Fact check: CO2 is 0.04% of Earth's atmosphere; do humans contribute only 3% of that to the atmosphere?

1. Summary of the results

The analyses confirm that CO2 constitutes approximately 0.04% of Earth's atmosphere ^{[1] [2]}. However, the sources do not directly support the claim that humans contribute only 3% of atmospheric CO2. Instead, the evidence points to a much more significant human impact on atmospheric CO2 levels.

Key findings from the analyses:

• Human activities have raised atmospheric CO2 by 50% since industrial times ^[3], with concentrations increasing from a pre-industrial baseline of 280 ppm to about 422 ppm in 2023 ^[2]
• The long-term trend of rising carbon dioxide levels is driven by human activities, specifically the burning of fossil fuels ^[4]
• Human and livestock respiration alone contributes 5-10% of fossil fuel emissions in most cities, reaching as high as 38.2% in cities like São Paulo ^[5]
• About 90% of respiratory carbon is released in urban areas ^[5]

2. Missing context/alternative viewpoints

The original question significantly understates the human contribution to atmospheric CO2. The analyses reveal several critical pieces of missing context:

• The question conflates total atmospheric CO2 with the human contribution to CO2 increases. While CO2 is indeed 0.04% of the atmosphere, this percentage has grown substantially due to human activities ^{[1] [2]}
• The 50% increase in atmospheric CO2 since pre-industrial times represents a massive change in Earth's atmospheric composition ^[3], far exceeding the implied 3% human contribution
• The question ignores the cumulative effect of human emissions over time. The analyses show that human activities are the primary driver of the long-term upward trend in CO2 concentrations ^[4]

Industries that benefit from minimizing perceived human impact on CO2 levels include fossil fuel companies, which have historically funded research and campaigns to downplay human contributions to climate change. Climate scientists and environmental organizations benefit from emphasizing the significant human impact on atmospheric CO2 concentrations.

3. Potential misinformation/bias in the original statement

The original statement contains misleading framing that significantly understates human impact on atmospheric CO2:

• The 3% figure appears to be unsupported by the scientific evidence presented in the analyses, which instead demonstrate substantial human influence on atmospheric CO2 levels
• The question uses a rhetorical structure ("do humans contribute only 3%") that suggests human impact is minimal, contradicting the scientific consensus reflected in the sources
• The framing ignores the dramatic increase in atmospheric CO2 concentrations since pre-industrial times ^{[1] [2]}, which the analyses attribute primarily to human activities
• The statement fails to acknowledge that even small percentage changes in atmospheric composition can have profound climate effects ^[6]

This type of framing is commonly used to minimize public concern about human-caused climate change and has been historically promoted by organizations with financial interests in continued fossil fuel use.