Two environmentalist organisations say the expansion of New Caledonia's nickel sector will make the territory one of the worst per capita polluters.
The World Wildlife Fund and Conservation International have written to the territory's president, saying the annual per capita CO2 emission of 13.7 tonnes is set to rise to 36.8 tonnes.
The expected pollution increase is linked to the planned opening of two large nickel plants, which will be powered by coal-burning electricity sources.
The existing SLN nickel plant in Noumea is known for its large emissions but is due for an upgrade.
The two environmentalist organisations say efforts should be made to curb emissions.
They say the current plans will place New Caledonia into the top polluter group that includes the United Arab Emirates, Qatar and Kuwait.