Environmental groups say nations have reached a deal to limit the use of greenhouse gases far more powerful than carbon dioxide as part of efforts to fight climate change.

At issue are hydrofluorocarbons, or HFCs, which are used in air conditioners and refrigerators. Observers say the agreement, set to be announced early Saturday, would cap the use of HFCs beginning in 2019, led by developing countries. Developing countries including China would start taking action in 2024.

Observers say a small group of countries including India and some Middle East states pushed for and secured a later start, arguing that their economies need more time to grow.

Scientists have said an agreement could put a half-degree Celsius dent in global warming by the end of the century.