Calling global climate change a "life-threatening issue," Secretary of State nominee John Kerry said Thursday that the United States must play a key role in reducing greenhouse gas emissions that contribute to global warming.

Kerry, a Massachusetts Democrat, said at his confirmation hearing that the U.S. should pursue policies to boost clean energy and energy efficiency. In his state and others, such as California, "the fastest growing sector of our economy is clean energy," Kerry said. "It's a job creator."

Kerry, chairman of the Senate Foreign Relations Committee, has made climate change a central focus of his Senate career and led a failed effort in the Senate for a climate change bill in 2010.

Kerry told fellow senators he would be a "passionate advocate" on the issue if confirmed as secretary of state, "not based on ideology but based on facts, based on science. And I hope to sit with all of you and convince you that this $6 trillion (energy) market is worth millions of American jobs and leadership, and we better go after it."

Failing to deal with climate change was more of a risk than addressing it head-on, Kerry said, citing damage caused by Superstorm Sandy, drought and wildfires. Congress is expected to approve more $50 billion in disaster relief for Sandy victims alone. The storm pounded Northeastern states in late October and has been blamed for 140 deaths.

"If we can't see the downside of spending that money" as a short-term fix after a disaster "and risking lives for all the changes that are taking place — to agriculture, to our communities, the ocean and so forth, we're ignoring what science is telling us," Kerry said.

On a related issue, Kerry said he has made no decision about the Keystone XL oil pipeline from Canada. Environmental groups have been pressuring the Obama administration to reject the pipeline, saying it would carry "dirty oil" that contributes to global warming.

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Kerry said a review process is well underway at the State Department. The department has jurisdiction over the pipeline because it crosses an international border.

"It will not be long before that comes across my desk," Kerry said. "And at that time, I'll make the appropriate judgments about it."