Papua New Guinea is among developing countries that may oppose proposed new rules for the way nations including New Zealand count carbon dioxide stored in vegetation such as trees as part of their emissions targets.
Industrialised countries may overstate projected carbon emissions from logging and land use and then take credit when greenhouse-gas output falls short, Kevin Conrad, Papua New Guinea's lead climate negotiator, told the Bloomberg news agency.
Climate talks began in Bonn, Germany, this week to reach agreement on land-use changes and forests in industrialised countries, the first major stop for global warming delegates on the road to the Cancun summit, the next UN climate conference in December.
John Ashe, chair of the climate negotiations under the Kyoto Protocol track, told countries they have until June 11, the last day of Bonn, to finalise the forestry and land use portion of the negotiating text.
The emissions accounting loophole was part of a new set of forestry rules added last year to the negotiating text under the Kyoto Protocol track of negotiations.
The 1997 Kyoto treaty requires participating wealthy states to cut their greenhouse gas pollution, but on a voluntary basis, as does the forestry section of the agreement, known as "Land Use, Land Use Change, and Forestry", or LULUCF.
The new rules would make accounting of forest emissions legally binding after 2012, when the Kyoto treaty's first commitment period ended, and would establish a baseline year for cutting emissions from forestry in the future, not in the past.
That could allow foresters to boost carbon emissions for several years, then measure compliance against this elevated future level.
A significant part of the New Zealand Government's strategy for lowering net greenhouse gas emissions involves using forests as a "carbon sink", with some foresters credited when they maintain canopy forest.
But some critics are concerned about the potential for countries to claim they are tackling climate change, but only make limited cuts in the use of fossil fuels, such as coal, oil and natural gas, said Paul Winn, a forestry adviser at Greenpeace who's following the talks.
Reuters reported one specific gap to be addressed in Bonn was whether developed countries should be allowed to exclude carbon emissions from cutting down trees to produce renewable energy.
Mr Conrad called that "fraudulent accounting" and the co-head of the EU delegation, Artur Runge-Metzger, told Reuters that such loopholes must be closed, under "harmonised" reporting rules.
The UN talks involving negotiators from 185 countries require consensus before proposals are accepted in any possible global deal.
Under the forestry and land-use proposal, industrialised nations could be effectively be credited with about 400 megatons of carbon dioxide they wouldn't have cut from fossil fuel consumption, worth €6 billion ($NZ10.8 billion) based on today's price for EU allowances for December delivery of about €15 a tonne.
US forests absorb the equivalent of about 10 percent of the country's entire output from the use of fuels such as coal. Most of Australia's planned emissions reductions could be accounted for by including the proposal, Mr Winn said.
"These countries are not willing to account for their actual emissions that the atmosphere sees," he said.
Canada, Australia and other nations want CO2 emissions due to natural disasters such as fires or beetle infestations not be counted.