The Government has issued data confirming New Zealand is in credit under the Kyoto Protocol.
Satellite mapping shows that forests planted since 1990 are 18,000 hectares smaller than was earlier thought.
These are forests which can attract carbon credits and the Government says they are still big enough to offset a huge increase in greenhouse gas emissions since 1990.
Meanwhile debate is continuing on targets for emissions reductions by 2020.
An economic report for the Ministry for the Environment has costed a range of options.
Climate Change Minister Nick Smith says choices range from cutting emissions by 40% to raising them by 15%.
The Government will reveal its choice on 10 August and has hinted that a cut of 15% is the likely aim.
The Institute of Economic Research and Infometrics looked at four scenarios.
They calculated that a cut in emissions of 40% will cost around $3000 per person by 2020.
Based on estimated population growth by then, the study suggests this would amount to a cost of around $15 billion to the economy.
Another scenario, for a cut of 15%, would cost around $1400 per person.
A goal of 40% is urged by Greenpeace for adoption by New Zealand before a UN summit in Copenhagen in December on a successor to the 1997 Kyoto Protocol.