France clashed with other EU nations Thursday over how to calculate carbon emissions absorbed and emitted by forests, a key component of a climate deal being hammered out at UN talks in Copenhagen.

French climate ambassador Brice Lalonde slammed a proposal favoured by countries with huge forestry industries -- especially Finland, Sweden and Austria -- as containing "sloppy, even fraudulent" accounting methods.

Worldwide, deforestation and forest fires account for 12 to 20 percent of total greenhouse gas output, so being able to accurately measure changes in those emissions is critical in the overall effort to tame global warming.

How that is best done is what has divided the EU bloc of 27 nations.

France has taken the lead in calling for a totally transparent accounting practices, a position applauded by green groups.

But other countries, notably major consumers of wood as a heating fuel, have proposed to project generous envelopes of their forest-related emissions up to 2020, which they would then promise not to use up.