ROME — The Group of Eight summit in L'Aquila, Italy, underlined how the G8 nations and emerging powers must cooperate to drink from the same well.

Yet the crucial event of the three-day meeting in central Italy was the failure of the Major Economies Forum on Energy and Climate, or MEF, to agree to halve greenhouse gas emissions by 2050.

The meeting was not aided by the sudden departure Wednesday of Chinese President Hu Jintao, who returned home to deal with ethnic riots in Urumqi, the capital of the Xinjiang autonomous region in northwestern China.