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Researchers measure actual CO2 emissions from fossil fuel use and compare to reported levels

Researchers have measured CO2 emissions from fossil fuel use in California and compared them to reported emissions. This is the first time fossil fuel emissions have been independently checked for such a large area.

The team of researchers, led by researchers from Imperial College London (ICL), developed a technique to estimate CO2 emissions from fossil fuels using atmospheric measurements, then tested the technique over three months in California. An open-access paper on the work is published in Environmental Research Letters.

The study, funded by NASA, marks the first time scientists have been able to measure fossil fuel CO2 emissions over a large area such as California. The researchers suggest the technique could also be used in other regions, strengthening the ability to report and monitor efforts to curb emissions.

While there are many instruments that can measure CO2 concentration in the atmosphere, the difficulty is in separating natural CO2 from plant life from manmade CO2 emitted by fossil fuel burning. However, because gas, coal and oil are millions of years old, their carbon has a key difference compared to the carbon cycling through plants.

Fossil fuels lack a type of radioactive carbon, an isotope called carbon-14, which decays over time. By measuring the ratio of carbon isotopes in the samples the team collected, they were able to tell how much carbon was from fossil fuel combustion.

The team, which included researchers from ten different laboratories in the US, made their measurements at nine monitoring stations around California. They combined the data with a California-specific atmospheric circulation model, which shows how air moves around the state.

They then compared their results with other estimates of fossil fuel emissions, including estimates from the California Air Resources Board, who assisted with the study. The researchers found there was a good match between the different estimates.

We quantified ffCO2 by measuring radiocarbon (14C) in CO2, an accurate fossil-carbon tracer, at nine observation sites in California for three months in 2014-15. There is strong agreement between the measurements and ffCO2 simulated using a high-resolution atmospheric model and a spatiotemporally-resolved fossil fuel flux estimate. Inverse estimates of total in-state ffCO2 emissions are consistent with the California Air Resources Board's reported ffCO2 emissions, providing tentative validation of California's reported ffCO2 emissions in 2014-15. Continuing this prototype analysis system could provide critical independent evaluation of reported ffCO2 emissions and emissions reductions in California, and the system could be expanded to other, more data-poor regions.

—Graven et al.

California’s estimates are based on calculating what has been burnt and this study provided a way to check that their reported emissions are unlikely to have any large biases.

The researchers say that adding this atmospheric monitoring technique to the suite of tools used to monitor climate change can help to better understand greenhouse gas emissions from specific regions and how they are changing over time.


  • Heather D Graven, Marc L Fischer, Timothy Lueker, Seongeun Jeong, Thomas P Guilderson, Ralph Keeling, Ray P Bambha, Kieran Brophy, William Callahan, Xinguang Cui, Christian Frankenberg, Kevin R Gurney, Brian LaFranchi, Scott Lehman, Hope Michelsen, John B Miller, Sally Newman, William Paplawsky, Nicholas Parazoo, Chris Sloop and Stephen J Walker (2018) “Assessing fossil fuel CO2 emissions in California using atmospheric observations and models” Environmental Research Letters doi: 10.1088/1748-9326/aabd43


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