Fact check: What is the current concentration (by volume) of carbon dioxide in the atmosphere? [Give as a percentage of the whole]

1. Summary of the results

The current concentration of carbon dioxide in the atmosphere is a crucial metric for understanding climate change. According to the analysis by ^[1], the latest measurement of carbon dioxide as of July 2025 is 428 ppm, which translates to approximately 0.0428% by volume of the whole atmosphere ^[1]. Similarly, ^[2] provides the monthly average carbon dioxide concentration at Mauna Loa Observatory, Hawaii, with the latest measurement being 425.48 ppm in August 2025, suggesting a concentration of approximately 0.0425% by volume ^[2]. In contrast, ^[3] mentions that the global average atmospheric carbon dioxide was 422.8 parts per million (ppm) in 2024, but does not provide the current concentration as of September 2025 ^[3].

• The range of concentrations reported by different sources is between 422.8 ppm and 428 ppm.
• The percentage of carbon dioxide by volume in the atmosphere is estimated to be between 0.0425% and 0.0428%.
• The highest monthly value each year occurs in May, with carbon dioxide hitting just under 427 ppm in May 2024 ^[3].

2. Missing context/alternative viewpoints

Some sources, such as ^[3] and ^[1], provide information on the composition of the atmosphere, including the percentages of nitrogen, oxygen, and argon, but do not calculate the percentage of carbon dioxide by volume ^{[3] [1]}. ^[4] discusses the increasing levels of carbon dioxide in the atmosphere but does not provide the current concentration or percentage of the whole ^[4].

• The total volume of the atmosphere is approximately 78.08% nitrogen, 20.95% oxygen, and 0.93% argon, with the remaining 0.04% consisting of other gases, including carbon dioxide ^{[3] [1]}.
• The rate of increase of carbon dioxide has accelerated since measurements began at Mauna Loa Observatory in 1958, with the anthropogenic component of atmospheric carbon dioxide increasing exponentially with a doubling time of about 30 years since the beginning of the industrial revolution ^[4].

3. Potential misinformation/bias in the original statement

The original statement asks for the current concentration of carbon dioxide in the atmosphere as a percentage of the whole, but does not provide any context or information about the sources or methods used to determine this concentration ^{[3] [1] [2]}.

• ^[1] and ^[2] provide more recent and specific data on carbon dioxide concentrations, which may be more reliable for determining the current concentration ^{[1] [2]}.
• ^[3] and ^[1] provide information on the composition of the atmosphere, but do not calculate the percentage of carbon dioxide by volume, which may be a limitation of these sources ^{[3] [1]}.
• The sources that benefit from this framing are those that provide more recent and specific data on carbon dioxide concentrations, such as ^[1] and ^[2], as they are more likely to be cited and relied upon for determining the current concentration of carbon dioxide in the atmosphere ^{[1] [2]}.