AMSTERDAM — Next month's climate summit in Copenhagen, Denmark, seeks to transform the way the planet is run, from the production of energy, to the building of homes and cities, to the shaping of the landscape. It also would shift wealth from rich to poor countries in the process.
No wonder a deal will be difficult to cut.
In recent weeks, prospects brightened, then dimmed, then revived again.
President Obama dampened expectations when he said during his Asian tour that a final package could not be completed at the conference. He then lifted hopes by signaling the United States might go further in the talks in the Danish capital than had been expected because of lagging U.S. legislation.
Hoping to nudge negotiations, principal governments have strengthened pledges to control their nations' greenhouse gases, the heat-trapping emissions blamed for global warming.
Still, everyone is waiting to see what the United States will do.
The major economies "are coming to Copenhagen ready to fill in the blanks. They are all looking to see what happens in Congress, and what the U.S. is able to bring to the table," said climate analyst Jennifer Morgan of the World Resources Institute, a Washington think tank.
Facing mounting impatience, the U.S. delegation could bring a provisional number to the conference, promising at least a 17 percent cut in greenhouse gases over the next decade, measured against 2005 — a number drawn from bills awaiting congressional approval.
"It's a bit of a balancing act," said U.S. analyst Alden Meyer, of the Union of Concerned Scientists. The Obama administration wants to satisfy the international demand for clarity without seeming to pre-empt U.S. lawmakers, "providing ammunition for opponents in the Senate."
More than 65 heads of government will attend the final days of the Dec. 7-18 conference, investing their personal prestige in the outcome. They include the leaders of Britain, France, Germany, Australia, Brazil, Indonesia, Japan and Spain.
Success is a matter of definition. Two years ago, when negotiations began, delegates anticipated a full treaty would be signed in Copenhagen to succeed the 1997 Kyoto Protocol, which set emissions limits on 37 industrial countries. The United States rejected Kyoto because it imposed no obligations for China, India and other rapidly emerging economies.
Now the Danish hosts and the United Nations say it will be enough to nail down all the political elements, leaving the details, technical issues and legal language to be filled in over the following six months to a year.
Many developing countries say that is not good enough and insist Copenhagen aim for a full-fledged legal document.