Tempers flared in Copenhagen today as protesters were beaten back by police outside the Bella Center, where the international climate talks were taking place. The police used tear gas to subdue the protests, and they arrested around 250 people.

But the turmoil wasn't limited to the outside of the Bella Center. The chairwoman of the conference, Connie Hedegaard of Denmark, announced that she was stepping down and handing the reins to Lars Locke Rasmussen, the Danish prime minister. "With so many heads of state and government having arrived it's appropriate that the Prime Minister of Denmark presides," she said, calling the move procedural.

Amid the upheaval, some negotiators have grown bearish about the prospects for a climate agreement. “There are many details that aren’t getting resolved and I’m not sure two days is enough time,” said Tarja Halonen, the president of neighboring Finland. “The atmosphere here has declined." But she remains "cautiously optimistic" that President Obama can breathe new life into the talks when he arrives on Friday.

Of course, Obama's encouragement will mean little if the United States Senate is unable to pass a meaningful domestic climate bill. That's why Sen. John Kerry (D-Mass.) took to the conference floor this morning in an effort to persuade delegates that American climate legislation is indeed forthcoming, echoing the message his colleague Barbara Boxer delivered two days earlier. But he also stressed the importance of commitments by China and other countries in order to convince reluctant U.S. senators that America will not bleed jobs by acting alone.

China, however, remains critical of any agreement that will allow an international team to inspect and verify its emissions regulations. That could be a major sticking point as negotiations move toward the finish line.

Despite all these hiccups, UN climate chief Yvo de Boer is emphasizing that there's still plenty of room for optimism. "I still believe it's possible to reach a real success," he said. "The next 24 hours are absolutely crucial."

The prospects for a unified front between developed and developing nations in combating climate change further broke down today, as more than half of the world's countries -- mostly smaller nations, including those most threatened by the effects of global warming -- pledged not to sign any accord that allows global temperatures to rise by more than 1.5 degrees Celsius. (Abhishek's got more on that)

The target currently espoused by the world's leading economies is 2 degrees. Reducing that figure by half a degree could require an additional investment of $10.5 trillion by 2030 to stabilize carbon in the atmosphere at 350 parts per million, lower than the current level of 387.

The pledge to limit an emissions increase to 1.5 degrees was announced by the 43-member Alliance of Small Island States (Aosis), following a similar move by the tiny island nation of Tuvalu yesterday, and backed by other developing nations. But it's highly unlikely that the world's leading emitters will commit to the kind of reductions that would enable a 1.5-degree target. Even the push to contain temperature increases to 2 degrees faces an uphill battle.

Meanwhile, the European Union, whose emissions targets have come under criticism, scrambled to come up with a game plan for the upcoming days of the conference, when key decisions will be made. The central issues for the EU are how sharply to curb greenhouse gas emissions and how much money to give poorer nations so they can cope with the effects of climate change.

The latter issue received additional attention today when George Soros unveiled a new proposal today that he says would free up $100 billion without adding to the donor countries' deficits. “Developed countries’ governments are laboring under the misapprehension that funding has to come from their national budgets, but that is not the case—they have it already,” Soros said. “It is lying idle in their reserves accounts and in the vaults of the International Monetary Fund.”

The climate conference itself is again facing criticism, this time for its own contribution to carbon emissions. According to The New York Times, the conference will generate 40,500 metric tons of carbon dioxide equivalent.

But some good news for environmentalists came out of the United States today, when a tripartisan group of senators unveiled their framework for a domestic climate bill. Their move could lend more legitimacy to President Obama's pledges, which some fear will be undermined by a recalcitrant Congress. Need a reminder of just how important the United States is to global emissions levels? Look no further than this map.

The delegates have descended on Copenhagen. The curtain has been raised. And as UN climate chief Yvo de Boer told the representatives of 192 countries at the opening festivities of the 12-day international climate conference, “The clock has ticked down to zero. After two years of negotiation, the time has come to deliver.”

Momentum is on their side. After months of stagnation, culminating in the Nov. 14 decision not to attempt a legally binding, comprehensive climate treaty at Copenhagen, the past week has brought a flurry of positive developments for environmentalists seeking to reduce the world's greenhouse gas emissions. India has pledged an emissions target, following similar announcements by the United States and China. President Obama has decided to attend the last day of the conference, when final decisions will be made, rather than making a one-day stop in Copenhagen this Wednesday en route to Oslo. And in another demonstration of his commitment to progress in Copenhagen, Obama will meet today with former Vice President Al Gore, a fierce environmental advocate who himself will attend the conference, to discuss strategy going into the talks.

This morning, an editorial ran in 56 newspapers in 45 countries calling on the world's developed nations to commit to "deep cuts which will reduce their emissions within a decade." Delegates themselves are seeking to send a powerful message to the conference; 400 of them arrived in Copenhagen this weekend on board the carbon-neutral Climate Express.

Of course, the rollout of the Copenhagen talks has not been without problems. With protests expected, security has been a major issue, and demonstrators have taken issue with Denmark's wildly ramped-up security operation. And conservative media outlets have highlighted the specter of the "Climategate" scandal, which threatens to hover over the negotiations, despite the continued scientific consensus that man-made global warming is a real and serious threat to the planet.

While a final climate treaty is not expected until next December, the next two weeks promise to lay the groundwork and answer crucial questions about the prospects for global consensus.

We'll have daily updates here at UN Dispatch that will provide easy-to-digest roundups of the days' activities and developments. 

Having scaled back their ambitions for next month's Copenhagen climate conference, world leaders are working to salvage the effort, and some are optimistic about the prospects for a meaningful step toward a legally binding international climate treaty.

Prime Minister Kevin Rudd of Australia -- which despite its low profile has the highest per-capita emissions of any developed country -- told the BBC on Monday that "there is a strong and high degree of political resolve among many of the leaders around the world to land a Copenhagen agreement." Friis Arne Petersen, the Danish ambassador to the United States, channeled Barack Obama when he declared in The New York Times on Monday, "Yes we can reach a strong, comprehensive and global agreement next month."

But all eyes remain on the two biggest emitters in the world, the United States and China. The countries' leaders agreed to "a series of important new initiatives" last Tuesday in Beijing and vowed to "work toward a successful outcome in Copenhagen," although their agreements remained vague. In a more concrete pledge, the White House has announced that its delegation to Copenhagen will propose a numeric figure for emissions reduction.

“The one thing the president has made clear is we want to take action consistent with the legislative process,” an administration official told ABC News on Monday. “[We] don’t want to get out ahead or be at odds with what can be produced through legislation. And so whatever number we put on the table will be with reference to what can come out of the legislative process.” That figure is likely to resemble the 17-percent reduction by 2020 laid out in the bill passed by the House of Representatives in June.

Still unknown is whether Obama himself will attend the conference. In keeping with Obama's line from two weeks ago, a White House official says that the American president will go only if his presence can provide "a final impetus, a push, to the process." ABC reports that Obama will make his decision in "the coming days."

One potential wrinkle: Last week, hackers obtained and released thousands of emails from a climate research center in England, revealing some awkward -- but not quite incriminating -- exchanges between climate scientists. Global warming skeptics are citing these communications as proof of fraudulent scientific evidence of climate change, while one of the scientists suspects that the leak was deliberately timed to sabotage the Copenhagen conference, telling the AP, "It is right before the Copenhagen debate, I'm sure that is not a coincidence."