China and the United States took a major step in the fight against climate change over the weekend, but what was termed a "breakthrough" might not do much in the longer term to lock in legally binding carbon emission cuts from the world's two biggest emitters of greenhouse gases.

 

Still, environmental groups and some U.S. and global policymakers said the agreement could give fresh momentum to the United Nations' arduous process of finalizing a global treaty to replace the Kyoto Protocol on climate change by 2015.

 

In their first talks, U.S. President Barack Obama and Chinese Premier Xi Jinping agreed to phase out production and consumption of the gases known as hydrofluorocarbons (HFCs), working under the U.N's 1987 Montreal Protocol.

 

Used mostly in air conditioners and refrigerators, ozone-harming HFCs make up roughly 2 percent of greenhouse gas emissions, but are rising at a rate of up to 9 percent annually.

 

The White House said a global phase-down could reduce the carbon dioxide equivalent of 90 billion tons by 2050, roughly two years worth of global greenhouse gas emissions.

 

Analysts worry that the U.N. climate talks continue to be hampered by deep divisions between developed and developing countries over the responsibility for carbon emissions.

 

One official close to the negotiations said the agreement was a political breakthrough, but the road ahead to a global deal on climate change would still be long.

 

The official said the weekend agreement, which followed earlier talks between Secretary of State John Kerry and Xie Zenhua, a vice chairman in China's top economic development body, can inject a dose of optimism into the U.N. climate talks. But the deal represents a powerful example of what can be done when two major powers work together, the official added.