide released each year remains in the atmosphere, while the remainder is absorbed by land and oceans.

The global average concentration of carbon dioxide increased by 2.8 parts per million between 2024 and 2025. Although this was below the record rise of 3.6 parts per million recorded between 2023 and 2024, it remained above the average annual increase of 2.6 parts per million over the past decade.

The WMO attributed the smaller increase partly to the recovery of land-based carbon sinks and lower carbon emissions from fires in 2025. These changes followed the strong El Niño event of 2023 and 2024, which contributed to warmer conditions.

However, WMO senior scientific officer Oksana Tarasova stressed that the annual increase remained substantial, largely because of fossil fuel consumption.

She also warned that greenhouse gas concentrations could rise further in 2026 as coal, oil and gas use continues and a powerful El Niño develops. Such conditions could weaken the ability of land ecosystems to absorb carbon dioxide.

Methane is responsible for around 16% of the warming effect of long-lived greenhouse gases. It remains in the atmosphere for less time than carbon dioxide but is a powerful contributor to global warming. Natural sources, including wetlands, account for about one-third of methane emissions, while human activities such as livestock farming, rice cultivation, landfills and biomass burning produce much of the remainder.

The WMO report also highlighted concerns about less abundant gases linked to electricity systems. It called for greater attention to molecular hydrogen and sulfur hexafluoride as countries move towards cleaner energy.

Sulfur hexafluoride is used in electricity distribution equipment to prevent electrical sparks. Its atmospheric concentration has increased steadily over the past three decades, adding to concerns about the climate impact of industrial gases.

The findings underline the continuing challenge of limiting global warming as greenhouse gas concentrations keep reaching new highs despite international efforts to reduce emissions.