Posted on 14 September 2024 by John Mason, Guest Author

Skeptical Science is partnering with Gigafact to produce fact briefs — bite-sized fact checks of trending claims. This fact brief was written by Sue Bin Park from the Gigafact team in collaboration with John Mason. You can submit claims you think need checking via the tipline.

Does manmade CO2 have any detectable fingerprint?

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”.

Go to full rebuttal on Skeptical Science or to the fact brief on Gigafact

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?

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.