Efforts to secure a new global deal to tackle climate change hang in the balance, with a "real danger" they could fail, Foreign Secretary David Miliband warned today.

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With less than 100 days until talks in Copenhagen aimed at securing agreement on worldwide cuts in greenhouse gas emissions, UK ministers are worried the negotiations will not succeed.

The Foreign Secretary said the complexity of the issue, other problems such as the recession clouding the political agenda and "suspicion" between rich and poor countries were hampering progress.

But ahead of visits that will take him around Europe in a diplomatic push to raise the issue of climate change, he said a failure to cut emissions could lead to global temperature rises of 4C.

This would lead to large scale migration as parts of the world disappeared under rising seas, threaten infrastructure as extreme weather events became more common, and put pressure on natural resources such as water - all of which could have serious impacts on peace and security across the world.

"The deal the world needs in Copenhagen is now in the balance," he said.

"There's a real danger the talks scheduled for December will not reach a positive outcome, and an equal danger in the run-up to Copenhagen that people don't wake up to the danger of failure until it's too late."

The Foreign Secretary and his brother Climate Change Secretary Ed Miliband welcomed the announcement by the incoming Japanese government that it would cut the country's emissions by 25% on 1990 levels by 2020.

The Climate Change Secretary said that while the talks hung in the balance, the announcement by the Japanese government showed that "the jigsaw pieces are in place for a deal" and political will was required to tip the balance in favouring of securing a deal.