At a hearing of the Senate Environment Committee, Democratic Senator Hillary Clinton said after years of delay, global warming was "an issue whose time has come."

"If we look at where we are ... we are not making progress. In fact, emissions are still going up," she said.

"I'm hoping that we can get beyond the usual rhetoric and try to find some common ground," said Clinton, who currently leads the field of Democratic contenders for her party's 2008 presidential nomination.

The stepped-up concern came amid mounting calls for the United Nations to organize a world summit on climate change, and as a draft UN report concluded that global warming will unleash bouts of extreme heat, drought and rainfall and make typhoons and hurricanes more violent by 2100.

At the Senate hearing Tuesday, there was similar alarm.

"December in Minnesota felt more like October," said Democratic Senator Amy Klobuchar. "Our ice fishing seasons are shorter and our skiers and snowmobilers haven't seen much snow."

"Global warming is an issue that strikes us close to home. The stakes are as high as they get," she said.

President George W. Bush during his State of the Union speech last week unveiled a new energy initiative, but environmentalists were unimpressed, saying the United States needed to adopt policies capping emissions of greenhouse gases blamed for global warming.

Senator Barbara Boxer, the liberal Democratic new chairwoman of the environment committee, has vowed to hold a series of hearings on global warming in the coming weeks, and introduced a bill to raise energy efficiency standards for thousands of federal buildings.

A second bill she will soon introduce would step up development of cellulosic ethanol -- derived from agricultural waste, grass and other plants -- as an alternative to gasoline.

Boxer said America has a long way to go to catch up with much of the rest of the world in tackling climate change.

"Maybe we're the last ones to get on board here, but I think we're going to do it," she said.

Independent US Senator Joe Lieberman reintroduced a bill that would cap greenhouse gas emissions of the electric, industrial, transportation and commercial sectors at year 2004 levels by 2012, and would thereafter gradually lower the cap.

"Our bill uses the power of the free market to promote the rapid and widespread deployment of advanced technologies and practices for reducing greenhouse gases," he said.

"I believe the politics of global warning have changed and that a new consensus is emerging," said Lieberman.

US Senator Barack Obama said he is drafting a bill that would focus on improving fuel efficiency standards in the US car industry.

In addition to the economic and environmental benefits, conserving fossil fuel, Obama said, "gives us additional leverage in the Middle East, and can potentially go a long way in terms of reducing some of our military obligations around the world." "It's inexcusable for a country of our wealth and ingenuity and power not to be leaders," said the Illinois Democrat, who is just days away from what pundits believe will be a formal declaration later this month of his plan to run for the White House.

"We abdicated responsibility ... We were laggards on this issue," said Obama.

"This gives us an opportunity to show the world that we are prepared to work with them in a constructive, positive, but aggessive way," he said.

According to the UN draft report, there is now a 90-percent probability that man-made greenhouse gases have driven up Earth's surface temperature over the past half century.

Eleven of the last 12 years rank among the warmest years for which there are reliable records, according to the draft, which is being discussed line by line at the four-day meeting of the Intergovernmental Panel on Climate Change (IPCC) in Paris.

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