PARIS - President Obama sought to rally world leaders at a climate summit on Monday, declaring that ''no nation large or small, wealthy or poor, is immune'' to challenges such as global warming and urged political action even if the benefits are not seen for generations.
Quoting Martin Luther King Jr., Obama warned that ''there is such a thing as being too late.''
''And when it comes to climate change that hour is almost upon us,'' he added.
The president said that ''the United States not only recognizes our role in creating this problem, we embrace our responsibility to do something about it.'' But he stressed that all nations must act ''right now.''
The summit also opened chances for top-level dialogue on other fronts.
Sideline talks included a meeting between Obama and Russian President Vladimir Putin to discuss Syria's nearly five-year civil war and peace efforts in Ukraine between the Western-supported government and pro-Moscow rebels.
The two leaders agreed to re-launch bids to halt the fighting in Syria, but the two sides remain far apart on some key issues and no clear progress appeared to be made in Paris.
Russia says its military intervention in Syria seeks to cripple the Islamic State — a mutual enemy of Washington and its allies. But Moscow has heavily targeted rebel factions seeking to topple Syrian President Bashar Assad, a key Russian partner. In Paris, Obama repeated U.S. demands that Assad must eventually step down as part of any political transition.
Obama kicked off his day at the Paris gathering with a meeting with Chinese President Xi Jinping, hailing their mutual work on climate change but urging greater Chinese cooperation on cyber-crime and ''maritime'' issues that include China's military construction on disputed reefs in the South China Sea.
Putting China first on the schedule was an indication of China's central role on global issues such as climate change.
It was just a year ago that Obama and Xi vowed to set definite limits on the levels of greenhouse gas emissions, laying the foundation for other countries to follow suit. On Monday, Obama said: ''Our leadership on this issue has been absolutely vital.''
Other highlights of Obama's day here include a meeting with Indian Prime Minister Narandra Modi, whose government has been pressing for more financing and technology transfer.
Obama also will attend the formal unveiling of an initiative to boost research and development spending on new technologies, led by Bill Gates and a score of private investors. In addition, 19 countries have vowed to double their research and development spending. The summit will also feature a goal of a massive investment in solar power in countries closest to the equator.
''We have broken the old arguments for inaction,'' Obama said at the plenary session on Monday. ''We have proved that strong economic growth and stable investment no longer have to conflict with one another.''
Obama is one of about 150 world leaders at the Paris summit — formally known as the 21st Conference of Participants. Those leaders also delivered speeches.
''A political moment like this may not come again,'' said U.N. secretary general Ban Ki-moon. ''We have never faced such a test. But neither have we encountered such great opportunity.''
In the wake of terrorist attacks just two weeks ago, the conference has become a major security challenge and traffic has been blocked in Paris until Tuesday.
After arriving in Paris on Sunday, Obama's motorcade glided along the Seine through largely deserted streets before stopping in front of Le Bataclan, the concert hall where scores of people were killed in the terrorist attacks Nov. 13.
Flanked by French President François Hollande and Paris Mayor Anne Hidalgo, Obama placed a white rose on the street in front of the concert hall, making a small addition to the mound of flowers and candles there. After standing for a minute of silence with his hands folded before him, Obama walked away, briefly placing a hand on the shoulders of Hollande and Hidalgo.
Obama hopes to use his two days at the summit as a way of celebrating achievements made over the past several months, as well as negotiating with countries such as India, which is pressing for greater financial assistance and technology transfer.
The United States announced it will contribute $51.2 million to a $248 million Least Developed Countries Fund to help the world's poorest countries adapt to climate change. Germany is the largest of 11 donors to the fund.
''We know the truth - that many nations have contributed little to climate change but will be the first to feel its most destructive effects,'' Obama said.
But American officials said they would resist calls by many small island states and other countries vulnerable to climate change effects that developed nations pay reparations or damages due to their historic emissions. Those nations also favor setting a goal of limiting climate change to 1.5 degrees Celsius instead of 2 degrees. Obama will meet with island nations Tuesday.
Other countries used the conference to announce new details. Norway, Germany, and Britain said they would provide $1 billion a year until 2020 in payments for verified emissions reductions from forests and land use in other countries.