Peru's Minister of Environment Manuel Pulgar Vidal, center, speaks next to U.N. official Christina Figueres ,left, during a news conference at a climate conference in Lima, Peru, on Dec. 1. (Ernesto Benavides/AFP/Getty Images)

The Obama administration is hoping for fresh momentum toward a climate treaty during international talks this week in the Peruvian capital, but the immediate challenge may be to simply keep the negotiations from breaking down.

Officials from 190 countries gathered in Lima on Monday for 12 days of meetings intended to lay the foundations for a carbon-cutting pact that would be signed a year from now in Paris. But achieving even modest progress will require overcoming stark differences over what the accord should look like and who should pay for implementing it, diplomats acknowledged as the talks got underway.

On an opening day infused with ceremony and symbolism—including the unfurling of a protest banner by the environmental group Greenpeace on a hill overlooking the famous Machu Picchu ruins — U.S. officials expressed guarded optimism, saying prospects for a climate deal have brightened substantially in the wake of last month’s U.S.-China agreement on cutting greenhouse gas emissions.

But the officials acknowledged that old disputes over money and fairness carried the potential for sabotaging the negotiations, as they have during previous attempts to forge a deal.

“There is an opportunity here — probably more of an opportunity than there has been for a very long time,” said Todd Stern, the State Department official who is leading the U.S. negotiating team in Lima. “But that opportunity is going to be contingent on countries acting with a degree of balance and pragmatism that can allow this agreement to get done.”

(Patterson Clark / The Washington Post/Source: United Nations)

The U.N.-sponsored talks in Lima are intended to resolve technical and financial issues in advance of final negotiations for a treaty that would be signed in Paris next December. A successful effort, diplomats say, will put the world’s nations on a path toward rapidly reducing emissions of carbon dioxide and other gases that scientists say are contributing to a dangerous warming of the planet.

At the opening sessions Monday, several diplomats pleaded for unity in addressing what some described as the greatest environmental peril in human history.

“As the people on the front lines of this crisis, we know all too well that the world is still well short of the level of action needed to avert catastrophe,” said Marlene Moses, a diplomat from the Pacific island nation of Nauru and the leader of a group of small island states that are being threatened by rising sea levels. “If we don’t bring emissions down immediately, well before 2020, the opportunity to avoid the worst impacts, including the total inundation of small islands, may be irrevocably lost.”

Last month’s U.S.-China agreement provided an important boost to the talks as the world’s top two emitters agreed to unprecedented steps to lower carbon pollution over the next 15 years. Scores of other countries are expected to follow suit over the coming months as the diplomats begin the process of transforming individual commitments into a global treaty achieved through international consensus.

But enormous obstacles remain, as countries and political blocs maneuver to ensure that their interests are protected. Among the thornier questions to be addressed in Lima is whether limits on carbon emissions should be legally binding. Many smaller and poorer countries insist on legal accountability to ensure that wealthy countries honor their pledges to reduce pollution, while the United States and other Western powers are less enthusiastic about legally binding commitments that would probably face heavy opposition from legislatures back home.

Equally daunting is the question of financing. Developing countries have insisted that the biggest historic polluters — chiefly the United States and Europe — should pay substantial sums to help poorer countries make the transition to renewable energy while also protecting them from the effects of global warming. The United States last month committed to contributing $3 billion to a nearly $10 billion Green Climate Fund intended for just that purpose. But some of the intended recipients have demanded that the world’s biggest polluters fork over far greater sums, arguing that the West is morally obligated to clean up a problem that is mostly of its own making.

Still other countries — particularly major oil producers — see any serious climate treaty as a direct threat to their economic well-being. Saudi Arabia and other Persian Gulf states have sought to play spoiler during past climate talks, demanding that any climate treaty include compensation to countries that could be the biggest losers in a transition to a carbon-free global economy.

(Patterson Clark / The Washington Post/Source: IPCC Fifth Assessment Synthesis Report)

“There are a whole bunch of things that could upset the apple cart,” said Paul Bledsoe, a former environmental adviser to the Clinton administration and now a senior fellow at the German Marshall Fund.

Bledsoe said the greatest single threat to the Lima talks is a walkout by developing countries that “see the negotiations as a last chance to achieve a measure of climate protection and financing.” But there are multiple opportunities for conflict when the negotiators represent such vastly different perspectives and interests, he said.

“The divide between the major emitters and negligible emitters is going to be fulcrum of dissension,’’ Bledsoe said. “Overcoming it will require the sides to really negotiate in good faith. But that’s really hard to do when your negotiators are 190 different countries.”