If a climate deal is to be done, it is more likely to be thrashed out over coffee in the corridor, a glass of wine at dinner or a stroll along Copenhagen's cobbled downtown streets than in the vast conference hall.
Personal chemistry and friendships among opposing delegates are critical in complex negotiations, and could be particularly crucial this weekend when ministers from key countries try to break through the deadlocks in talks on a global accord to control greenhouse gases responsible for climate change.
The ministers were coming earlier than planned to prepare the ground for a summit of 110 leaders at the end of the week. The aim is to tie up a political deal laying the outlines of a new climate change pact that will be finished next year.
The Copenhagen conference caps two years of negotiations among 192 countries. They have convened for formal talks nearly a dozen times, usually getting nowhere. But their leaders or top negotiators have met even more often in informal settings _ touring a South African wildlife park, walking on an Argentinian glacier or relaxing near the fjords of Greenland.
Those weeks of relaxed conversations, discussions of families and hobbies alongside climate issues and public policy, swapping suits for jeans, are invaluable in building relationships and trust that can translate in the future into diplomatic breakthroughs.
Two of the bitterest foes in the negotiations, U.S. special envoy Todd Stern and Chinese negotiator Xie Zhenhua are known to meet regularly and cordially, even though they communicate through an interpreter.
"He's a very personable guy," Barbara Finamore, China program director for the Natural Resources Defense Council, says of Xie. She says the two men have an understanding that goes deeper than their public positions.
The Copenhagen conference, like all U.N. climate talks before, are conducted on many levels, from the open assemblies attended by all nations to small rooms where a few delegates haggle in quiet.
Public negotiating sessions often are contentious rounds of finger-pointing couched in diplomatic niceties. Poor countries say they will be the first to suffer from global warming caused by the rich industrial world. Wealthy nations say developing countries are not doing enough to help solve the problem.
The nations are grouped in various alliances with common interests, the largest known as the G-77 plus China which actually is comprised of some 135 countries. The G-77 is joined by the European Union, the Small Island States, the Least Developed Countries and the Umbrella Group, which lumps the United States with Australia, Canada and Japan.
It's a convenient way to save time and repetition, with an appointed spokesman stating an agreed position at the opening or closing of a plenary.
The plenary sessions are not for negotiation. It's where nations stake out positions, posture for their home constituency and show allegiance to their allies. Delegates say most of the progress is hammered out behind the scenes.
"The more intimate the setting, the easier it is to talk," said Jurgen Lefevere, a veteran European climate negotiator. "It's amazing how much depends on who bumps into who in the corridor."
Plenary sessions break up into smaller "contact groups" to deal with specific issues. When talks bog down, the chairman may assign a "friend of the chair" to pull the key players into a side room and thrash it out. If that fails, the problem will be put aside for later. If it's a major issue, it will wait be passed up to the ministers or heads of government.
The formal and informal streams reinforce each other, Lefevere said.
In smaller groups negotiators can probe, parry and question. They explore how far the other side can relent and where the threshold of pain is, said Lefevere, a Belgian diplomat representing the European Commission.
One-on-one contact can be over coffee at the conference center or over a glass of wine and a good dinner.
This is when delegates exchange hard information or privately swap internal documents and proposals, Lefevere said. "You get the nuances and subtleties that you can't convey in a big meeting."
But even with friends, he said, "you have to be careful how to show the bottom line."