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UN Secretary-General Ban Ki-moon and Danish hosts have urged countries to compromise to salvage agreement on a new United Nations pact aimed at averting dangerous climate change as ministers struggled to break a deadlock in the talks.
"The next 48 hours is absolutely crucial," Dr Smith told Radio New Zealand.
"Ministers will be working, both (minister in charge of climate change negotiations) Tim Groser and myself, giving everything we can to try and make this conference successful.
"It really has been a long path from Bali two years ago to now where too many of the issues there's been little progress and that is why maximum effort has to be put in over the next two days."
Prime Minister John Key is attending the leaders' summit at the end of the week when he expects a high level agreement to be made with details to be worked out next year.
Talks were suspended for a few hours overnight New Zealand time over disputes about the level of emissions cuts by rich countries and a long-term global target to curb a rise in global temperatures which could trigger rising sea levels, floods and drought.
Draft texts dated Tuesday showed that national negotiators had stripped out figures for long-term global goals and rich nation emissions cuts by 2020 from last week's UN texts. The numbers could be re-inserted if agreement is reached.
New Zealand's conditional target for reducing climate harming emissions is to reach 10-20% below 1990 levels by 2020.
Dr Smith said the much higher 25-40% goal remained in play.
"There's pretty good agreement that that alone will not be enough and that one of the strong united positions of developed countries is that even if all of the developed countries sign up to that and you don't get those large growth emissions from developing countries under control this conference will not be a success and we cannot claim that we've got climate change under control," he said.
"What is encouraging for New Zealand is the level of unity amongst the developed countries ... yes they are prepared to make commitments but you've got to get the Chinas, the Indias, the Brazils also in the tent."
Dr Smith was encouraged by developed countries willingness to put money up to help developing countries adapt to climate change.