Global concentrations of carbon dioxide, methane and nitrous oxide reached unprecedented levels in 2025, strengthening concerns about the planet’s long-term warming trajectory, according to a new report from the World Meteorological Organization (WMO).
The report, released on October 27, found that the global average concentration of carbon dioxide reached 426.8 parts per million in 2025. That is approximately 53% above the pre-industrial level recorded before large-scale industrialisation.
Methane reached 1,948 parts per billion, equivalent to 167% of its pre-industrial level, while nitrous oxide rose to 339.1 parts per billion, or 26% above its pre-industrial baseline.
The findings highlight a central challenge in climate policy: even as governments discuss emissions reductions and clean-energy transitions, the atmospheric concentration of heat-trapping gases continues to rise.
Why atmospheric concentrations matter
Greenhouse gases absorb heat and help retain it in the atmosphere. Human activities, particularly the burning of fossil fuels, industrial processes and agriculture, have increased the quantities of these gases in the atmosphere.
Carbon dioxide is especially important because it remains in the climate system for a long time. The WMO says its continued accumulation commits the planet to additional long-term warming, even as countries work to reduce future emissions.
Methane is another major concern because it is a powerful heat-trapping gas, while nitrous oxide is associated with activities including agriculture and fertiliser use. Tackling climate change therefore requires action across energy, transport, industry, land use and food production rather than relying on a single solution.
The report also shows why annual emissions figures and atmospheric concentrations should not be confused. Emissions describe the gases released during a period; concentration measures how much has accumulated in the atmosphere. Concentrations can continue rising when human activities add more greenhouse gases than natural systems remove.
A challenge ahead of the next climate summit
The findings arrive shortly before the United Nations climate conference, COP31, scheduled for November 9–20 in Antalya, Türkiye. The meeting will provide governments with another opportunity to assess climate commitments and negotiate measures to limit global warming.
The WMO’s measurements offer a clear scientific benchmark for that debate. Announced targets alone cannot reverse the rise in atmospheric greenhouse gases; the trajectory depends on real changes in emissions and the balance between sources and natural carbon sinks.
For policymakers, the task is to accelerate reductions while improving monitoring and strengthening adaptation to climate impacts already being experienced. For countries vulnerable to heat, floods, droughts and rising seas, the continued accumulation of greenhouse gases adds urgency to both mitigation and preparedness.
The latest figures do not mean that every climate outcome is predetermined. They do show that the atmosphere has yet to register a reversal in the long-term build-up of the major greenhouse gases.
The central question for governments is whether policies and investments can deliver emissions cuts quickly enough to change that trajectory.
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