Ministers from around the planet today launched a five-day scramble in Paris to answer "the call of history" and strike a deal to spare mankind from climate disaster.
The 195-nation UN talks in Paris have been billed as the last chance to avert the worst consequences of global warming: deadly drought, floods and storms, and rising seas that will obliterate islands and densely populated coastlines.
"The clock is ticking towards a climate catastrophe," UN Secretary-General Ban Ki-moon told ministers, who face a Friday deadline to reach an accord that has proved elusive in more than two decades of wrangling.
"The world is expecting more from you than half-measures and incremental approaches," Ban warned.
"It is calling for a transformative agreement. Paris most put the world on track for long-term peace, stability and prosperity."
He added: "The decisions you make here will reverberate down the ages."
Environment and foreign ministers, including US Secretary of State John Kerry who landed in Paris today, were urged to rise to the moment and rip out hundreds of bracketed words or sentences in the draft accord that denote disagreement.
"The opportunity to rise to the call of history is not given to everyone or every day," UN climate chief Christiana Figueres told the conference.
"History has chosen you here, now."Elusive target
Taking effect from 2020, the Paris accord would seek to limit emissions of heat-trapping greenhouse gases, driven especially by coal, oil and gas -- the backbone of the world's energy supply today.
The goal of the negotiations is to limit global warming to less than 2.0 degrees Celsius (3.6 degrees Fahrenheit) above pre-Industrial Revolution levels.
But scientists say the planet is already halfway to the 2 C figure, which means that the rise in fossil-fuel emissions must peak soon, and go quickly into reverse, to meet the precious objective.
The talks opened November 30 with a record-breaking gathering of 150 world leaders who issued a chorus of warnings about mankind's fate if planet warming went unchecked.
After a week of talks, negotiators met a Saturday deadline to produce a draft 48-page blueprint that agreed on the need for urgent action but left unresolved many of the deep and complex divisions that condemned previous UN efforts to failure.
Among the slew of fundamental issues in dispute are how far and how fast to limit global warming, and how to check on what countries are doing to curb their greenhouse gas emissions.
Another potential deal-buster is money.
Rich countries promised in 2009 to muster $100 billion (92 billion euros) a year by 2020 to help developing nations make the costly shift to clean energy, and cope with the impacts of climate change.
But specifically how the promised funds will be raised remains unclear -- and developing countries are also pushing for a promise that the money will be ramped up beyond 2020.
Small island states that risk being swamped in a warmer world have pressed for a more ambitious accord limiting planetary warming to less than 1.5C.
"If we save Tuvalu we save the world," Tuvalu Prime Minister Enele Sosene Sopoaga told the conference.
Thoriq Ibrahim, the environment minister of the Maldives and chair of the Alliance of Small Island States, said the Paris event was the "last opportunity for the world to seal the agreement we desperately need".
Ban urged nations to be bold, pressing ministers to agree to five-year reviews of the deal, and to initiate the scrutiny even before it comes into effect in 2020.
The goal would be to strengthen greenhouse gas-cutting commitments as needed to curb planetary overheating, guided by new science and new technologies.Money the 'glue' of Paris deal
Oxfam's head of advocacy and campaigns, Celine Charveriat, described the issue over funding for developing nations as "the glue that will make the Paris agreement stick".
"It will be the difference between a minimalist agreement and one that starts to deliver for the world's poorest people," she said.
Negotiators also emphasised that, despite overwhelming goodwill among negotiators, extremely tough talks lay ahead.
"Let's be frank: all the difficult political issues remain unresolved," European Climate and Energy Commissioner Miguel Arias Canete said at the weekend.
Offering a gloomy but timely picture of the world's future if global warming went unchecked, a "red alert" for air pollution was issued in the Chinese capital of Beijing today.
As winter coal burning for heating escalated in Beijing, authorities warned people to stay indoors and ordered many factories to close. Half of Beijing's private cars will also be ordered off the roads from Tuesday.