UN Secretary-General Ban Ki-moon Monday underscored the urgent need for collective action to save the planet on the eve of the largest-ever gathering of world leaders on the issue of climate change. Kicking off the first-ever "Climate Week NYC" at New York City Library, Ban called on civil society, faith groups, businesses and governments to join forces to combat climate change.

"Your collective efforts are vital for generating greater public awareness on climate change," he said at the event also attended by former British Prime Minister Tony Blair.

United Nations Secretary-General Ban Ki-moon speaks during the opening ceremony of Climate Week NYC Monday, Sept. 21, 2009 in New York. [Xinhua/AFP]

Tuesday's summit, which is expected to be attended by some 100 heads of state and government, seeks to mobilize political momentum to "accelerate the pace of negotiations and help strengthen the ambition of what is on offer," Ban said.

United States President Barack Obama and Chinese President Hu Jintao are among the world leaders who will address the opening session of the gathering on Tuesday.

It will also feature a UN Leadership Forum Luncheon hosted by former US Vice-President and Nobel Peace Prize laureate Al Gore, which will mark the first time that global political leaders, as well as top business and civil society officials, will meet on such a large scale at the United Nations Headquarters in New York.

While not a negotiating session, the summit will allow world leaders to engage in direct discussions in small roundtable discussions, each co-chaired by a leader from a developing and developed country.

Ban also reiterated his call for governments to "seal the deal" on an ambitious new agreement to curb greenhouse gas emissions this December in Copenhagen, Denmark.

The deal to be reached in the Danish capital later this year would go into effect when the first commitment period of the Kyoto Protocol ends in 2012.

"A climate agreement will not just safeguard the environment," Ban, who visited the Arctic ice rim where he saw first-hand the devastating effects of climate change on the glaciers, emphasized." It can help to fundamentally shift our world toward a greener economy."