The Government is sharpening its means of assessing how well New Zealand is complying with the Kyoto Protocol.
It says this could avert a potential loss to the Crown of $150 million per year.
New Zealand's greenhouse gas emissions have risen by almost a quarter since 1990 and the country has relied on growing forests to absorb carbon dioxide to offset this.
But the Ministry of Agriculture & Forestry says existing methods of assessing carbon storage are crude.
They look at species of tree, regions they are grown in and their age.
It now wants far more detailed analysis of each forest of more than 100 hectares, taking into account issues like soil quality.
The ministry says current methods risk over-estimating the amount of carbon growing forests actually absorb, potentially exposing the Crown to a liability between $60 - $150 million per year.