Europe has yet to see more "contribution" by the United States in the fight against climate change, Barroso told reporters before the G8 summit of leading industrialized nations in the northern German resort of Heiligendamm.

However, the recent U.S. plan on the issue is "a step in the right direction," and hopefully the Heiligendamm meeting can "make a difference" for climate change.

Still, the UN conference in Bali, Indonesia, scheduled in December, "has to remain the basis for setting binding, measurable and enforceable targets" to help stop global warming, he said.

Germany, which holds the rotating G8 presidency, calls for actions to limit the rise in global temperatures to two degrees Celsius this century and to cut carbon emissions by 50 percent below 1990 levels by 2050.

However, the United States, the world's biggest greenhouse gas producer, voiced opposition to the German proposal, making climate change one of the most controversial issues during the upcoming G8 summit.

Shortly before the summit, U.S. President George W Bush announced a separate plan, calling on 15 of the world's biggest greenhouse emitters to meet and agree on long-term goals by the end of 2008.

The United States, which has not signed the Kyoto Treaty, remains opposed to mandatory targets, citing that environmental protection cannot come at the price of hurting economic growth.

German Chancellor Angela Merkel said Wednesday that she expects "intensive debate" during the three-day summit which will focus on climate change, the development in Africa, the Doha Round of the World Trade Organization, the U.S. plan of deploying a missile defense shield in Central Europe.

Leaders from the G8 nations will kick off their annual summit later Wednesday.

The G8 club gathers Britain, Canada, France, Germany, Italy, Japan, Russia and the United States.