Researchers say this mysterious – and huge – carbon sink could eventually count towards New Zealand’s climate goals, potentially slashing the multi-billion dollar price tag the government is facing to meet international obligations.

However more research is needed to include this sink in the national inventory, as well as to show it is due to human action so it could count towards the country’s reductions. But there is no guarantee the project will get more funding, despite its potential benefits.

According to the NIWA-led study, South Island forests, which had been considered roughly carbon neutral, could be absorbing 50-140 million more tonnes annually.

It’s a massive amount of carbon. For perspective, New Zealand’s total gross emissions in 2023 were 76.4 million tonnes, while the shortfall between our domestic emissions reductions and our Paris Agreement target for 2021-2030, which the government has promised to meet through buying offshore mitigation, is 84 million tonnes.

Study leader, NIWA atmospheric scientist Dr Beata Bukosa, says the study’s findings could have implications for New Zealand’s greenhouse gas reporting, carbon credit costs, and climate and land-use policies.

In the world-first research, scientists used advanced modelling and NIWA’s supercomputer to examine a decade of atmospheric data, from 2011 to 2020, to better estimate the amount of CO₂ absorbed by New Zealand's land ecosystems.

“Earlier estimates of how much carbon was removed by New Zealand land ecosystems ranged from a net 24 to 118 million tonnes a year,” says Bukosa. “Our research found that New Zealand’s natural environment absorbed approximately 171 million tonnes of CO₂ annually.” 

The NIWA team worked with collaborators at GNS Science and Manaaki Whenua as well as other New Zealand and overseas universities and institutes.

The team used an ‘inverse modelling’ technique, combining atmospheric greenhouse gases with a model showing how air is transported through the atmosphere to identify CO2 sources and sinks, and compared the results against New Zealand’s Greenhouse Gas Inventory as well as ‘bottom-up’ models. While the Inventory applies a combination of field inventory, modelling, and remote sensing to quantify forest carbon stocks and stock changes, the ‘bottom-up’ models use calculations based on ecosystem processes, land use and climate across the country.

Far-reaching implications

Bukosa says the largest differences between earlier estimates and the new findings came in the South Island. “This was especially in areas dominated by mature native forests and certain grazing lands.”

The research follows a pilot study in 2017, which also suggested indigenous forest in Fiordland might be absorbing more CO2 than expected. “That study was based on only three years of data, and we weren’t sure if it was just a transient effect related to the climatic conditions, or if the effect was confined to Fiordland. Our new study shows the carbon sink is more widespread than we thought, particularly across the South Island, with greater uptake of CO2 extending up the West Coast,” says Bukosa.

With improvements in modelling techniques and data coverage, the researchers have shown the extra carbon uptake has persisted for at least a decade. “More research could help us understand exactly why our method has shown such a difference in the carbon source and sink balance compared with other methods.”

Bukosa says the processes enabling the carbon sink could be unique to New Zealand's ecosystems. “If you think about New Zealand and the southwest coast, what's happening there can be different from other countries and forests. These are regions where we have quite a bit of precipitation. We have also quite a bit of landslide erosion.

“So, what might be happening, is that some of the carbon is being buried and then washed off to rivers and lakes and then exported potentially into the ocean, which from the atmospheric view will show up as a sink. Now, the question is, is this really a sink? Is the carbon coming back to the atmosphere? So, that's why we need to figure out what's happening.”

She says another explanation for the carbon sink could be forest regeneration due to different disturbances.

“It can be landslides, but also pest eradication or browser management. So there are a few projects happening - amazing projects across New Zealand – where they try to remove the pests from the forests, which means you get a better, stronger, healthier forest which has a stronger capacity to take up carbon. So these things can be specific to New Zealand.”

Further work needed

Dr Andrea Brandon, a Ministry for the Environment principal scientist who co-authored the study, said the findings help build a clearer picture of the role New Zealand’s natural systems play in absorbing emissions from the atmosphere. However, further work is needed before they can be included in official emissions reporting.

Troy Baisden, Motu affiliate, co-president of the New Zealand Association of Scientists and a co-author on the study, says the research represents a great opportunity for New Zealand to at least partially meet emission reductions targets without buying carbon mitigation from other countries.

“But surprising new science can also have trouble getting funded and demonstrating its results at the needed scale - there has in particular been a lot of pushback from the scientists involved in conventional measurements and locations.”

Researchers would need to demonstrate the carbon sequestration is due to human intervention for it to count towards climate targets, with several ways this could be happening.

“In addition to managed forests, the main options identified have to do with small changes to optimise the Manapouri power scheme, pest management in the conservation estate, and assisted regeneration after erosion, landslides, or disturbance,” Baisden says.

For about $10 million dollars more for the research, the project could potentially save the country billions in offshore mitigation.

Baisden notes New Zealand’s 84 million CO2e emissions reduction shortfall to the 2030 Paris target, which the government has promised to meet by financing climate action overseas. “That’s a gap of almost $5 billion NZD at current NZ ETS pricing, and is still worth nearly $1 billion when considering lower value nature-based avoidance units. If we don’t make some sense of one or the other, there’s a risk that Europeans might see it as a gap of over $12b if they use their current carbon pricing when considering border tariffs.”

