Image caption At climate talks in Durban in 2011, Mr Stern denied that the US is stalling action on climate change

The EU and small island states have criticised the US for saying the target of keeping global warming below 2C should be removed from climate talks.

At the 2010 UN climate convention meeting, governments agreed to take "urgent action" to meet the target.

But last week the chief US climate negotiator Todd Stern said insisting on the target would lead to "deadlock".

Spokesmen for the EU and the Alliance of Small Island States (Aosis) said the US should stick to promises made.

"Suddenly abandoning our agreement to keep global warming below 2C is to give up the fight against climate change before it even begins," said Tony de Brum, Minister in Assistance for the Marshall Islands.

"'Flexibility' on our 2C limit would set the world on a path to irreversible, runaway climate change.

"For many low-lying island states, including my own, that is not a solution - it is a death sentence," he told BBC News.

Isaac Valero-Ladron, the EU's climate spokesman, said governments including the US had to live up to prior promises.

"Also, consolidated science continues to remind us of the dire consequences of going beyond such a temperature increase," he said.

The core objective of the UN climate convention (UNFCCC), agreed in 1992, is to prevent "dangerous" climate change.

Scores of governments believe that 2C is a realistic indication of where "dangerous" climate change begins, although a greater number - principally those highly vulnerable to impacts such as sea level rise - say even 2C is too high.

Home front

Mr Stern's speech at Dartmouth College last Thursday was barely reported, but clearly expounded the Obama administration's thinking on climate change issues both international and domestic.

Lamenting the decline in media coverage in the US, he suggested that many regarded it as an issue too hot for them to touch.

"Climate change has long been a partisan issue, but when you see a parade of conservative candidates publicly recanting the apostasy of having acknowledged that global warming is real, you know you've entered Wonderland," he said.

Climate change glossary Select a term to learn more: Adaptation Adaptation Action that helps cope with the effects of climate change - for example construction of barriers to protect against rising sea levels, or conversion to crops capable of surviving high temperatures and drought.

"This is not healthy. We can talk past each other, close our ears, put our heads in the sand, or join the local chapter of the Flat Earth Society, but here's the thing - the atmosphere doesn't care.

"Its temperature will continue its implacable rise, with all the consequences that entails, unless we act to stop it."

It is precisely because of such concerns that the international community established the UNFCCC 20 years ago, and that many governments now want tougher action to constrain carbon emissions.

At the UN climate meeting last year in South Africa, governments agreed to launch a new process (the Durban Platform) that will agree a new deal including every country by 2015, to come into effect by 2020.

While it made sense on paper for those negotiations to aim for a collective emissions cap that would "guarantee" staying below 2C, Mr Stern said, it would not work politically.

"Insisting on a structure that would guarantee such a goal will only lead to deadlock.

"It is more important to start now with a regime that can get us going in the right direction and that is built in a way maximally conducive to raising ambition, spurring innovation, and building political will."

Although governments of many high-emitting countries might favour such a "bottom-up" approach, it is unclear how the US expects the approach to lead to emission cuts of a scale able to meet the ultimate objective of the UN convention - preventing "dangerous" climate change.

It is also unclear whether the US has the support of other governments.

A chief Chinese negotiator to the UNFCCC did not respond to a request for comment.

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