GENEVA, SWITZERLAND — In what many observers are already calling the most significant environmental accord since the Paris Agreement, representatives from 195 countries emerged from five days of exhausting negotiations on Sunday with a deal that imposes legally binding emissions targets on the world's largest economies.

The agreement, reached just before 3 a.m. local time at the Palais des Nations, was greeted by a prolonged standing ovation from the assembled delegates — and by urgent warnings from climate scientists that even this hard-won consensus may not be enough to prevent the most catastrophic effects of global warming.

Under the terms of the agreement, the 40 nations responsible for more than 85% of global greenhouse gas emissions must submit updated nationally determined contributions by 2027, with each country required to demonstrate a credible pathway to net-zero emissions by 2045 at the latest.

"This is not a voluntary compact among polite nations," said the chief UN climate negotiator, Dr. Amara Diallo. "This agreement has teeth. For the first time in the history of international climate diplomacy, there are real consequences for inaction."

Talks almost collapsed on Thursday evening when a bloc of major oil-producing nations threatened to walk out over language requiring the 'phase-out' of fossil fuels. The final text instead calls for a 'managed and accelerated phase-down' of unabated fossil fuel use.

Perhaps the most contentious element of the final agreement is the climate finance package. Developed nations have committed to mobilising $500 billion annually by 2030 to help poorer countries adapt to climate impacts and decarbonise their economies.

"The science is clear: we are at 1.6°C of warming. Every fraction of a degree of additional warming will cost us dearly. This agreement is the floor, not the ceiling, of what we need to do," said Dr. Diallo.

For many of the world's most vulnerable nations — small island states, sub-Saharan countries, coastal communities already experiencing the effects of rising seas — the response to the deal was one of grim, qualified relief.

"We came here asking for survival," said the Prime Minister of the Marshall Islands, visibly emotional after the vote. "We leave with something less than that, but more than we feared. The work is far from finished."