Melt runoff from Exit Glacier in Kenai Fjords National Park. About ten years ago, this spot would have still been part of the glacier. (Official White House Photo by Pete Souza)

By Coral Davenport and Gardiner Harris

 LE BOURGET, France — One of the largest gatherings of world leaders in history began a multinational effort Monday toward forging what many called the planet’s last, best hope to stave off the worst consequences of climate change.

“Never have the stakes of an international meeting been so high, since what is at stake is the future of the planet, the future of life,” President François Hollande of France told a packed United Nations plenary session at a convention center in this suburb north of Paris.

Over the next two weeks, 30,000 diplomats and delegates will labor to hammer out a new global pact that would, for the first time, commit nearly every country on earth to enact new policies to reduce their planet-warming greenhouse gas emissions.

Mr. Obama said that the United States was at least partly to blame for the life-threatening damage that environmental change has wrought.  “I’ve come here personally, as the leader of the world’s largest economy and the second-largest emitter,” Mr. Obama said, “to say that the United States of America not only recognizes our role in creating this problem, we embrace our responsibility to do something about it.”

Still, huge hurdles remain ahead of striking a deal, which must be agreed to unanimously by the nearly 200 countries in order to be legally binding.

The greatest threat to reaching a binding climate accord may be a loose coalition of developing nations, led by India, who argue that they should not be asked to limit their economic growth as a way of fixing a problem that was largely created by the others. Mr. Obama conceded that point.

With India the world’s third-largest greenhouse gas polluter, Mr. Obama has invested heavily in his relationship with Prime Minister Modi in hopes of securing his cooperation for a deal here.

Besides the officials from all over the world, the event is expected to get a lift from prominent business leaders and philanthropists. Some of them are using the talks to announce substantial donations to help the cause of reducing emissions, developing alternative energy sources, conservation, and aiding poor and low-lying countries expected to be most affected by climate change.

The Breakthrough Energy Coalition, a group of business and philanthropy executives led by the Microsoft founder Bill Gates, who have a combined total of $350 billion in private wealth, has pledged to invest in moving clean-energy technologies from laboratories to the marketplace.

It is hoped that the pledge, along with one by 19 countries, including the United States, to double their investments in energy technologies to $20 billion by 2020, will help convince poor countries that they will be given significant help in making a transition to a new economic model that relies less on the use of carbon.

In one of many such expected announcements, the State Department pledged $248 million to help the world’s least-developed countries move toward a future that is less reliant on carbon.

This is the largest gathering of world leaders in two decades. Many leaders are seeing the urgency and they have a new optimism that a successful deal could be closer at hand than ever before.

Read more and watch videos at The New York Times

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Tags: Paris climate change conference, President Obama