Two fires that tore through sensitive peat wetlands in 2022 released more than half a million tonnes of carbon dioxide, pushing emissions from New Zealand's peat soils as a whole to a level comparable with BP or Mobil in this country.

Scientists have tallied the climate damage from fires at Kaimaumau and Awarua peatlands for the Department of Conservation, two years after fire-fighters struggled to contain the blazes using helicopters and ground crews.

The ecologically significant wetlands caught fire separately in 2022 - Awarua (in Southland) from suspected arson, and Kaimaumau (in Northland) when a legal fire to clear gorse to establish avocado orchards spread out of control.

The rare, intact peat wetlands are mainly on land managed by the Department of Conservation (DOC) and are home to rare native species.

They also hold deep stores of underground carbon built up over thousands of years.

A new report by Manaaki Whenua - Landcare Research for DOC said severe drought and drainage of nearby lands made natural wetlands much more flammable, and urged better care of New Zealand's remaining intact peat wetlands to prevent fires taking hold.

The carbon naturally stored in peatlands is not covered by New Zealand's Emissions Trading Scheme, but if it was, the report estimated the fires would have cost $32 million in carbon losses based on the current carbon price of about $50 a tonne.

Each fire also cost millions to extinguish, with the Kaimaumau fire forcing 30 families to be evacuated.

Manaaki Whenua said its best estimates of more than 515,000 tonnes of carbon dioxide emissions from Kaimaumau and more than 104,000 tonnes from Awarua were likely underestimates, and all of the carbon was released into the atmosphere.

In addition to those 2022 fires in intact peatlands, deliberate draining of peatlands that have been converted to farming - mainly dairying - produces an estimated 4.2 million tonnes of carbon dioxide a year.

Adding the impact of the 2022 fires pushes greenhouse gases from peat soil in that year to more than 4.8 million tonnes - above what oil company Mobil produced from all its New Zealand fuel sales in the year to June 2022 (4.7 million), and just shy of BP's tally of 4.9 million tonnes.

DOC freshwater scientist Hugh Robertson said calculating the carbon loss "really brings home the impact of wetland fires on New Zealand's stores of carbon".

He said peat soils were highly flammable, particularly when they were dried out.

He said reducing drainage and protecting wetlands was an important nature-based solution to climate changes, reducing emissions and making peatlands less likely to burn during future droughts.

Manaaki Whenua scientist Jack Pronger said the loss of carbon due to the two fires alone represented about 5 percent of New Zealand's total annual emissions target for 2026-2030.

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