Greenhouse Gas Levels Reached New Records in 2025, UN Weather Agency Says

The three main heat-trapping gases in Earth’s atmosphere all reached record concentrations in 2025, the World Meteorological Organization said on Tuesday, in its annual assessment released two weeks before the next United Nations climate summit.

Carbon dioxide averaged 426.8 parts per million last year, about 153 percent of its level before the industrial era began around 1750, according to the agency’s Greenhouse Gas Bulletin as reported by CBS News, UN News and Phys.org. Methane reached about 1,948 parts per billion, roughly 267 percent of the pre-industrial level, and nitrous oxide reached about 339.1 parts per billion, about 126 percent.

Carbon dioxide rose by 2.8 parts per million from 2024 to 2025. That was a smaller jump than the year before, when the increase was about 3.5 parts per million, the largest on record. The WMO attributed the slowdown partly to natural factors: forests and soils absorbed more carbon, and wildfire emissions fell, after the strong El Niño of 2023 and 2024 ended.

Scientists at the agency stressed that a slower increase is still an increase. Oksana Tarasova, a senior WMO scientific officer, said in remarks carried by CBS News and Phys.org that a 2.8 part-per-million rise remains a substantial addition of carbon to the atmosphere from burning fossil fuels. Ko Barrett, the WMO’s deputy secretary-general, summed up the findings as another year with another new record.

The longer view shows the scale of the change. When the bulletin was first published, in 2004, carbon dioxide stood at about 377.5 parts per million. The annual rate of increase has roughly tripled since the 1960s, according to UN News and Phys.org. About half of the carbon dioxide emitted each year stays in the atmosphere, with land and oceans absorbing the rest.

The report also flagged smaller contributors. Sulfur hexafluoride, an industrial gas that lingers for more than a thousand years, posted a record increase in 2025. Molecular hydrogen is also rising and has an indirect warming effect.

The agency expects concentrations to climb again in 2026, driven by continued fossil fuel use and a developing El Niño. The past 11 years have been the warmest on record, Ms. Barrett said.

An important caveat: the bulletin measures how much of each gas has built up in the air, not how much was emitted in a given year. A record concentration therefore reflects the long accumulation of past emissions, and it can be set even in a year when the pace of increase slows. Some observers will read the slower 2025 rise as a hopeful sign; the WMO’s own explanation credits mostly natural swings rather than cuts in emissions.

The findings are meant to inform negotiators at COP31, the UN climate conference scheduled for Nov. 9 to 20 in Antalya, Turkey.