The Copenhagen summit is unlikely to produce a "signed and sealed" climate change solution because leading countries are not ready to commit, the Environment Agency's chief will claim.

Lord Smith is calling for a reality check on the UN gathering, saying a treaty with "clear targets and measurable rapid reductions in emissions" is doubtful this year.

In his keynote address at the Environment Agency's annual conference in central London, he will say Copenhagen "won't solve all the issues - some of the most significant emissions countries aren't yet ready to conclude a deal, not least the US, where the Senate won't have made its decisions until the New Year."

Earlier this week Prime Minister Gordon Brown said that he was working hard to ensure a global deal on tackling carbon emissions at next month's environmental negotiations.

But Lord Smith says the summit must not be the last word in achieving a climate change solution but a "crucial start" for doing so.

He will add: "What we have to aim for, though, is a number of clear 'in principle' decisions, agreed by the participating nations, with a commitment to agree actions arising from those principles in the course of the following nine months.

"The commitment both to principles and to action must be genuine, and there must be a determination to move forward with urgency.

"Much of the focus of comment around the world has been on the development of 'cap and trade', to use economic incentives to change carbon-intensive behaviour. And I believe that cap and trade has to be a key part of the overall approach to reducing greenhouse-gas emissions.

"It's not a perfect mechanism, and it takes time to develop."

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