WASHINGTON - International climate talks in Lima, Peru, are entering their final week, with few hints of whether a newfound optimism that marked the start of negotiations will translate into an agreement that would rein in climate change.

Convened by the United Nations, the talks aim to craft the framework for an international accord to curtail heat-trapping emissions and adapt to changes already occurring on the planet. The final agreement is due to be signed in Paris next December.

Despite more than 20 years of discussions about what nations must do to contend with climate change, the world's emissions of carbon dioxide and other heat-trapping gases are higher than ever, as negotiations have continued to snag on the contradictory priorities of different countries.

The latest round in the discussions began last week with fresh momentum, in large part thanks to steps the U.S. took last month, including a major deal with China to curb emissions and a $3 billion commitment to help developing nations fight climate change.

Yet, over the days since the Lima conference began Dec. 1, clashes have flared between developed and developing countries over issues such as whether emissions cuts should be mandatory and how much money rich countries should provide to help poor nations.

Many conflicts stem from countries hewing to familiar hard-line bargaining positions. The question remains whether the brinkmanship will give way to an agreement by the end of the week on key issues.

"It's disappointing that countries can't rise above these petty differences," Jake Schmidt, international climate-policy director for the Natural Resources Defense Council, said from Lima. "But it's not surprising."

The window is closing fast for countries to cut greenhouse gases enough to avert the greatest global temperature increases and natural disasters associated with them, climate scientists and organizations such as the World Bank warn.