Initiated by Ban Ki-moon, Secretary General of the United Nations, the UN Climate Summit brought together a hundred Heads of Governments, alongside the financial world, business and civil societies to give new momentum to the search for answers to the challenges posed by climate change.

The event opened with speeches by the UN Secretary-General, Mayor Bill de Blasio, as well as former Vice President Al Gore and actor Leonardo de Caprio, followed by interventions from Heads of State, including President Obama of the United States and President Hollande of France. The Director-General of UNESCO attended the Summit throughout the discussions.

The Summit saw pledges and new commitments from many participants. For instance, New York City Mayor Bill de Blasio announced that New York City is committed to reducing greenhouse gas emissions by 80 per cent by 2050, while a coalition of more than 200 mayors, representing 400 million people, pledged to sign a Mayor’s Compact to reduce annual emissions by between 12.4 and 16.4 per cent.
The Climate Science session of the Summit showcased how climate science can inform actions that support this goal, providing an interactive discussion of the science – policy interface and emphasising the need for urgent decisions underpinned by scientific findings.
Chaired by the Presidents of Mongolia, H.E. Mr Tsakhigiin Elbegdorj, and Guyana, H.E. Mr Donald Ramotar, this high level session was addressed by  Aleqa Hammond, Premier of Greenland (Denmark), Thomas Stocker, Co-chair of the Intergovernmental Panel on Climate Change (IPCC) Working Group I, Julia Marton-Lefèvre, Director General of the International Union for the Conservation of Nature (IUCN), and Barbara Frost, Chief Executive of WaterAid.
The President of Mongolia opened the session by underlining that "climate science is critical to the future of the planet -- this is why this Climate Change Summit is an opportunity we cannot miss."
This was followed by an interactive discussion that focussed on the key findings of climate science relevant to policy, as well as how to harness knowledge and information more effectively and to educate and empower people for action. Linking the findings of science with policy is the role of the Scientific Advisory Board for Sustainable Development for the UN Secretary-General, steered forward by UNESCO, who hosts its secretariat.
Ms Hammond made the stakes clear -- "We are experiencing climate change in our bodies, in our minds, in our country every day."
These issues were explored by Ms Frost from the angle of water -- "urgent action is needed for 750 million men and women without access to safe water."
The debate included interventions from participants from across the world, including the Prime Minister of Tuvalu and John Holdren, Assistant to to the US President for Science and Technology as well Professor E. Kalnay, from Argentina, member of the Scientific Advisory Board to the UN Secretary-General.
Speakers underlined that access to sound science, information and climate services is crucial to long term effective climate action. This calls for greater investment to further enhance knowledge and to reduce uncertainty, through stronger science and tighter links with policy.
The discussion highlighted also that the knowledge base for informed action is already available to guide climate policies and decisions from the national to the local scale -- but this must be harnessed fully and nurtured by all actors.
Mr Stocker said the impact of climate change is clear and unequivocal. Science is clear in showing the warming of the climate system, with unprecedented changes over decades to millennia, and that human influence is the dominant cause. Staying within the internationally-agreed 2 degree Celsius temperature rise limit -- itself with a deep impact -- can only be realized through urgent and ambitious action to move towards carbon-neutral economies and societies. A higher rise will have a tremendous impact on the planetary ecosystems.
Avoiding the worst impacts will require substantial and sustained reductions in greenhouse gas emissions starting now.
Ms Marton-Lefèvre underlined the importance of partnership for joint action. "We need science to demonstrate it is good for nature and for the people who depend on it," she said.
Ms Hammond said it all, expressing the thoughts of all present:
"Sustainability, sustainability, sustainability is the answer."

For fererence:
The Summit precedes the United Nations Climate Change Conference on the United Nations Framework Convention on Climate Change, which will take place between 30 November and 11 December 2015 (COP21) in Paris (France). The Conference is a platform for intergovernmental negotiations aimed at creating a new international agreement on climate change, keeping the global warming below 2°C.

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