Published: June 2, 2020 By
Preparing NOAA air samples

CU Boulder researcher Chad Wolak prepares NOAA air samples for carbon-14 measurement. (Credit: Scott Lehman)

Researchers from NOAA and CU Boulder have devised a breakthrough method for determining emissions of carbon dioxide from fossil fuel combustion, which will also lead to more accurate estimates of carbon exchange between the land and atmosphere.

In a paper published June 1 in the Proceedings of the National Academy of Sciences, the researchers report the first-ever national estimate of fossil-fuel derived carbon dioxide emissions obtained by observing carbon dioxide and its naturally occurring radioisotope, carbon-14, from air samples collected by the NOAA Global Greenhouse Gas Reference Network.

This new method is also expected to provide a more accurate look at changes in fossil fuel emissions as the economy begins its recovery amid the COVID-19 pandemic. In addition, the method will be particularly robust at identifying year-to-year emissions trends, allowing governments to independently assess their progress toward meeting the Paris Climate Agreement goals. 

“Carbon-14 allows us to pull back the veil and isolate carbon dioxide emitted from fossil fuel combustion,” said Scott Lehman, a senior fellow at the Institute of Alpine and Arctic Research (INSTAAR) at CU Boulder and one of the paper’s authors. “It provides us with a clear fossil carbon dioxide signal we can track to sources on the ground. We can then add these up and compare to other emissions estimates at various time and space scales.” 

Carbon-14, also known as radiocarbon, is a well-known isotope that carbon scientists have relied on for decades to date archaeological sites. It’s a rare isotope of carbon created largely by cosmic rays, with a half-life of 5,700 years. The carbon in fossil fuels has been buried for millions of years, so the fossil fuel carbon humans burn and emit into the atmosphere is completely devoid of carbon-14.

With careful laboratory analysis the amount of carbon-14 in individual air samples can be measured, differentiating the amount of carbon dioxide coming from fossil fuel combustion and cement manufacturing from that removed or added by living plants, soils, etc. 

Map of emissions

The team used measurements of atmospheric carbon dioxide and its carbon-14 content to “unmask” the contribution of carbon dioxide from fossil fuel combustion and cement production. Because fossil fuels and materials used to produce cement are devoid of carbon-14, their emissions appear as areas of low carbon-14 (shown in warm colors) that can be traced back to sources at the surface using atmospheric transport models. (Credit: Sourish Basu)

“This is a new, independent, and objective method for evaluating emission inventories that is based on what we actually observe in the atmosphere,” said lead author Sourish Basu, who was a CIRES scientist working at NOAA during the study. He is now a scientist at NASA’s Goddard Space Flight Center in Maryland.

While the link between fossil carbon dioxide emissions and atmospheric carbon-14 has been known for many decades, the development of a national-scale emission estimate based on atmospheric carbon-14 required the simultaneous development of precise measurement techniques and an emissions estimation framework, largely spearheaded over the past 15 years by Lehman and NOAA scientist John Miller.

As these were the first estimates constructed using the new observing system, the scientists cautioned that they should be considered provisional. Now, they are busy applying the method to measurements from subsequent years to determine if the differences they see are robust over time.

Read more about this new study on the INSTAAR website.

This study was supported by NOAA, NASA, and the Department of Energy. Other members of the research team included scientists from Northern Arizona University and the University of California at Irvine.