Dramatic lockdown fossil fuel carbon dioxide decrease detected by citizen science supported radiocarbon observations

Jocelyn C. Turnbull1,2,*, Lucas Gatti Domingues1, Nikita Turton1

1Rafter Radiocarbon Laboratory, GNS Science, Lower Hutt, New Zealand, 2CIRES, University of Colorado at Boulder, CO, USA

The travel and work restrictions imposed by COVID-19 lockdowns resulted in dramatic changes in fossil fuel CO2 emissions around the world, most prominently in the transportation sector. Yet to date, most estimates of the change in emissions have relied on proxy data, and it is difficult to evaluate emission changes from CO2 measurements alone. Radiocarbon measurements are the gold standard for quantifying recently added fossil fuel CO2 into the local atmosphere, since fossil fuels are devoid of radiocarbon.

We used a novel citizen science campaign to collect grass samples from around New Zealand during the 2020 and 2021 COVID-19 lockdowns, when the highly restrictive lockdowns meant that scientists could not travel to collect samples in a more traditional way. We present the methodology of measuring radiocarbon content of the grass samples and calculating the recently added, local, fossil fuel CO2 mole fraction at the local and time period that the grass grew. We demonstrate that although there are some limitations and caveats of this method, it is possible to control for meteorological and other factors, and infer local fossil fuel CO2 emission changes from the grass data.

Our results from 17 sites in five cities around New Zealand demonstrate dramatic reductions in traffic emissions of 75 ± 3 % during the most severe lockdown restriction period. This is consistent with sparse local traffic count information, and a much larger decrease in local traffic emissions than reported in global aggregate estimates of COVID-19 emission changes. Our results demonstrate that despite nationally consistent rules on travel during lockdown, emission reductions varied by location, with inner city sites dominated by bus traffic showing smaller decreases in emissions than sites dominated by passenger vehicle traffic.


Jocelyn Turnbull holds joint appointments at GNS Science, New Zealand the University of Colorado, USA. Dr Turnbull started her career as a radiocarbon technician and lab manager, and then obtained her PhD on Development and Environmental Applications of Atmospheric 14CO2 Measurement from the University of Colorado at Boulder in 2006. She spent time establishing a global radiocarbon modelling capability at the Laboratoire des Sciences du Climat et de l’Environnement, before moving to the NOAA Global Monitoring Laboratory in Boulder, USA, where she was primarily involved in establishing urban greenhouse gas observational methodologies. In 2011, she returned home to New Zealand where she leads the GNS Science Rafter Radiocarbon Laboratory, which maintains expertise in a wide range of radiocarbon applications, supporting earth science research in New Zealand and around the world. Jocelyn’s research investigates the modern carbon cycle, particularly the source and fate of fossil fuel derived CO2, She uses radiocarbon and related tracers to understand the sources and sinks of greenhouse gases at the local, urban and regional scales. Current projects include: CarbonWatch-NZ evaluating New Zealand’s natural and anthropogenic carbon budget; INFLUX, the Indianapolis Flux Project evaluating urban greenhouse gas emissions; and SOAR, Southern Ocean Atmospheric Radiocarbon, investigating Southern Ocean carbon exchange. She is co-chair of the World Meteorological Organisation’s IG3IS initiative, connecting atmospheric greenhouse gas observations to local, national and international climate policy.

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Nov 17 2021


8:00 am - 8:45 am