Earth’s atmospheric carbon dioxide (CO₂) concentration reached a record high of 430.2 parts per million (ppm) in May 2025, the highest level seen in millions of years, according to data collected at the Mauna Loa Observatory in Hawaii by NOAA and the Scripps Institution of Oceanography.
This level marks an increase of 3.5 ppm from May 2024’s 426.7 ppm.
Scientists link the steady rise in CO₂ primarily to the burning of fossil fuels, which continues to drive global warming and climate change.
This increase is fueling more extreme weather events such as heatwaves, droughts, intense rainfall, and flooding, as well as causing ocean acidification that threatens marine ecosystems.
The current CO₂ levels have not been seen on Earth for at least 3 to 5 million years, possibly since the Pliocene epoch, and some estimates suggest it could be as long as 30 million years.
The rapid rise in CO₂ is alarming because it reflects humanity’s failure to sufficiently curb emissions, pushing the planet toward warming levels beyond the Paris Agreement targets of 1.5°C to 2°C, which would exacerbate climate impacts.
The Mauna Loa Observatory’s measurements are considered the global benchmark for atmospheric CO₂, although regional variations exist.
The Earth’s CO₂ levels have now surpassed 430 ppm, a milestone not seen in millions of years, driven by fossil fuel emissions, and this trend is intensifying climate change and its associated environmental risks.