Kerry, who chairs the Senate Foreign Relations Committee, said he was encouraged by his recent discussions in Beijing with senior Chinese officials, business leaders and scientists on the issue.

"Our words and our actions will set the tone," he said at a hearing with experts on China and climate change. "Washington and Beijing will inevitably lead by example."

With the world's largest economy, the United States has historically been the biggest emitter of the greenhouse gases blamed for climate change, but it recently has been overtaken by China.

The United States and China alone are responsible for nearly half the planet's carbon emissions, said Kerry.

"Either we will create the necessary momentum to finally galvanize a global response, or else we risk a global catastrophe," he said.

"My message to the Chinese was simple: America understands that we have an obligation to lead. But you need to understand that, politically speaking, America will not enter into a global treaty without a meaningful commitment from China to be part of the solution," he said.

The committee's ranking Republican, Senator Dick Lugar, said China's responses to climate change to date have been "complex and contradictory."

"The American domestic debate on the issue will be profoundly influenced by perceptions of China's willingness to set aside doctrinaire positions and agree to verifiable steps to limit greenhouse gas emissions," he warned.

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