Efforts to forge a new global agreement on global warming will not repeat the mistakes that dogged the landmark climate summit in Copenhagen five years ago, Ban Ki-moon’s special envoy on climate change has vowed.



“This is a different environment to Copenhagen,” Mary Robinson, the former president of Ireland, told the Guardian. “Pressure on leaders for an agreement is building up more than 12 months ahead. I think leaders realise they need to have transformative change.”



More than 120 heads of state are meeting at a climate summit in New York on Tuesday, convened by the UN secretary-general in the hope that a series of personal meetings will allow them to break the stalemate that has marked climate negotiations for most of the last two decades.



It is the first time that world leaders will meet to discuss global warming since the Copenhagen summit. Although that occasion produced the first joint commitments on emissions by major developing as well as developed economies, it was marred by scenes of chaos and recriminations in the closing hours.



But Robinson, who served as UN high commissioner for human rights from 1997 to 2002, said that this time there should be a deal on the table in advance of governments meeting.



Though a comprehensive climate deal has often seemed elusive, Robinson insisted that the world’s governments would be capable of a solution. “We have done it before, on issues such as slavery. We need to move as rapidly as possible.”



She played down concerns that China and India had snubbed the secretary-general’s meeting, as neither Chinese president Xi Jinping and India’s prime minister Narendra Modi are planning to go. “China [is sending] a very, very senior participant,” she said.



She said she was hopeful of progress. “We need ten to 12 leaders to be ambitious...President Obama, I hope, will make a strong statement at the summit. ”



This week’s summit of leaders will be followed by a series of meetings by ministers and other officials culminating in a crunch conference in Paris next December. At that meeting, governments are supposed to forge a new global agreement on greenhouse gases for beyond 2020, when current emissions targets run out.



By the end of next March, said Robinson, all major economies, developed and developing, should have put forward their proposals on national emissions targets for beyond the end of the decade.



But key issues remain to be resolved, including whether future emissions should be divided up according to a “carbon budget”, based on scientific estimates of how much more carbon dioxide can be poured into the atmosphere without pushing the world over 2C of warming above pre-industrial levels. That symbolic threshold is regarded as the limit of safety, beyond which the effects of climate change - including droughts, floods and extreme weather - are likely to become severe and potentially irreversible.



There are still deep divisions over how far major developing countries should have to take a share of emissions cuts, and to what extent issues such as the historic responsibility for emissions, per capita emissions, and likely future economic circumstances should be taken into account.



The attempt to draw a distinction between the events of Copenhagen and the current negotiations reflects the high stakes involved.

Paris is widely seen as a last chance for the UN process, which has been running since 1992 but has suffered a series of highs and lows, including the 1997 Kyoto protocol which went unratified by the US, the drama of the Copenhagen summit, and long wrangling over seemingly intractable issues such as how to provide financial incentives for cuts in emissions and a price on carbon.



For some countries, the stakes are even higher.

Anote Tong, president of Kiribati, one of the Pacific Ocean’s small island nations, visited the Arctic ahead of this week’s meeting. He told the Guardian: “We are facing [climate change] now. I have seen how much ice is being lost and it is very serious. I will be bringing this message.”

