Long-running arguments over who needs to do what to stop the planet from overheating are back in focus this week as rich and poor countries meet in Bonn, Germany, to resume talks on a new global climate treaty.
It's the first major round of talks since countries agreed in Durban, South Africa, in December to come up with a binding agreement by 2015 that would take effect five years later.
In a webcast news conference Monday, U.N. climate chief Christiana Figueres noted that the cuts in greenhouse gas emissions pledged so far fall short of what scientists say is needed to avoid serious effects of global warming.
But she said "bridging the gap is both technically attainable and economically feasible" if rich countries, in particular, raise their ambitions on emissions cuts.
The talks have been hampered by bickering over how to divide such cuts among developing nations, emerging economies and industrialized countries.
That's not going to be resolved in the two-week negotiations in Bonn or at a bigger climate summit in Qatar at the end of the year.
But climate negotiators hope to build on the modest progress that was achieved last year, like the agreement on a second commitment period for the Kyoto Protocol, a treaty which limits the emissions of most developed countries but which expires at the end of this year. The length of the second commitment period is one of the issues on the table in Bonn.
However, Kyoto plays an increasingly marginal role in the climate puzzle because it doesn't include the biggest emitters of carbon dioxide and other gases that scientists say contribute to global warming.
The U.S. pulled out of Kyoto, saying it was unfair because it didn't impose any emissions reductions on fast-growing developing nations such as China and India. Canada announced it would withdraw from the treaty last year.
The new treaty being negotiated would require all nations to take action to curb warming. Specifying those requirements is a major challenge, which is why negotiators tend to focus on solving incremental, less contentious issues, first.
"First and foremost we have to ensure that there is no backtracking on what was agreed in Durban," said Christian Pilgaard Zinglersen, a Danish official representing the European Union.
Meanwhile, climate activists warned that potentially catastrophic consequences of global warming, including floods and droughts and rising sea levels, will be impossible to prevent unless the negotiations speed up.
"If you look at the science, we're spending time we don't have," said Tove Ryding, the climate policy coordinator of environmental group Greenpeace.