The Great Greenhouse Gas Grass Off

grass off hero

When New Zealand was first locked down because of COVID-19, an amazing opportunity also presented a dilemma. We wanted to see how far CO₂ emissions dropped under lockdown – but how?


Lockdown made it impossible for us to continue measuring greenhouse gasses in person. GNS Science radiocarbon scientist Jocelyn Turnbull asked people to cut weekly samples of grass near their homes. Grass grows quickly and would show changes in CO2 emissions as traffic and industry patterns changed because of lockdown.

The Great Greenhouse Gas Grass Off was created, complete with Facebook page. And the result? We gained some 300 citizen scientists who helped keep our CO2 measurement programme going during lockdown.

What did those tiny blades of grass show about CO2 emissions from traffic during lockdown? It dropped by as much as 80% in some cities.

The Project

Meet Jocelyn Turnbull

Jocelyn leads our radiocarbon and greenhouse gas research team. She studies the source and fate of greenhouse gas emissions in New Zealand and around the world. She works on projects in the USA, China, France and Australia. Jocelyn also studies how the Southern Ocean absorbs carbon dioxide. This results in her and others in the team sometimes taking hair-raising adventures to collect samples from places like Patagonia and Campbell Island.

X marks the spot

Jocelyn had some prime sites in mind: the inner city, near a park, shopping centre, motorway, busy road, or hills around a city. Why? Because they’re likely to show the largest changes in traffic emission levels, and because this where traffic is heaviest.

Our citizen scientists were asked to clip the same area every week for 10 weeks and then send in their samples. By 29 April 2020, Jocelyn had some 300 citizen scientists out snipping, bagging and storing grass.
On the Facebook page, 10-year-old Cameron Johns plotted the locations for us.
How we measured the CO2 in grass

What did we find from our 2020 grass clippings?

Sites in Wellington, Christchurch, Hamilton and Gisborne all showed a 75–80% drop in emissions during Level 4 compared to Level 1.

Suburban Auckland sites showed about a 70% drop, and Central Auckland sites showed an even smaller decrease in emissions – about a 40–60% drop. We expect that’s because buses continued running during Level 4.

There’s another measurement of what was happening during lockdown – a seismic noise. That’s the buzz of human activity on the ground, from traffic and construction to sports events. In the first Level lockdown in 2020, monitors showed seismic noise in Auckland was down to about 46% of normal. In the second level 4 lockdown, that noise was down to about 54% of normal.

The bigger picture

The Great Greenhouse Gas Grass Off did the job we needed. GNS Science is doing a similar job on a much bigger scale – measuring greenhouse gasses in urban areas. This project is ongoing with new measurements from the 2021 lockdown and application to longer term monitoring of NZ’s traffic emissions.

We’ve joined forces with NIWA, Manaaki Whenua Landcare Research, University of Waikato and Auckland Council on a New Zealand-wide greenhouse gas monitoring project called CarbonWatch NZ. This will give New Zealand one of the most comprehensive monitoring programmes in the world.

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Jocelyn Turnbull Radiocarbon Science Leader / Lead Scientist - Rafter Radiocarbon Laboratory

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Research Project Details


Funding Platform

GNS SSIF – Global Change Through Time, Ministry for the Environment (MfE)


Continues under lockdowns


Jocelyn Turnbull, GNS, Radiocarbon Science Leader / Lead Scientist - Rafter Radiocarbon Laboratory

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