Delegates from almost 200 countries have extended until 2020 the Kyoto Protocol for fighting climate change.
The document, adopted in 1997, was due to expire by the end of the year.
The extension was agreed at a United Nations climate conference in Doha, Qatar, that concluded on December 8.
The meeting, scheduled to have concluded a day earlier, was extended as rich and poor nations faced off on sticking points, including the Kyoto deal, finance, and compensation for climate damage.
The president of the Doha Climate Conference, Abdullah Bin-Hamad Al-Attiyah, said the deal reached in Doha would serve as a "gateway" for future action to combat global warming.
"I called the result of this conference the 'Doha Climate Gateway.' And what I meant is the gateway to the future. [A] gateway even beyond 2020," he said.
Britain's minister for climate change, Ed Davey, was upbeat over the outcome of the conference.
"It's not just about paving the way for 2020, it is about increasing ambitions now in the run-up to 2020," Davey said. "And I think there has been some steps in that direction. So I think that is positive and I know some people will be disappointed and would want more. The U.K. and the EU have always been on the ambitious side of things, but we are moving as a world and it's important that the world moves in the right direction and it did here in Doha."
However, environmentalists, including Greenpeace activist Kumi Naidoo, said the new deal would do little to halt a rise in temperatures or avert more natural disasters.
"Our governments must realize that this failure is a betrayal of the people in the Philippines and around the world that have faced climate impacts now, today, and will continue in the days to come," Naidoo said. "But what is at stake here is not some ethereal thing called the planet, the climate, the environment. But what is at stake here is selling down our children's and grandchildren's futures."
The Doha Climate Gateway was approved with the 27-member European Union, Australia, Switzerland, and eight other industrialized nations signing up for binding emissions cuts by 2020.
The move averted a new setback to two decades of UN efforts that have failed to curb rising greenhouse gas emissions.
The Kyoto Protocol thus remains the only legally binding plan for fighting climate change.
However, it only covers about 15 percent of global emissions after Canada, Japan, New Zealand, and Russia opted out.
The United States never joined Kyoto, in part because it did not include China and other fast-growing developing economies.
UN Secretary-General Ban Ki-moon welcomed the decision agreed in Doha but said it was just a first step toward expanding the fight against global warming.
Ban spokesman Martin Nesirky said nations must do "far more" to stop climate change. Nesirky quoted Ban as saying that the Doha Climate Gateway should lead the way to "a comprehensive, legally binding agreement by 2015."
Nations aim to adopt in 2015 a wider treaty that would apply to all countries after the Kyoto extension expires.
With reporting by AP, Reuters, and AFP