COPENHAGEN -- If the talks that resulted in an imperfect deal to combat global warming provided anything, it was a glimpse into a new world order in which international diplomacy will increasingly be shaped by the United States and emerging powers, most notably China.

Friday's agreement, sources involved in the talks said, boiled down to President Obama and Chinese Premier Wen Jiabao personally hammering out a pact both could live with, even if many other leaders could not. Wen even squelched his own negotiator's protests.

What Obama heralded as a "breakthrough" -- after getting India and other rising powers to sign on -- was decried by some nations as too little, too late. The leaders of Europe, Japan and other countries at the summit were largely left to rubber-stamp the deal. The Swedish prime minister's office dubbed it "a disaster."

Ever since the concept of a G2was proposed this year by former U.S. national security adviser Zbigniew Brzezinski, the idea that the United States and China together are going to solve all the world's problems has been pooh-poohed by both American and Chinese officials. China hated the notion because it put too much responsibility on a country that has done very well rising in the shadows. Many U.S. officials opposed the idea on the grounds that the best way to influence China was through multinational partnerships.

So, more than anything else, critics said, Friday's climate agreement reflected the domestic political realities in Washington and Beijing. Both nations, the two biggest emitters of greenhouse gases, remain more cautious than, say, the governments of Europe about establishing a strict set of international rules to combat global warming. Not coincidentally, the agreement allows nations to set their own emission reduction targets and provides no deadline for signing a binding international accord.

A shifting relationship

As such, the deal may portend how issues from world trade to nuclear proliferation will be negotiated in the years ahead, with China leading a caucus of rising powers on one side and the United States on the other.

"The mark is being stamped on a new political world," said Duncan Marsh, who directs international climate policy for the Nature Conservancy. Said Jake Schmidt, international climate policy director for the Natural Resources Defense Fund: "Coming into this conference, it was about 193 countries, and coming out of it, it clearly came down to a conversation between the leaders of those two superpowers."

Orville Schell, a longtime China watcher who is director of the Center on U.S.-China Relations at the Asia Society, said the erratic dance between China and the United States is another example of how the bilateral relationship is at a tipping point. China is becoming a major player, albeit reluctantly; the United States, with similar unease, is making room for China at the table of world leaders.

"We're not exactly partners, but we're much more equals," Schell said. "The Chinese miss the idea that there's some grander, stronger authority. They are not used to this role of actually helping to fashion and form things."

Indeed, the events at the summit showed how the U.S.-China relationship remains stormy and complex, constructive and adversarial. At one point in Friday's tense talks, for instance, China's top climate change negotiator exploded in rage at U.S. pressure after Obama walked in on the Chinese while they were holding talks with the Indians, South Africans and Brazilians. After Obama asked whether the Chinese could commit to listing their climate targets in an international registry, Xie Zhenhua launched into a tirade, pointing his finger at the U.S. president.

A compromise from China

The United States had made any deal contingent on international verification of emission cuts made by nations, seeing it as key to winning over skeptical lawmakers on Capitol Hill who are still resistant to sweeping climate change legislation at home. But there was no way China would agree to international verification, Xie told the Americans.

It was a position that China had held to closely over months of negotiations with the United States and other countries. China's vice minister of foreign affairs, He Yafei, had reiterated it just hours earlier.

But this time, something different happened, according to Chinese and Western sources close to the talks. Wen instructed his Chinese interpreter not to translate Xie's fiery remarks. When Xie erupted again, Wen, who was chairing the meeting, ignored him. After Wen handed Obama a draft text of an agreement that included verification language Obama couldn't abide by, the two men led a lengthy debate that ended in a working compromise, sources said.

China has a long history of opposing verification, seeing it as a violation of its sovereignty. It has also used the sovereignty argument as a way to cover up for failures or weaknesses. When China tracked air pollution in Beijing in the run-up to the 2008 Summer Olympics, for instance, authorities in the capital moved monitoring stations into areas with less congestion to get positive ratings. When the U.S. Embassy in Beijing established an air-quality monitoring site on its grounds -- and began sending pollution readings out on Twitter -- the Chinese took umbrage and implied that the action was an interference in their country's internal affairs. Twitter later was blocked nationwide.

But on Friday, Wen ultimately agreed to stronger verification language. By the nature of the agreement, however, China's participation will be voluntary.

The fate of any future global climate change treaty will now effectively rest in the hands of the two largest emitters. For at least the next several years, the lack of a binding international treaty may result in a piecemeal response to the problem, with action being taken largely on a national and regional level.

Yet proponents of the Copenhagen agreement stress that the Obama administration is taking unprecedented action at home, pushing for a national switch to green energy and for a cap-and-trade system that could help dramatically curb emissions.

Wen, according to several Americans who have interacted with him on this issue, is also passionate about climate change. He chairs a high-level Communist Party group on climate change, which sets policy and makes major decisions.

In addition, Ken Lieberthal, a former senior director for Asia at the National Security Council who is now a China expert at the Brookings Institution, said that for China to even tentatively agree on an international verification regime and on the necessity of registering its climate goals marks substantive movement.

"Of course you could say, 'It's just words; they won't do anything,' " Lieberthal said. "But words matter internationally. You can hold people to their words and shame them if they don't comply."