Delegates at a United Nations-sponsored conference in Paris have adopted a global pact to reduce climate change.
Nearly 200 nations adopted the document -- described as the first climate deal to commit all countries to cut emissions -- on December 12 after two weeks of negotiations. It is to come into force in 2020.
The text sets the objective of making sure that global warming stays "well below" 2 degrees Celsius and continuing to "pursue efforts" to limit the temperature rise to 1.5 degrees Celsius. Temperatures have already increased by 1 degree Celsius since pre-industrial times.
To achieve that goal, governments pledged to stop the rise in greenhouse gas emissions "as soon as possible." By some point after 2050, man-made emissions should be reduced to a level that nature can absorb.
However, there is no penalty for countries that miss their emission-reduction targets.
The measures also include $100 billion a year in climate finance for developing countries by 2020, with a commitment to increase the figure in the future.
Delegates rose to their feet cheering and applauding as French Foreign Minister Laurent Fabius struck the gavel to signal the adoption of the deal.
"Together we've shown what is possible when the world stands as one," U.S. President Obama said in a news conference hailing the breakthrough in Paris.
While not "perfect," he said, "this agreement represents the best chance we have to save the one planet that we've got."
Obama claimed the agreement came as a result of his turning the United States into a world leader on climate change during his years in office, coaxing all nations to contribute to a solution, and it will be one of his most "important" legacies.
German Chancellor Angela Merkel called the pact an "historical turning point," and said she was pleased "the global community has for the first time committed itself to the fight against global climate change."
"History will remember this day," UN Secretary General Ban Ki Moon said. "The Paris agreement on climate change is a monumental success for the planet and its people."
(Left to right:) Christiana Figueres, executive secretary of the UN Framework Convention on Climate Change, United Nations Secretary-General Ban Ki-moon, French Foreign Affairs Minister Laurent Fabius, and French President Francois Hollande applaud during the final plenary session at the World Climate Change Conference 2015, which approved a new environmental agreement in Paris on December 12.
Most environmental activists reacted positively to the agreement, which replaces the 1997 Kyoto Protocol, but warned it was only the first step of many.
"Today the human race has joined in a common cause, but it's what happens after this conference that really matters," Kumi Naidoo of Greenpeace said. "This deal alone won't dig us out the hole we're in, but it makes the sides less steep."
“World governments finalized a global agreement today in Paris that lays a foundation for long-term efforts to fight climate change," the WWF conservation group said.
However, it also warned that "more effort is needed to secure a path that would limit warming to 1.5C."
Commenting before the approval of the pact, some environmental groups had said the final draft agreement would be a huge blow to the fossil-fuel industry.
"The wheel of climate action turns slowly, but in Paris it has turned," Greenpeace International executive director Kumi Naidoo said. "This deal puts the fossil-fuel industry on the wrong side of history."
According to May Boeve, executive director of 350.org, an organization pressing financial institutions to divest from fossil fuels, "There is no way to meet the targets laid out in this agreement without keeping coal, oil, and gas in the ground."