A breakthrough at United Nations climate talks in Durban over the past two weeks still leaves many unanswered questions for long and arduous negotiations ahead, the Government says.

Deep in injury time, the Durban conference agreed to negotiate by 2015 a comprehensive agreement to come into force, if ratified, in 2020.

The nearly 200 countries represented seem to have got over a problem that has bedevilled international climate negotiations from the outset - the binary division of the world into developed and developing countries, with only the former expected to undertake binding commitments to curb emissions of greenhouse gases.

Although the "Durban platform" resorts to some elastic language on the the vexed issue of the legal form of the 2020 accord to come - "a protocol, a legal instrument or an agreed outcome with legal force" - it gave the European Union enough comfort to agree to sign up in the interim for a second commitment period of the Kyoto Protocol.

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Prime Minister John Key said yesterday that he thought New Zealand would also undertake commitments under Kyoto's second commitment period, now there will be one.

"But they are quite contingent on other countries and obligations they undertake," he said.

New Zealand has conditionally offered to cut its emissions to between 10 and 20 per cent below 1990 levels by 2020. The target for the first Kyoto period, which runs to the end of next year, is 100 per cent of 1990 levels.

Among the conditions are "comparable efforts by other countries" and "actions by advanced and major emitting developing countries fully commensurate with their respective capabilities". Others relate to rules about land use change and forestry - on which progress was made at Durban - and full recourse to a broad and efficient international carbon market.

Climate Change Negotiations Minister Tim Groser said the negotiations for the long-term regime beyond 2020 would be long and arduous.

And in a statement with Climate Change Minister Nick Smith he left open the possibility that New Zealand's commitments after 2012 might not be within the framework of the Kyoto Protocol but rather "join all the developing countries, the United States, Canada, Japan, Russia and others, in making those commitments under the alternative transitional arrangements described in different texts".

"It is not a matter of whether we make commitments - New Zealand will - but where they are made and how ambitious we should be," they said.

Simon Terry of the Sustainability Council said of the Durban meeting: "It saved the UN process. That's good. But the deal leaves shamefully inadequate emissions targets in place for a critical decade. It does not begin to address dangerous climate change in the sense that best case for the pledges outlined so far we are talking about [warming of] 3.5 degrees plus."

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Nigel Brunel of carbon brokers OMF Financial said nothing major was expected from Durban. "And we didn't really get anything major. But we have got a road map going forward. That's relatively positive."

It would have been a dampener on the carbon price if Durban had been a complete shambles and everyone had walked away, he said.

But he disputes the view that the recent collapse in the price of carbon was because of concerns there might not be a successor to Kyoto.

Even without that international regime, emissions trading schemes in Europe and New Zealand would continue and potentially be joined by Australia and regions within China and the United States.

Trading among that emerging archipelago of schemes was more important than the top-down Kyoto approach.

The main influence on the carbon price, Brunel believes, is the European recession.

"The carbon price has done exactly what it should have done when a lot of countries are in a lot of pain. You don't want a high carbon price when some companies are struggling to keep their doors open," Brunel said.

"If instead there was a tax in place, would Governments have reacted quickly enough to bring the tax down, as the market has?"