FALSE: Atmospheric carbon dioxide was not 345ppm in 2025
A claim that atmospheric carbon dioxide (CO₂) stood at 345ppm in 2025 is FALSE.
A group that denies accepted climate science claimed that the actual CO₂ concentration in 2025 was 345ppm.
A gas like CO₂ is measured in parts per million (ppm), which expresses the concentration of substances in solutions like air, which is composed of multiple gases.
However, at no point in 2025 was atmospheric CO₂ at 345 ppm. Throughout the year, it steadily increased from 425ppm to around 430ppm at the end of the year.
The last time atmospheric CO₂ was close to the claimed amount was in the early 1980s. In the last 800,000 years, atmospheric CO₂ only rose above 300ppm from the 1960s onward.
This dramatic rise in atmospheric CO₂ is attributed to human activity, principally through burning fossil fuels. The increase in CO₂ and other greenhouse gases, such as methane, has raised the temperature to record levels.
Before 1958, CO₂ levels were estimated through ice core analysis. Mauna Loa Observatory in Hawaii hosts the world’s longest continuous CO₂ record. The Keeling Curve, revealing seasonal CO₂ variations, was first documented there.
PesaCheck has previously shown how the observatory, seen as the global standard, maintains the accuracy of its readings.
Mauna Loa's data is widely used in papers in prestigious journals and research institutions all over the world. Its data is also supported by findings of the United Nations International Panel on Climate Change (IPCC) and other measurements.
PesaCheck has examined a claim that atmospheric CO₂ stood at 345ppm in 2025 and finds it to be FALSE.
This post is part of an ongoing series of PesaCheck fact-checks examining content marked as potential misinformation on Facebook and other social media platforms.
By partnering with Facebook and similar social media platforms, third-party fact-checking organisations like PesaCheck are helping to sort fact from fiction. We do this by giving the public deeper insight and context to posts they see in their social media feeds.
Have you spotted what you think is fake or false information on Facebook? Here’s how you can report. And, here's more information on PesaCheck's methodology for fact-checking questionable content.
This fact-check was written by PesaCheck climate change fact-checker Christiaan van der Merwe and edited by PesaCheck chief copy editor Stephen Ndegwa.
The article was approved for publication by PesaCheck’s managing editor Doreen Wainainah.
PesaCheck is East Africa’s first public finance fact-checking initiative. It was co-founded by Catherine Gicheru and Justin Arenstein, and is being incubated by the continent's largest civic technology and data journalism accelerator: Code for Africa. It seeks to help the public separate fact from fiction in public pronouncements about the numbers that shape our world, with a special emphasis on pronouncements about public finances that shape government’s delivery of Sustainable Development Goals (SDG) public services, such as healthcare, rural development and access to water / sanitation. PesaCheck also tests the accuracy of media reportage. To find out more about the project, visit pesacheck.org.
PesaCheck is an initiative of Code for Africa, through its innovateAFRICA fund, with support from Deutsche Welle Akademie, in partnership with a coalition of local African media and other civic watchdog organisations.