Power plant

To identify the cause of global warming, scientists study the carbon in our atmosphere.

Powell: “Carbon has three varieties: three different isotopes, all with the same number of protons, but three different numbers of neutrons.”

James Powell of the National Physical Sciences Consortium says these isotopes are found in different proportions in different substances. For example, the carbon found in plants has a distinct ratio of the isotopes carbon-12 and carbon-13.

There’s also a difference between the carbon isotopes in living plants and those in fossil fuels, which are made from plants that died millions of years ago.

That’s because plants contain the radioactive isotope carbon-14, which decays over time.

Powell: “Geological materials like coal, oil, and natural gas are so old that they no longer have any carbon-14.”

So by studying isotopes, scientists can measure exactly how much of the carbon in the atmosphere today came from fossil fuels.

Powell: “We can’t get away with saying that humans are not responsible for the carbon that’s been added to the atmosphere. The isotopes don’t lie and they show it.”

Reporting credit: Sarah Kennedy/ChavoBart Digital Media.

Samantha Harrington

Samantha Harrington, Associate Editor of Yale Climate Connections, is a journalist and graphic designer, with a background in digital media and entrepreneurship. "Sam" is especially interested in sharing...