Negotiators from 158 countries reached basic agreement Friday on rough targets aimed at getting some of the world’s biggest polluters to reduce emissions of the greenhouse gases blamed for global warming.

A weeklong U.N. climate conference concluded that industrialized countries should strive to cut emissions by 25 percent to 40 percent of their 1990 levels by 2020. Experts said that target would serve as a loose guide for a major international climate summit to be held in December in Bali, Indonesia.

The agreement does not include the U.S., which has not ratified the Kyoto Protocol.