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FACT BRIEF

Does manmade CO2 have any detectable fingerprint?

By Sue Bin Park
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YES

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”.

See a full discussion of this at Skeptical Science
This fact brief is responsive to conversations such as this one.
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?
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Skeptical Science
Skeptical Science is a non-profit science education organization. Our goal is to remove a roadblock to climate action by building public resilience against climate misinformation. We achieve this by publishing debunking of climate myths as well as providing resources for educators, communicators, scientists, and the general public. Skeptical Science was founded and is led by John Cook, a Senior Research Fellow with the Melbourne Centre for Behaviour Change at the University of Melbourne.
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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 fact briefs here.