WASHINGTON - A trio of climate change meetings in the United States this week will focus attention on how Washington can deliver on its pledge to play a lead role in combating global warming.

A NASA satellite image from September 21, 2005 and released on September 21, 2007 shows Arctic summer sea ice coverage in 2005. Arctic sea ice melted to its lowest level ever this week, shattering a record set in 2005 and continuing a trend spurred by human-caused global warming, scientists said on September 20, 2007. [Reuters]

The central issue is how to curb the emission of climate-warming greenhouse gases, especially carbon dioxide from coal-fired power plants and petroleum-fueled vehicles, and whether to make the goals mandatory or "aspirational" as the White House has proposed.

As the world's leading emitter of greenhouse gases, the United States has said it wants to lead, but critics from the US environmental movement and elsewhere question whether its voluntary approach will work.

A "high-level" UN meeting in New York on Monday is meant to send a "strong political message" from world leaders, according to UN Secretary-General Ban Ki-moon, although it is not a negotiation on climate change.

Harlan Watson, the chief US climate negotiator, said it was time to move beyond talk and try to develop a way forward.

"We're getting beyond the conceptual ... level and want to get down to the kind of roll-up-your-sleeves stage," Watson said on Friday at a briefing. "We really want to get away from the dialogue ... and see how we can really construct an architecture for what happens after the first commitment period of Kyoto ends in 2012."

The United States is at odds with the Kyoto Protocol, an international agreement that requires 36 industrial nations to cut greenhouse emissions by at least 5 percent from 1990 levels by 2012, when the protocol expires.

GETTING READY FOR BALI

Climate change negotiations will take place in December in Bali, when representatives will consider a way to cut emissions after the Kyoto pact expires. The deadline for figuring this out is 2009, so countries have enough time to ratify the agreement.

Eighty-one heads of state or government will attend Monday's event, along with two vice presidents, five deputy prime ministers, 33 foreign ministers and 12 environment ministers, in addition to 18 other representatives, according to the United Nations. Former US Vice President Al Gore and California Gov. Arnold Schwarzenegger are scheduled to attend.

Bush will not attend but is scheduled to dine with Ban afterward, in advance of his address on Tuesday to the UN General Assembly.

Bush will speak at a two-day Washington meeting at the State Department on Thursday and Friday, a gathering of "major economies" -- which are also the world's biggest global warming contributors -- on energy security and climate change.