By Valerie Volcovici and Alister Doyle
LIMA (Reuters) - As UN climate talks enter their final days, the "Berlin Wall" that has for years divided rich and poor countries once again looms large as negotiators race to write a draft of a global deal that is meant to tear it down.
At the root of the problem is a 1992 U.N. climate Convention splits the world into rich and poor nations and obliges only the rich to cut emissions. Since then, however, nations such as Singapore or Mexico have grown rich but are still deemed "poor".
In Lima, representatives of 192 countries are trying to craft a new accord that will hold developed nations responsible for their past emissions but that will also put on the hook some emerging economies that will emit most carbon in future.
Last month progress was made to break down barriers between rich and poor – defined in UN jargon as annex 1 and non-annex 1 - when the United States and China announced joint action to curb emissions across a divide sometimes called a "Berlin Wall".
Countries are grappling with how to redefine these distinctions in a draft deal to be finalized in Paris next year that is meant to limit more heat waves, floods, desertification and rising sea levels.
EU Energy and Climate Commissioner Miguel Arias Cañete warned Wednesday that some countries are propping up the firewall in the final days of talks. "Some parties have unfortunately reverted to standard positions," he said.
Saudi Arabia's chief negotiator Khalid Abuleif stressed to reporters that the division between developed and developing countries should continue, "but we are open to discussing that, to ensure broader participation."
Indian Environment Minister Prakash Javadekar said in a speech Wednesday that Lima talks were not the "right time or process to discuss these issues."
U.S. Special Envoy on Climate Change Todd Stern, who has also spoken in the past of a "Berlin Wall, said retaining divisions defined in 1992 was politically "untenable" when the world economy has changed so radically.
Yvo de Boer, a former U.N. climate chief, said the wall between rich and poor started to crumble at talks in Bali in 2007 when governments launched talks on a global climate pact.
"I think the Berlin Wall was knocked over in 2007. There have been some very active bricklayers trying to put it back up," he said.
The U.S. and China agreement said a 2015 climate deal should honor the "principle of common but differentiated responsibilities and respective capabilities, in light of different national circumstances." This phrasing could be a template for Paris, Stern said.
As negotiators haggled, the president of the summit tasked the ministers who arrived in Lima this week to meet in informal groups to hash out ideas for addressing what those responsibilities mean for all.
These consultations are meant to give negotiators the "political direction" that's needed to address the "well-known splits and very different opinions," said Alden Meyer, director of strategy and policy at the Union of Concern Scientists.
Figuring out how to break down that wall in time for Paris will be crucial for addressing the main sections of the agreement - mitigation, adaptation and finance, observers said.
While some developing nations favor the traditional divide, others have made symbolic moves to break it down.
Mexico, Peru and Colombia on Wednesday announced they would contribute $22 million to the UN's Green Climate Fund, meant to help developing nations combat global warming, even though they are themselves defined as poor under the 1992 jargon.
Meanwhile, Brazil has tried to make its mark on the UN talks by floating a plan it said would create a more fluid scheme to let developing countries gradually increase their obligations.
"In our proposal there are no walls. This is a way to break the gridlock, preserving the convention but allowing, over time," countries to take on more obligation," Brazil's lead negotiator Ambassador Antonio Marcondes said.
He said the idea is gaining traction among other countries.
Proposals like Brazil's are a sign that the wall is on track to crumble before Paris, said Nathaniel Keohane, a vice president at the Environmental Defense Fund.
"There were fissures in the wall and now they have been broken open," he said.
(Reporting By Valerie Volcovici; editing by Andrew Hay)