A last-minute deal that salvaged U.N. climate talks from collapse early Sunday sends a signal the rich-poor divide that long held up progress can be overcome with a year to go before a landmark pact is supposed to be adopted in Paris.
Still, it remains to be seen whether governments can come up with a new formula for how countries in different stages of development should contribute in a way that keeps global warming from reaching dangerous levels.
"This issue will be contentious and it will need to be worked through all the way to Paris," U.S. climate envoy Todd Stern said after the marathon talks in Lima finished, more than 30 hours behind schedule.
The U.N. talks were still far away from reaching any agreement on reducing emissions of carbon dioxide and other greenhouse gases to a level that scientists say would keep global warming in check. But the Paris agreement would be the first to call on all countries to control their emissions.
The U.S. and other developed nations say that means tearing down the firewall in negotiations that compels only rich countries to rein in emissions of carbon dioxide and other greenhouse gases.
Though it was agreed in 2011 that goals set in Paris would be "applicable to all," many developing countries worry they will be required to take on emissions controls that stymie their economic growth. In Lima they angrily rejected a draft text that made no mention of different responsibilities and capabilities to fight global warming.
"We are in a differentiated world. That is the reality," Malaysian negotiator Gurdial Singh Nijar told delegates. "Many of you colonized us, so we started from a completely different point."
Despite the tough rhetoric, the conference ended Sunday with a compromise based on a groundbreaking U.S.-China deal on emissions targets last month.
The Lima decision noted the principle in the 1992 U.N. climate change convention that countries have "common but differentiated responsibilities" to tackle climate change. But like the U.S.-China deal, it added that this should be seen "in light of different national circumstances," suggesting countries' responsibilities change over time as they develop.
"It sounds like a tiny thing, but it's very important," said Nathaniel Keohane, vice president of the Environmental Defense Fund. "I think we're starting to see the plates move."
How to interpret what it means in practice is going to be critical over the next year as countries firm up their emissions targets for the Paris agreement.
Asked about the implications of the Lima deal, Chinese negotiator Su Wei repeated China's mantra that the purpose of the Paris agreement is to "reinforce and enhance" the 1992 convention, not rewrite it.
"This paragraph may represent a compromise that both sides can interpret as they choose to," said Alden Meyer of the Union of Concerned Scientists.
Yet the joint announcement with the U.S. signaled that China is ready to assume a bigger role in the global response to climate change. For the first time, the world's biggest carbon polluter set a fixed target to peak emissions by 2030.
Showing signs that it, too, anticipates the end of a binary view of the world, Brazil put forth a proposal of "concentric circles" with different expectations for developed, emerging economies and least-developed countries.
The final agreement in Lima didn't address Brazil's proposal, though it noted that climate action plans by least-developed countries and small island nations should reflect their "special circumstances."
All countries are supposed to present their plans to control emissions before the Paris agreement next year. In Lima, negotiators listed things that countries "may" want to include in their pledges, such as time frames, base years and methods for calculating emissions.
China and other developing countries blocked a proposal for a review process that would allow the pledges to be compared against each other. Instead, the U.N. climate agency will prepare a report analyzing the "aggregate" effect of all pledges a month before Paris.
Meanwhile, rich countries resisted any firm commitments of money to help poor countries tackle climate change, though many separately announced pledges to a Green Climate Fund set up for that purpose.
Environmental groups worried the outcome of the Paris talks will be a purely voluntary system where both developed and developing countries propose weak voluntary actions without regard to the deep emissions cuts scientists say are needed to avoid dangerous levels of warming.
Emissions keep rising every year because cuts in rich countries aren't enough to offset fast growth in China, India and other emerging economies. Meanwhile, climate impacts ranging from sea level rise and increasingly freakish weather are becoming more noticeable as warming continues. This year could go down as the hottest on record.
"Political leaders at the U.N. talks need to be reminded that they can't negotiate with the climate," said Mohamed Adow, a climate change expert at Christian Aid. "Otherwise we're in danger of sleepwalking into a failed deal in Paris."
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