The Copenhagen summit is set to do "real business" because of President Barack Obama's decision to attend its crucial final stage, says Climate Change Minister Nick Smith.
Dr Smith said the summit was rapidly gaining momentum, with 105 world leaders now signed up for the final day.
The US President had originally planned to stop in on his way to a Nobel Peace Prize gathering in Norway this week, but announced at the weekend that he will now go for the world leaders' meeting on December 18.
This is the stage Prime Minister John Key will attend, and is when most of the final top-level negotiations on greenhouse gas reductions are expected to be be hammered out.
Indian PM Manmohan Singh yesterday said he would also attend the world leaders' meeting in what was deemed as another encouraging sign.
Dr Smith said Mr Obama's rethink was the leading factor in the increasing optimism for the summit, which begins today.
"That really says that we are starting to shake down and do some real business."
A spokesman for Mr Key said he welcomed Mr Obama's u-turn, adding if progress was to be made it required the attendance of the major emitters.
China, the US, Russia and India are the biggest emitters, in that order.
Mr Key decided only last week to attend Copenhagen, after earlier saying he would go only if a deal was close.
Dr Smith said the mantra of his negotiating team was "for New Zealand to do its fair share" to stop global warming. "Not more, not less, but our fair share towards a global solution."
He said recent efforts by climate-change sceptics to discredit the work of leading meteorologists ahead of the summit, including hacking computers, was "a bit of a sideshow".
The first week of the fortnight-long summit will mainly involve officials, before environment ministers like Dr Smith arrive next week.
Dr Smith said the growing numbers of world leaders signing up for the final stage meant there would be "enormous pressure" to deliver up a deal.
NZ's ambition was for the summit to yield a high-level political statement with a strong commitment to working through 2010 on the concrete details of an international treaty.
He said the impact on NZ depended on an inter-related set of outcomes from the summit: how much developed countries agreed to reduce emissions, how much money was committed to a global fund to help developing nations reduce emissions, and the extent to which these developing countries agreed to constrain their gas output.