World first: Scientists to map carbon profile of every NZ city and town

Cities remain New Zealand’s biggest source of carbon dioxide, but just how much CO2 they send into the atmosphere - or absorb with trees and parks - hasn’t been completely clear. Photo / Dean Purcell

Scientists have begun mapping our urban carbon footprint in a multi-million-dollar project to make New Zealand the first country with real-time emissions data for every town and city.

While our cities remain New Zealand’s biggest source of carbon dioxide, and many have set bold targets to cut their pollution, just how much CO2 they send into the atmosphere - or absorb with trees and parks - hasn’t been completely clear.

In Auckland, at least, scientists have been building a detailed picture of the city’s carbon balance - right down to areas as small as 500 square metres - through the collaborative research programme CarbonWatch NZ.

As with other cities, the vast bulk of Auckland’s greenhouse gas pollution came through carbon dioxide, with transport - accounting for roughly half of the region’s gross emissions - a major CO2 contributor.

For Dr Jocelyn Turnbull, who leads GNS Science’s radiocarbon and greenhouse gas research team, understanding how much CO2 urban landscapes drew down was comparably important as measuring what they produced.

“It’s well-known globally that urban trees and green spaces play an important role in managing temperature and cleaning the air, but the role of urban landscapes in offsetting emissions is very poorly known internationally - and not at all for subtropical cities like Auckland,” she said.

“Our research shows that the urban landscape may be a significant carbon sink, offsetting 10 per cent or more of Auckland’s emissions.”

In the new project awarded a $10.5 million grant through the Ministry of Business, Innovation and Employment’s (MBIE) Endeavour Fund, Turnbull and colleagues aim to expand on the success of the Auckland study to collect carbon balance information for all towns and cities - and to tease out the impacts of different urban development styles on fossil fuel emissions.

“Traffic emissions vary with [the] time of day, and day of the week, but we also know that how we build our cities can make a big difference to traffic emissions,” Turnbull said.

“One of the goals of this new research is to see how new developments - whether greenfields or urban infill - change traffic emissions.”

It will also look closer at emissions from industry - by far the biggest source of this in Auckland remained the Glenbrook Steel Mill - along with those from offices, commercial buildings and homes.

The Glenbrook Steel Mill, south of Auckland. Photo / Alex Burton

“In New Zealand, many people heat their homes with wood, but we really don’t know those emissions well at all,” she said.

“Wood-burning is good from a climate perspective, because it is renewable, but it does create a lot of pollutants, and we need to think more about the trade-offs of using wood for heating.”

There was also much more to learn about our urban carbon sinks.

“While our initial results suggest that the landscape is offsetting some of our emissions, we have a lot of new science to do to understand what is driving that,” she said.

“We’re adding new measurements in Auckland, Christchurch and other centres around the country that will help us determine the balance of carbon uptake by photosynthesis and carbon release by respiration.

“With further modelling, we will attempt to understand which types of urban environment are the biggest sinks, and how we might enhance them.”

Another “vital but unanswered question”, she said, was how new development changed urban landscape carbon uptake.

“Development choices will influence traffic emissions, and importantly, but less obviously, development also changes how much carbon is taken up by urban trees and parklands.”

Though there’s been a groundswell of efforts by cities to combat the climate crisis - C40 being the best-known - Turnbull said actually measuring and modelling urban emissions was still a relatively new area of research.

She happened to be part of the world’s first substantial project, which began in the US city of Indianapolis in 2010, and also collaborated with global counterparts around how to measure the dramatic emissions drops that came with Covid-19 lockdowns.

The data her team gathered, she said, would ultimately help analysts delve into how different socio-economic drivers influenced patterns - or what certain development scenarios meant for net emissions.

“With this detailed, validated emissions information in hand, Aotearoa can make informed urban planning and development decisions to mitigate emissions, now and in the future,” she said.

“How we manage our city parks, our front gardens and roadside verges can all make a really big difference to a city’s carbon balance - this research will help us understand how those green space management decisions result in an uptake or a release.”

The project is led by GNS Science, with research partners the National Institute of Water and Atmospheric Research (Niwa), Manaaki Whenua Landcare Research, the University of Auckland, DotLovesData, the Ministry for the Environment and Stats NZ.

GNS is also working with international collaborators from Australia, the US and Switzerland, and a stakeholder advisory group from central government, local government, iwi and industry.

Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.