ROME — With the relevance of the Group of Eight being challenged by emerging powers, the G8 leaders got down to business Wednesday addressing climate change and what their next move might be when and if the global recession subsides.

But the launch of the three-day G8 summit in L'Aquila was spoiled even before it began, with Chinese President Hu Jintao returning home to get a handle on the ethnic riots tearing apart the restive city of Urumqi in the northwest.

A shadow also grew over the climate change issue as chances appeared slim that the Major Economies Forum on Energy and Climate, or MEF, would be able to hammer out long-term greenhouse gas emissions cuts, Japanese diplomatic sources said.