Attempts to forge a new climate treaty failed in Copenhagen three years ago, but countries agreed last year to try again, giving themselves a deadline of 2015 to adopt a new pact.
Several issues need to be resolved by then, including how to spread the burden of emissions cuts between rich and poor countries. That's unlikely to be decided in the current talks in the Qatari capital of Doha, where negotiators from nearly 200 countries are focusing on extending the Kyoto Protocol, and trying to raise billions of dollars to help developing countries adapt to a shifting climate.
"We owe it to our people, the global citizenry. We owe it to our children to give them a safer future than what they are currently facing," said South African Foreign Minister Maite Nkoana-Mashabane, who led last year's talks in Durban, South Africa.
The U.N. process is often criticized, even ridiculed, both by climate activists who say the talks are too slow and by those who challenge the scientific near-consensus that the global temperature rise is at least partly caused by human activity, primarily the burning of fossil fuels like coal and oil.
The concentration of greenhouse gases such as carbon dioxide has jumped 20 percent since 2000, according to a U.N. report released last week. The report also showed that there is a growing gap between what governments are doing to curb emissions and what needs to be done to protect the world from potentially dangerous levels of warming.
"Climate change is no longer some distant threat for the future, but is with us today," said Greenpeace climate campaigner Martin Kaiser, who was also at the Doha talks. "At the end of a year that has seen the impacts of climate change devastate homes and families around the world, the need for action is obvious and urgent."