"I do think it's objectively true that our country is the only country in the world that can really lead the global community," Gore said in testimony to the Senate Foreign Relations Committee on the need to battle global warming.

"Some have speculated that sometime in the future, if the European Union actually unifies to a much higher degree, and has a president, and an effective legislative body that has real power, they might somehow emerge, with potential for global leadership. I'm not going to hold my breath," he said.

"I don't want to be too proud, you know, to be chest-beating about that, but I think the United States is the only nation that can lead the world," Gore told the panel.

"And this is the most serious challenge the world has ever faced" apart from the "receding" threat of nuclear war, he said. "This is the one challenge that could completely end human civilization."

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