Ban Ki-moon, the secretary-general of the United Nations, has called on world leaders to confront a global warming "crisis" and show "strong political commitment" and compromise in dealing with it.
Speaking at the annual UN climate talks in Doha, Ban noted that there were "mixed feelings" among delegates who were negotiating deals, but that the situation posed an "existential challenge for the whole human race".
"This is a crisis," said Ban on Tuesday, as a string of scientific reports warned the world could be headed for calamitous warming way above the limit of two degrees Celsius (3.6 Fahrenheit) being targeted by the UN.
Climate change poses "a threat to us all. Our economies. Our security. And the well-being of our children and those who will come after," said the UN chief.
About 100 ministers and a handful of heads of state are in the Qatari capital for the final, high-level stretch of the talks that have so far been marked by disputes over cash and commitments required to curb rising greenhouse gas emissions.
'Abnormal is new normal'
After more than a week of tough talks that run until late at night, observers say delegates remain far apart on issues vital for unlocking a global deal on climate change.
Poorer countries have insisted that industrialised nations must sign up to deeper, more urgent cuts in carbon emissions under a follow-up, second commitment period for the Kyoto Protocol.
They have also called for a new 2013 funding package to help cope with worsening drought, flood, storms and rising seas.
Ban urged the parties to "work with a spirit of compromise", and cited tropical storm Sandy, which struck the US east coast and the Caribbean last month, killing dozens of people, as a "call to action".
"The abnormal is the new normal," Ban said. "It is an existential challenge for the whole human race - our way of life, our plans for the future."
The Doha negotiators, he said, must reaffirm their commitment to a follow-up for Kyoto, which runs out on December 31, to reaching a new, universally-binding climate pact for 2020, and to climate funding for the poor world.
Ban said that the technology and know-how existed to achieve the conference's goals - the only thing lacking was political will.
Al Jazeera's Nick Clark, reporting from Doha, said that now that ministers and other senior officials have arrived, more pressure is being applied to reach a conclusion to talks.
"[There are] three days [left] to take on three main prongs of attack: the first is extending the Kyoto Protocol; the second is finding a roadmap to a universal agreement in 2015 for implementation in 2020; and the third is sorting out the complex world of climate finance," he said.