Forest & Bird says burning coal from potential new mines on the Buller Plateau could put as much carbon dioxide into the atmosphere as another three million cars on New Zealand's roads for the next 20 years.
Earlier this month, 1 NEWS confirmed controversial Government proposals for open-cast mines on the massive plateau.
"These planned mines will be a disaster for the climate, as well as for the unique native species and habitats of the Buller plateau," Forest & Bird Climate Advocate Adelia Hallett said today.
The conservation organisation says it has calculated that over 20 years, up to 186 million tonnes of CO2 could be produced by burning coal from the new mines.
The coking coal is destined for steel manufacturing in developing countries, it said.
Over the same 20 year period, 1.4 million tonnes of 'fugitive emissions' - methane released as the coal seam is disturbed - would be released directly into the atmosphere as the coal is mined, Forest & Bird said.
"The Government will argue that this coal will be burnt in China or India, not here in New Zealand, and is therefore irrelevant to the climate change commitments they made in Paris," Ms Hallett said."
"Try and tell that to the climate. No matter where the coal is burnt, it's all taking us in the same direction - dangerous climate disruption."