In the middle of the once swamp-covered Hauraki Plains, surrounded by dairy farms, lies Kopuatai Bog, the largest remaining raised bog in New Zealand. Photo: RNZ / Alison Ballance
Analysis - An updated estimate shows just 1 percent of New Zealand's soil is releasing between 5 and 7 percent of the country's greenhouse gas emissions.
That is around twice what was previously calculated - and there is no plan in place yet to stop it.
A surprisingly high share of New Zealand's carbon dioxide emissions comes from a tiny proportion of soil - peat bogs that have been drained and are mainly used for dairying in Waikato, Southland, Northland and elsewhere.
Figures presented to Cabinet last year using improved, more accurate methods revealed peatland was producing an estimated 4 to 5 million tonnes of carbon dioxide a year, roughly double previous estimates.
Former climate change minister James Shaw presented the numbers to Cabinet as part of discussions on how to meet more of New Zealand's international climate obligations inside the country, enabling the government to buy fewer carbon offsets from overseas projects.
One of the domestic "opportunities" identified in the Cabinet paper was "reducing emissions from drained peatlands which currently contribute 4 - 5 (million tonnes) of CO2-e per year."
In July, the then-Labour Cabinet agreed in principle to progress work on widening New Zealand's international climate target to include reducing emissions from these soils (by 2030), possibly paving the way for farmers to earn carbon credits for tackling the problem.
The new climate change minister says he is still waiting for advice on the topic.
Goal should be to restore healthy wetlands - academic
New Zealand's official tally of greenhouse gases uses the old accounting methods for peat, which give a much lower estimate, however officials are gradually working towards adopting the improved methods that will give a more accurate - and damaging - picture.
Researchers have calculated this side effect of draining a small area of farmland could be responsible for almost 7 percent of the country's gross greenhouse gases, or 9 percent of net gases annually - more than all the coal and gas burned for generating electricity, or around a third to a half of what cars and trucks produce each year.
Waikato University Associate Professor Dave Campbell said the problem arose because the ancient, rainfed peat bogs, many metres deep, were releasing the carbon they built up over thousands of years, because oxygen-loving microbes could now get in and break down the carbon-rich deposits of vegetable matter.
Well, it was almost all vegetable - in Europe, he said, people occasionally found ancient bodies partially buried in the peat.
The carbon losses continue as long as the land remains drained, until the deep peat is entirely broken down and its carbon released to the atmosphere. That can take hundreds or thousands of years of ongoing emissions.
Campbell said early European settlers from the marshy Fenlands knew from experience how to drain peat to make land farmable, and set about digging drains, not realising the climate impacts. Fertiliser use, heavy machinery and trampling by animals have affected peat soil further, and its use for farming had intensified since the dairy boom, he said. Yet it can be productive farmland, which creates a conundrum.
"Most people don't realise that Hamilton is almost completely surrounded by peatlands. Early settlers started draining around the edges, and it's really only in the last few decades that his land has been used for dairy farming," Campbell said.
Campbell helped work on the more recent, improved estimates in a project for the Ministry for Primary Industries, and said current official estimates were "well out of date".
"On the one hand it's quite simple. The results of decades of international research shows the only surefire way to reduce these very large emissions from drained peatland soils is to rewet them."
Although only re-flooding the land can stop the carbon bleed completely, scientists are also testing to what extent raising the water table while keeping farming can reduce the losses.
Campbell said, ultimately, the goal should be to restore healthy wetlands, which could hopefully turn the peat back into a carbon dioxide sink.
But since peat soils' carbon dioxide emissions are not in the Emissions Trading Scheme (ETS), there is currently no financial incentive to do anything differently.
Peat soil emissions are not included in the roughly 50 percent of the country's emissions commonly attributed to agriculture, and it is not clear whether reducing emissions from peat soil will become part of meeting New Zealand's climate targets.
Govt still considering approach to peat emissions
Under the National Party's coalition deal with ACT, it agreed to look at widening the scope of activities farmers can earn credit for under the ETS.
Climate Change Minister Simon Watts said official advice on doing this, including whether peat soil might be part of the plan, had not yet been finished.
Most of the public debate on widening ETS categories has been around including smaller woodlots and native bush on farmland, to help offset greenhouse gases from sheep and cows.
But Campbell said you should not have one climate effect recognised, without the other.
He said giving out carbon credits for planting small woodlots, riparian vegetation or forests on drained peat soils, without counting the emissions of the peat underneath would be "kind of having your cake and eating it too". The overall effect could be worse for the climate than re-flooding the land.
With just 1 percent of land making as much as 9 percent of New Zealand's net emissions (meaning the tally including carbon sucked in by forests), he said it was a prime opportunity for action.
"If we could implement change land use activities or even look at retiring and restoring some of this land back to wetlands, it really is a low hanging fruit."
RNZ asked Simon Watts about the new government's approach to peat emissions.
He said the government was considering including wetlands and other sequestration categories in the Emissions Trading Scheme, possibly including re-wetting peat bogs.
Broadening the ETS to include more options for farmers was something the government had agreed to do, but Watts said official advice on what exact activities should be included was not ready.
"It is an area where we have said more broadly we are wanting to reinforce the good work farmers do... however we need to work through a process of how that will would work in practice," he said.
Federation Farmers and Dairy NZ declined to comment.