The climate deal reached in Paris is "the best chance we have to save the one planet we have", US President Barack Obama has said.
He said it could be a "turning point" towards a low-carbon future.
China, the world's biggest polluter, also hailed the deal, as did India. But some campaigners said it did not go far enough to protect the planet.
The Paris pact aims to curb global warming to less than 2C (3.6F) by the end of the century.
Nearly 200 countries took part in tense negotiations in the French capital over two weeks, striking the first deal to commit all nations to cut emissions.
The agreement - which is partly legally binding and partly voluntary - will come into being in 2020.
'Almost nothing binding'
Describing the agreement as "ambitious", President Obama said: "Together, we've shown what's possible when the world stands as one."
"In short, this agreement will mean less of the carbon pollution that threatens our planet and more of the jobs and economic growth driven by low-carbon investments."
However, Mr Obama admitted that the pact was not "perfect".
China's chief negotiator Xie Zhenhua agreed that the Paris plan was not ideal. But he added that "this does not prevent us from marching historical steps forward".
China earlier said rich developed countries needed to offer more financial support to developing countries.
India's Prime Minister Narendra Modi said there were "no winners or losers".
"Climate justice has won and we are all working towards a greener future," he tweeted.
Giza Gaspar Martins, the chairman of the group representing some of the world's poorest countries, said: "It is the best outcome we could have hoped for, not just for the Least Developed Countries, but for all citizens of the world," he said.
But Nick Dearden, director of campaign group Global Justice Now, said: "It's outrageous that the deal that's on the table is being spun as a success when it undermines the rights of the world's most vulnerable communities and has almost nothing binding to ensure a safe and liveable climate for future generations."
An organisation of business leaders that pushes for industry to be more sustainable, WBCSD, said, in a tweet, that the agreement shows "the transition to a low carbon economy is unstoppable".
Some aspects of the agreement are legally binding, such as the obligation on individual countries to set an emissions reduction target and the regular review of that goal.
However, the targets themselves will not be legally binding under the Paris deal.
The measures in the agreement included:
• To peak greenhouse gas emissions as soon as possible and achieve a balance between sources and sinks of greenhouse gases in the second half of this century
• To keep global temperature increase "well below" 2C (3.6F) and to pursue efforts to limit it to 1.5C
• To review progress every five years
• $100bn a year in climate finance for developing countries by 2020, with a commitment to further finance in the future.
Analysis: The BBC's Matt McGrath in Paris
The speeches and the cliches at the adoption of the Paris Agreement flowed like good champagne - success after all has many fathers! The main emotion is relief. The influence of the COP president, Laurent Fabius, cannot be overstated. His long diplomatic career gave him a credibility seldom matched in this arena. He used his power well.
The deal that has been agreed, under Mr Fabius, is without parallel in terms of climate change or of the environment. It sets out a clear long-term temperature limit for the planet and a clear way of getting there. There is money for poor countries to adapt, there is a strong review mechanism to increase ambition over time. This is key if the deal is to achieve the aim of keeping warming well below 2C.
More than anything though the deal signifies a new way for the world to achieve progress - without it costing the Earth. A long term perspective on the way we do sustainability is at the heart of this deal. If it delivers that, it truly will be world changing.
Observers say the attempt to impose emissions targets on countries was one of the main reasons why the Copenhagen talks in 2009 failed.
At the time, nations including China, India and South Africa were unwilling to sign up to a condition that they felt could hamper economic growth and development.
The latest negotiations managed to avoid such an impasse by developing a system of Intended Nationally Determined Contributions (INDCs).
In these, which form the basis of the Paris agreement goal of keeping global temperature rise "well below" 2C above pre-industrial levels, nations outline their plans on cutting their post-2020 emissions.
UN climate conference 30 Nov - 11 Dec 2015
COP 21 - the 21st session of the Conference of the Parties - will see more than 190 nations gather in Paris to discuss a possible new global agreement on climate change, aimed at reducing greenhouse gas emissions to avoid the threat of dangerous warming due to human activities.
Explained: What is climate change?
In video: Why does the Paris conference matter?
Analysis: Latest from BBC environment correspondent Matt McGrath
In graphics: Climate change in six charts
More: BBC News special report (or follow the COP21 tag in the BBC News app)