World nations have launched a new round of talks in Warsaw to pave the way for a 2015 deal to cut climate-altering greenhouse-gas emissions.
The 12-day United Nations Climate Change Conference began on Monday in Poland's capital amid a slew of warnings about a potentially disastrous rise in greenhouse-gas emissions.
Though no major decisions are expected at the conference, the level of progress could be an indicator of the world's chances of reaching a deal in 2015, which is the new landmark year in the UN-led process after a 2009 summit in Copenhagen ended in discord.
Global greenhouse gas emissions need to peak this decade, and get to zero net emissions by the second half of this century.
Climate change is "very, very scary stuff. And evidence is accumulating weekly, monthly as to how dangerous this will be. So there is a huge urgency that we get on with this," said Andrew Steer, the head of the World Resources Institute in Washington.
Key details of the new treaty remain to be worked out, including whether all or parts of it should be legally binding.
It is also unclear in what form national offers of post-2020 emissions cuts and other climate actions will be presented and by when.
Many key players, including the European Union, are pushing for countries to present their initial offers at a climate summit for world leaders called by UN Secretary-General Ban Ki-moon in September next year.
"In Warsaw, we must agree to prepare strong pledges for the 2015 deal and to step up emission cuts over the rest of this decade," EU Climate Commissioner Connie Hedegaard said.
Negotiators will face a host of recurring stumbling blocks, including money to help poor countries convert to cleaner energy sources and adapt to a shifting climate that may lead to disruptions of agriculture and drinking water, and the spread of diseases.
The urgency of the problem was underlined in a recent report by the Intergovernmental Panel on Climate Change, the UN-sponsored body that provides the scientific basis for the negotiations.
The IPCC said in September with more certainty than before that humans are warming the planet, mainly through carbon emissions from the burning of oil, coal and gas.
It raised its projections for sea-level rise and warned that the Arctic Ocean could be nearly ice-free during summers before mid-century if the world did not act to curb emissions.
"Global greenhouse gas emissions need to peak this decade, and get to zero net emissions by the second half of this century," UN climate chief Christiana Figueres said on Thursday.
But the hard part is deciding how to divide those cuts. Since they began in 1992, the UN talks have been bogged down by disputes between rich and poor countries over who should do what.
While many countries say the US must do more, increasing focus is falling on the world's top carbon polluter, China, which is under pressure to fuel its economic development in a cleaner way than the US and other industrialized nations did.