More than 120 leaders are to attend the summit on Tuesday called to inject new momentum in efforts to address climate change ahead of a crucial conference in Paris next year.

"The message from the climate summit and the message going forward to Paris is that it's not business as usual with a little bit of green attached," Robinson said.

"It's changing course. It's taking decisions that will bring us back to a trajectory that will give us a safe world that stays below 2 degrees Celsius. We are not on course for that. We need to change course," Robinson added.

United Nations is seeking to limit global warming to two degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial levels, but scientists say current emission trends could hike temperatures to more than twice that level by century's end.

US President Barack Obama is to outline his vision for reining in greenhouse gas emissions, but key polluters China and India are sending lower-level representatives.

Robinson dismissed suggestion that the absence of leaders from China and India, the world's number one and number three polluters, had dealt a blow to the summit's ambitions.

China is sending Vice Premier Zhang Gaoli while India's new much-awaited Prime Minister Narendra Modi is dispatching his environment minister.

"We will have the largest gathering of heads of state ever on the climate issue at a time when the world knows that we need to move urgently," said Robinson.

The former Irish president was appointed by UN Secretary General Ban Ki-moon in July to shepherd preparations for a summit seen as key to avoiding a repeat in Paris of the failure of the 2009 Copenhagen gathering.

The summit is being held on the eve of the high-level UN General Assembly meeting where world leaders will try to agree on a common approach to address the Islamist threat in Iraq and Syria, the Ebola crisis, the Israeli-Palestinian conflict among other issues.

"The climate summit hopefully will generate quite a bit of momentum and some surprises and a sense that we can actually get on top of this big issue," said Robinson.

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