The US delegation gave notice it would fight any EU attempts to bar GM trees from a Kyoto scheme to plant forests that will help offset global warming -- so-called "sinks" that soak up carbon dioxide (CO2), the principal gas blamed for climate change.

A draft version of the text to define how this scheme should be implemented said countries should evaluate "potential risks" arising from the use of genetically modified organisms (GMOs) and invasive species, "in accordance with their national laws."

"We felt particularly that this singling out of GMOs was inappropriate in this context," US chief climate negotiator Harlan Watson said.

"We did make our views to some of the Kyoto parties in the discussion," Watson said, without naming names.

As a result, the contested text was shifted to the preamble of the document, rather than its operative section, he said.

Even though this move makes the reference to GM trees non-binding, Washington insisted on putting its concerns on the record as "a miscellaneous document," he said.

"We do not consider that this sets a precedent whatsoever" on any bar on GM trees, he said.

The squabble touched on one of the most arcane, but also most politically explosive, areas of the Kyoto Protocol.

The UN's global warming pact -- still needing Russia's vote to make it take effect -- will allow industrial countries to plant "sinks" in developing countries to help offset their own CO2 pollution.

Even though the United States has walked away from the Protocol, it is still a full member of the parent accord, the United Nations Framework Convention on Climate Change (UNFCCC), and this gives it the right to observer status in Kyoto talks, although it cannot cast a vote.

"We continue to monitor a number of Kyoto discussions to make sure any decisions coming out of those discussions would (not) impact the US status, either as a party to the UN framework convention or set a precedence that could spill over into other international agreements," Watson said.

GM food technology has already driven a deep rift between the EU and United States.

The EU on Monday left intact a de-facto moratorium on importing and planting GM crops, a move that angered Washington, which has already filed suit at the World Trade Organisation (WTO) for what it brands green protectionism against US farmers.

European environmentalists defend the GM ban on the grounds of the "precautionary principle" -- the right of a country to block a new technology if it is potentially harmful for the environment or health.

The scientific consensus is that there is no evidence that the current generation of GM crops poses any such threat.

But many scientists also say too little time has elapsed to make a full safety assessment and that the impact of future, more ambitiously-modified plants is unclear.

There are no commercial species of GM trees yet, but that innovation may not be too far away if there is the incentive under Kyoto to plant fast-growing trees that swiftly soak up CO2.

The UNFCCC conference in Milan wraps up on Friday, after ministerial-level talks Wednesday and Thursday.

Kyoto requires industrialised signatories, but not developing ones, to meet pledged reductions in output of six greenhouses gases by a deadline of 2008-2012 compared with their 1990 levels.

Scientists say that "sinks" are at best only a temporary help for global warming unless they are managed carefully and the CO2 stored by the trees is not released.

The stored CO2 returns to the atmosphere after the tree dies and starts to rot.

SPACE.WIRE