Soon after that, the official said, President Obama was talking to the cameras, then heading for the airport, hours behind schedule, and wheels up in hopes of beating the record snowstorm barreling down on Washington.
(Ironically, it was just the sort of "very heavy precipitation," whether rain or snow, long predicted by scientists to increase in frequency in the upper eastern and northeastern United States as a result of human-induced global warming, and which, over the past 30 years, has in fact materialized there. This can be seen on pp. 32 and 44, inter alia, in the US government's recent report, approved by 13 federal agencies, "Global Climate Change Impacts in the U.S.," which can be found by clicking here.)
"I cried on Saturday morning for happiness," American economist Gary Yohe told ABC News.
Yohe, a member of the IPCC team that shared the Nobel Peace Prize in 2007, has long been a leading authority in the now fast-growing field of environmental economics
He said his life's work has essentially been about trying to help humanity get a handle on global warming.
"After what happened in Copenhagen on that Friday, and what Obama did -- risking himself like that -- I woke up on Saturday and just knew ... the train was finally leaving the station," Yohe said.
"How to get the train out of the station" is a phrase economists and policy makers have used for years when talking about the task of getting American and other major governments to make the big adjustments necessary to respond to dangerous global warming in a coordinated effort to cut emissions and reassign dollars to help people around the world deal with the warming that cannot be avoided.
"What I really loved was that the U.S. was now part of the solution, not part of the problem," Yohe said of his Saturday morning realizations.
He added that it might now appear to many people that China was still "part of the problem."
China has been widely reported to have stubbornly, and at times even fiercely, resisted requests by other countries at the summit to compromise on matters of transparency about their emissions policies, and on other matters.
"The Chinese fought tooth and nail," against unambiguous language about considering 1.5 degrees Celsius (above pre-industrial temperatures) according to another official who had been in the room and who also requested anonymity.
Why, we asked.
"One reason," this official told ABCNews, "is that the Chinese have done their own climate studies and concluded that they cannot do better than 2 degrees Celsius above pre-industrial levels."
Yohe, on hearing of this, told ABC, "And, to spin that another way -- you've got to give credit to the Chinese, perhaps, for not wanting to promise something they don't think they can deliver."
Yohe's tears of happiness were matched by the beaming smile on the face of Columbia University agronomist Cynthia Rosenzweig at the baggage carrousel after the plane from Copenhagen had landed back in the United States.
Recognizing this reporter, for whom she had previously done an interview on the affects of global warming, Rosenzweig came up and said, "Isn't it great? I may be in a minority, but I feel.... Here we go! It's been exactly 25 years since I published my first paper on how global warming was going to alter wheat production in north America."