A new round of UN climate talks got under way on Monday to appeals for action and compromise after the squabbles that drove last year's global summit in Copenhagen close to disaster.
"A richer tapestry of efforts is needed," UN climate chief Christiana Figueres warned, as she spelt out the tasks facing the 12-day conference in the Mexican resort city of Cancun.
"A tapestry of holes will not work -- and the holes can only be filled in through compromise."
President Felipe Calderon of Mexico, whose country is hosting the conference, also appealed for common purpose.
"Climate change is already a reality for us," he told delegates. "During the next two weeks, the whole world will be looking at you. It would be a tragedy not to overcome the hurdle of national interests."
The Executive Secretary of the United Nations Framework Convention on Climate Change (UNFCCC).
RajendraPachauri, chairman of the UN's Intergovernmental Panel on Climate Change (IPCCC), warned of the penalties if the world dragged its feet.
The more man-made carbon gases that enter the atmosphere, the greater the warming of Earth's atmosphere and the worse the consequences for the planet's climate system, he said.
"Global emissions should peak no later than in 2015 and decline thereafter," he said, referring to the least costly scenario for averting drought, flood, rising seas and storms.
"Delays in action would only lead to impacts of climate change which would be much larger and in all likelihood more severe than we have experienced so far. These impacts are likely to be most severe for some of the poorest regions and communities in the world."
The talks, held under the 194-party UN Framework Convention on Climate Change (UNFCCC), are being attended by around 15,000 delegates, grass-roots campaigners and journalists.
Mexican police and troops, supported by three warships, threw a security cordon around the Moon Palace hotel, a luxury beachfront complex.
The conference is part of an arduous process to craft a post-2012 treaty for curbing carbon emissions and channelling hundreds of billions of dollars in aid for badly-exposed poor countries.
In some quarters, the November 29-December 10 parlays are seen as the last chance to restore faith in a process battered by finger-pointing and nit-picking.
It comes almost a year to the day since a stormy summit in Copenhagen, where a last-minute, face-saving compromise was lacerated by critics as a betrayal.
That trauma, coupled to economic crisis, caused climate change to almost disappear off the political radar screen, with the only prompts for action coming from the record heatwaves in Russia and floods in Pakistan.
In the UNFCCC, meanwhile, negotiations have switched from a big vision to securing visible progress in small, practical steps.
Work in Cancun will focus on securing agreements, at least in principle, for setting up a "Green Fund" to help poor countries, preventing carbon emissions from deforestation and encouraging the transfer of clean technology from advanced economies.
Decisions could be made singly or in a package, Mexican Foreign Minister Patricia Espinosa told a press conference.
"Cancun is the litmus test. We will see if governments are willing to protect their citizens through international cooperation," said Gordon Shepherd of green group WWF.
"This year has seen massive suffering and loss due to extreme weather disasters. This is likely to get worse as climate change tightens its grip," said Tim Gore of the British NGO Oxfam.
In Geneva, the UN's special rapporteur on the right to food, Olivier De Schuetter, urged the Cancun conference to launch a "Green Marshall Plan" to combat the rising threat of hunger from climate change.
The IPCC estimates that yields from rain-fed agriculture could be cut by up to half between 2000 and 2020, while arid and semi-arid areas could grow by 60 million to 90 million hectares.
That could put 600 million more people at risk of hunger, De Schuetter said.