Former prime minister Helen Clark is optimistic climate change agreement can be reached at talks in December, after leaders gave positive speeches at the United Nations in New York today.

UN Secretary-General Ban Ki-Moon held a special event on climate change to try to muster political momentum before the December talks in Copenhagen.

Previously Miss Clark, in her role as head of the UN Development Programme (UNDP), had dampened down expectations.

Today she was far more positive.

"Actually I felt a little bit more optimistic about Copenhagen having heard some of the speeches today," she told media.

India and China had made positive moves and Japan today announced a 25 percent goal for reducing emissions by 2020 from 1990 levels, Miss Clark said.

The European Union remained committed, she said.

"From our point of view here this is a development issue. If this agreement comes off there's going to be a lot of money for development."

At Copenhagen more than 190 nations will try to agree a broader successor to the Kyoto Protocol, which obliged developed nations to cut greenhouse gas emissions, mainly from burning fossil fuels, until 2012.

Miss Clark said today's meeting was positive and United States President Barack Obama's speech and presence were important, even though he made no announcements.

"I felt the political ambience today was good, there were no bust ups at the interactive sessions with the leaders, yes people are waiting for the Americans to become more specific so I think they will go home with something to think about," she said.

"It's a question of timing now, there needs to be a lot of trying to bring people together before the Copenhagen conference."

Getting the leaders together was intended to inspire them to go home and tell negotiators to try harder "because it's important".

Earlier today Prime Minister John Key said the US and India were interested in backing a New Zealand initiative for a global approach to scientific research into reducing emissions from agriculture.

Mr Key said the US was open to financial backing.

He discussed the idea with Mr Ban during a 15-minute meeting.