Wellington, Dec 18 NZPA - Green Party co-leader Jeanette Fitzsimons says New Zealand will face pressure to commit to a higher emissions reduction target if other countries do so.

Prime Minister John Key is attending a summit in Copenhagen ending a fortnight of talks seeking to reach agreement on a new United Nations pact aimed at averting dangerous climate change.

Today he delivered a speech calling for major economies to show leadership.

Green Party co-leader Jeanette Fitzsimons told Radio New Zealand that progress on the troubled talks now hinged on the United States.

She hoped President Barack Obama would be making an announcement about a higher target tonight NZ time or tomorrow.

The US has an emissions reduction target of 17 percent below 2005 levels over the next decade, equating to about 3 below the 1990 benchmark used by the UN.

Overnight US Secretary of State Hillary Clinton issued a pledge to help mobilise $US100 ($NZ136) billion a year by 2020 to assist poor nations.

Ms Fitzsimons said it was unlikely President Obama would leave the main announcement of the summit to Mrs Clinton.

"That suggests to me that Obama has something in his pocket, which to trump that, can only be a stronger target," she said on Radio New Zealand.

"If the US turns up, it could be tonight Copenhagen time or it could be tomorrow, and announces a more ambitious target for the US that will unblock a lot of the stand-off, it will allow China to move, it will allow the EU (European Union) to go to their 30 percent rather than 20 and suddenly things will look up.

"Let us hope that in that situation, despite what he said in the House last week, John Key will also step up and do a stronger target."

New Zealand's conditional target for reducing climate harming emissions is to reach 10-20 percent below 1990 levels by 2020.

"Any movement upwards will tend to lead to responses from other countries who will also move upwards. And maybe we get a deal that's not perfect but is still a deal that's worth doing," Ms Fitzsimons said.

A leaked report by UN climate scientists recommended cuts of 25-40 percent to give the world a 50 percent chance of staying below a 2 degrees Celsius temperature rise - considered a threshold of dangerous changes including more floods, droughts and rising seas.

Green Party co-leader Russel Norman said the report provided a strong argument for New Zealand to lift its target.

"The truth is, there is a lot that New Zealand can do to make substantial cuts to its carbon emissions at a reasonable cost. Making these changes now will help put our economy on a sustainable footing and will maintain our invaluable clean green reputation," he said.

Mr Key, in his speech, said New Zealand had come to the table with a "great hope" for a binding agreement to replace the Kyoto Protocol after 2012.

"It is sobering to have reached this point of the conference without having made progress on the major issues necessary for a comprehensive, effective and legally binding global climate change agreement."

He called on major economies to show leadership, saying New Zealand was acutely aware of the danger climate change posed for its Pacific island neighbours and big powers needed to consider the plight of vulnerable nations.

"Of all the options on the table at Copenhagen, failure is the one we can all least afford."

New Zealand was committed to playing its part, Mr Key said, citing its emissions trading scheme while also pushing New Zealand concerns around forests and agricultural emissions' rules and arguing against constraints on the carbon market.

"The wrong rules could significantly undermine New Zealand's future as a food producer to the world for no environmental gain."

Following the speech Mr Key told Radio New Zealand there was a lot of frustration at Copenhagen but with the leaders just arriving there was hope.

"We want to see some progress being made, I think in one sense maybe even if we start from a lower base just getting everyone on the same page and starting to move forward is potentially one of the most important things that we can do."

Ms Fitzsimons said it would not be a failure if the meeting adjourned so it could reconvene and get a better agreement.