Over-reliance on mitigation

While successive New Zealand governments have promised to meet the Paris Agreement nationally determined contribution (NDC) through buying international mitigation rather than cutting domestic emissions, the government is currently tying itself in knots saying it will honour that agreement while failing to take action to ink the bilateral deals necessary for offshore mitigation.

While Climate Change minister Simon Watts has said the cost of climate targets is “misinformation”, Prime Minister Christopher Luxon recently told an audience of farmers that quitting the global climate change agreement would affect trade.

The country’s over-reliance on offshore mitigation to meet nearly two-thirds of its total emissions cuts for 2021-2030 makes it a global outlier, which the government has been warned won’t go unnoticed by the international community, with the possibility of trade sanctions if targets are not met.

It might seem this research could be the get-out-of-jail-free answer to the government’s “least-cost” net emissions reductions prayers. The government could potentially have its climate cake and eat it too, doing very little to reduce gross emissions, while still legitimately claiming the unexpected reductions as long as they can be tied to additional human intervention.

However the government hasn’t said it will ensure funding for the project, which requires collaboration between multiple science organisations and was originally funded through the Endeavour fund.

Carbon News asked minister Simon Watts whether the government would look at ensuring funding for this research, given the potential benefits. However we did not receive a response ahead of press time.

Baisden says the project is an example where future (contestable) funding is an issue, with Endeavour cancelled for a year but perhaps more appropriate opportunities through institutional funding. However funding requires interactions across two PROs, universities and independent research organisations. 

“There is a lot of opportunity there. Why wouldn't we spend a few millions to catch the fish we deserve to get credit for?”

Continuing cuts to science funding are also eroding New Zealand’s ongoing potential to undertake important climate research.

“We’re in danger of losing the people who have specific skills in this area. Every loss is big to the science community at the moment.”

Baisden says it would have been better to have funded the project earlier and with more stability. “Because it has big payoffs for the country with lead times of at least 5 to 10 years. Of course, they say the best time to plant a tree was decades ago, but the second best time is now.

‘Wake-up call’ - Forest & Bird

Forest & Bird says the research should be the catalyst for urgent government action to knock down populations of pest deer, pigs, goats, wallabies, and possums that are wrecking native forest carbon sinks.

“This new research from NIWA proves that our native forests are working hard to draw down vast amounts of carbon from the atmosphere,” says Forest & Bird’s forests advocate, Dean Baigent-Mercer.  

“But our ngahere is achieving this with one hand tied behind its back. This incredible carbon capture – approximately 171 million tonnes of carbon dioxide annually between 2011 and 2020 – is happening despite the fact that many of our native forests are under constant attack by millions of pest deer, pigs, goats, wallabies, and possums.”

Baigent-Mercer notes that a report by Federated Farmers has already put the economic cost of pests at more than $200 million a year to our primary industries.  

“The NIWA-led study is a wake-up call and reinforces the urgent need for large-scale co-ordinated action to knock pest animals to low levels, and keep them down, so our native forests have the greatest opportunity to lock in even more carbon each year,” Baigent-Mercer says.

“This is the best spend for taxpayers’ money, not sending taxpayers cash overseas as our Nationally Determined Contribution on climate change to pay other countries to lock in carbon. We need to back our own native forests.

“We are currently in a devastating cycle of destruction where native forests are constantly being eaten from the top-down by possums and from the ground-up by deer, goats, wallabies, and pigs, year in year out, which really undermines how much carbon native forests can lock in.  

“These pests scoff the next generation of forest before it can grow, as well as killing mature trees. As trees die, they rot and release carbon dioxide, which feeds more climate change, which kills more trees that rot and release more carbon dioxide, fuelling more climate change.  

“These damaged native forests can’t hold land or water as well as they used to, so the risk of flooding downstream of homes, businesses, and towns increases. The only way to stop this cycle is to have co-ordinated long-term action across catchments with people resourced and working together to keep pest animal numbers as low as possible – allowing forests to recover to their full carbon capturing potential.

Baigent-Mercer says that protecting native forests is “one of the smartest investments” we can make. “It is a win-win-win by restoring our native biodiversity, preventing erosion and sedimentation in our waterways, as well as locking in carbon and connecting New Zealanders with nature.” 

Forest & Bird is calling on the government to: 

• Continue government investment in scientific research to improve how we measure carbon sequestration and emissions in native forests. 

• Fund and prioritise co-ordinated large-scale pest control on public and private land to protect these vital natural carbon sinks.

• Reset the governance of browsing pest animal control to enable effective action. 

• Creating incentives to better recognise and incentivise the carbon sequestration and biodiversity benefits of protecting and restoring native forests.

• Rejecting Herds of Special Interest (HOSI) proposals put forward by Minister of Hunting & Fishing James Meager to change the legal status of introduced pests by giving them ‘special protected status’ within national parks and other protected areas.