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Atmospheric chemistry shows that humans are driving the recent CO2 increase.
A key piece of evidence involves carbon isotope ratios in the atmosphere. Isotopes are different versions of the same element. Carbon comes in three isotopes of different weights and amounts: carbon-12 (98.9% of all carbon), carbon-13 (1.1%) and carbon-14 (trace amounts only).
Photosynthetic plants prefer the lightest isotope, carbon-12, because it is favored in photosynthesis reactions. That means plant tissues have relatively less carbon-13 than carbon-12. Fossil fuels, made of dead plants, also carry that distinct low carbon-13 isotope ratio, as does the CO2 produced by burning them.
Measurements over recent decades show a shift in the isotope ratio of atmospheric CO2, consistent with our burning of large amounts of ancient plant-derived carbon - in other words, fossil fuels. Natural carbon sources, like volcanoes, cannot explain this “fingerprint”.
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Sources
National Oceanic and Atmospheric Administration Stable Carbon and the Carbon Cycle
Global Biogeochemical Cycles Changes to Carbon Isotopes in Atmospheric CO2 Over the Industrial Era and Into the Future
National Oceanic and Atmospheric Administration How do we know the build-up of carbon dioxide in the atmosphere is caused by humans?
About fact briefs published on Gigafact
Fact briefs are short, credibly sourced summaries that offer “yes/no” answers in response to claims found online. They rely on publicly available, often primary source data and documents. Fact briefs are created by contributors to Gigafact — a nonprofit project looking to expand participation in fact-checking and protect the democratic process. See all of our published fact briefs here.
Posted by John Mason on Saturday, 14 September, 2024
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