When siblings argue, there can be an intensity unlike that in any other sort of argument because, if for no other reason, they are stuck with each other -- family.
There is also, say psychologists, the potential for great liberation, once existential realities are accepted and, when possible, embraced.
The last full day of the Copenhagen climate summit -- Friday, Dec. 18 -- saw such an argument on an unprecedented scale.
With 128 heads of state or government having gathered in one place (a record, according to the United Nations), they broke into smaller groups throughout the day for sometimes contentious meetings in which these world leaders themselves did the tough word-for-word haggling over texts that is usually handled by aides.
It was more global than any international debate in history, at least in the sense that it was the first among so many world leaders that concerned the bedrock habitability -- for humans and many other species -- of the only home we've got.
This debate was within what is at times called The Family of Man.
At the moment, it appears that Mother Earth and Mother Nature are at the head of the table.
And as President Obama quoted at some point months ago, "If Mama ain't happy, ain't nobody happy."
But some eminent American climate scientists are greatly encouraged by the high-level arguments that took place -- often simply because they did.
Central among these day-long wranglings were a meeting between the leaders of China, the United States, India, Brazil and South Africa, as well as other meetings involving those five and some 25 other leaders.
"I have never seen anything like it," U.N. Secretary General Ban Ki Moon told ABC News 36 hours later on a plane flying back to New York. "It makes a big difference when the top leaders talk to each other."
At one point at a bargaining table, as one participant who was in the room told ABC News, Obama leaned over to Secretary of State Hillary Clinton, sitting to his left, and said, only somewhat sotto voce, "I'm trying to be constructive here, but I'm losing patience."
At another point, as The Washington Post reported, "After Obama asked whether the Chinese could commit to listing their climate targets in an international registry, Xie Zhenua ... China's top climate negotiator [who had already] exploded in rage at U.S. pressure ... launched into a tirade, pointing his finger at the U.S. president."
But then a remarkable thing happened.
China's Premier Wen Jiabao, reported to be "passionate" about the urgent need for action on global warming, instructed the translator not to translate what Xie had said.
Perhaps Xie's tone and body language made any translation unnecessary.
Nor does it seem probable that the Americans or their friends in the room would not have included someone who understood Chinese.
It wasn't too long after that, as an official who was in the room told ABC News, that Wen "suddenly offered a slight change of tone that made things possible" and suggested that there could, after all, be a sort of language on the vexed "transparency" issue that China might live with.
"A little window," said this official, holding his hand up with the tips of his thumb and index finger barely an inch apart, "but enough."