Carbon dioxide levels in the atmosphere reached a record high in April, averaging 431 parts per million (ppm), according to data from the US National Oceanic and Atmospheric Administration’s Mauna Loa Observatory in Hawaii.
The observatory has been tracking atmospheric CO2 since 1958, when April levels stood at under 320 ppm.
Pre-industrial CO2 levels are estimated to have been at 280 ppm or below, with even warmer interglacial periods historically topping out at around 300 ppm.
The latest reading represents a significant and sustained departure from those baselines.
CO2 levels tend to peak in April each year as decaying plants release greenhouse gases following winter.
Some of that CO2 is reabsorbed by plants as they grow through warmer months. However, NOAA’s long-term data show average monthly CO2 levels rising steadily year on year.
Zachary Labe, climate scientist at Climate Central, described the record as “depressing” but not unexpected. He said it was “just another sign that carbon dioxide continues to increase in our atmosphere as our planet continues to warm.”
For many climate scientists, he added, it represented another record moving in the wrong direction.
The record comes as the observatory faces potential closure. A budget proposal for the 2027 fiscal year includes cuts to numerous climate monitoring facilities, including Mauna Loa.
The loss of the world’s longest-running direct CO2 monitoring record would represent a significant blow to climate science.
US emissions fell in 2023 and 2024 but rose again in 2025, partly driven by rising electricity demand from AI data centres.
Expansion of solar and wind energy is cited as a reason for cautious optimism.
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