The Green Party has released its own study claiming it is possible to dramatically and cheaply reduce greenhouse gas emissions to below levels set in 1990.
The study says reforms in the forestry, transport, energy and agricultural sectors could reduce emissions and achieve a target that is up to 40% below 1990 levels.
The reforms include closing Huntly's coal burning power station, cutting the size of dairy herds, planting more forests and ramping up pest control.
Green Party MP Jeanette Fitzsimons says while none of the initiatives are expensive she cannot put a figure on it.
However the Government says the Greens need to be up front about the impact a 40% emissions reduction would have on power prices, petrol prices and jobs.
Climate Change Minister Nick Smith says the Greens are grossly underestimating the cost of reducing emissions.
Next week, government officials will attend one of a series of international conferences to try and agree on a future target for reducing emissions.