New Zealand has told the international climate change talks in Mexico that unless changes are made to the rules on forestry, it can not commit to reducing emissions.
The Minister for Climate Change Issues, Nick Smith, revealed the Government's stance at the United Nations conference in Cancun.
The Green Party has labelled the move disturbing, while Labour says it is just an excuse for the Government having no plan.
New Zealand's commitment on climate change is to cut emissions at 1990 levels by 10 to 20% by 2020.
But Dr Smith says that will not stand unless New Zealand can get changes to rules on forestry in any future international agreement on emissions.
He says it must be recognised that not all the carbon from a tree is necessarily released when it is cut down, such as when it is made into building timber which is used instead of other high emission products.
"In fact, if the trees are produced into wood products that are used to replace concrete instead of buildings, there's a substantive ongoing climate change benefit of that carbon stored.
"We've made really good progress in these negotiations around not just recognition of domestic wood products, but also exported wood products that's quite important for New Zealand."
Dr Smith is also seeking changes to land use so there is no penalty for forestry land being converted to another use if forests are planted elsewhere.
He says the way carbon is measured at the time of harvest also needs to be changed.
Greens say emissions must be cut
Green Party co-leader Russel Norman says New Zealand needs to cut emissions, regardless of what the forestry rules are.
"The problem is, New Zealand now seems to be part of the problem in terms of being an obstacle to progress on either getting Kyoto part two, or another treaty that would result in real reductions in emissions."
Dr Norman says the Government's position will undermine the negotiations at Cancun. However, Dr Smith rejects that.
"New Zealand is playing a very constructive role in these negotiations. Our position is consistently around New Zealand doing its fair share on climate change.
"But we have no ambition to go out there and set some pegs in the ground of radical emissions reductions that would have a major cost on the New Zealand economy, that would make a negligible difference to overall global emissions unless it is going to be matched by substantive commitments from other developed countries."
Minister's ultimatum an excuse - Labour
Labour's spokesperson on climate change issues, Charles Chauvel, is also in Cancun and says Dr Smith's ultimatum to change the rules on forestry is just an excuse.
"And the reason that they can't commit to any proper emissions reductions target is that the watered down the ETS (Emissions Trading
System) and they've got rid of every other measure that the last government put in place to try to get emissions down. There's simply no plan."
Mr Chauvel says any force that New Zealand has had in the past by being a moral leader on climate change is rapidly evaporating.
The meeting in Cancun is due to wrap on Saturday. No agreements have yet been reached cutting emissions, funding for developing countries to deal with climate change, or how to reduce deforestation.