Danish, U.N. and other national security forces were deployed in unprecedented numbers to Copenhagen and specifically to the Bella Center, where the two-week climate talks were due to end Friday. Among the leaders to be secured were such controversial figures as Venezuelan President Hugo Chavez and Zimbabwe's leader Robert Mugabe.
Nearly all of the 30,000 non-government organization and observer representatives were locked out from the building as of Thursday, with numerous side events canceled to prepare security for the high-level event with the world leaders.
A group of NGOs wrote an open letter to Yvo de Boer, the United Nation's top climate official, and conference President Lars Lokke Rasmussen saying it was "unacceptable that civil society observers should be limited in this forum."
Kumi Naidoo, head of Greenpeace International, said civil society participation "has been shrunk to an absolute minimum." He added the summit started off transparent but in the final days had been on a "slippery downward slope."
De Boer has since defended the move, saying it was a result of several disruptive events inside the Bella Center.
The events staged by climate activists inside the Bella center included "strange packages being found in different places," people disturbing group sessions and staging sit-ins, de Boer said. The disruptions were "beyond everything we have ever seen in this process," he said.
The Bella Center has been a madhouse for quite some time. The second week has seen journalists and NGOs arriving in Copenhagen in droves, with authorities unable to handle the crush.
The Bella Center can hold 15,000 people but nearly 45,000 people were registered for the event. Frank McDonald of The Irish Times fittingly described the venue as "bedlam," a hint to a psychiatric hospital in London notorious for its cruelty to patients.
NGO representatives and delegation members had to wait for hours in the cold to register.
John Sweeney, a member of the U.N. Intergovernmental Panel on Climate Change, which was awarded the Nobel Peace Prize in 2007 along with former U.S. Vice President Al Gore, waited eight hours in line only to be told the reception desk was closed. The next day, he again joined the queue and, after another six hours of waiting, finally got in.
Outside, demonstrators repeatedly clashed with police all over the city, with around 1,500 arrests made over the course of the conference.
Police action has been widely criticized; the Danish government had pushed through a bill allowing police to temporarily detain protesters for 12 hours without charges -- a move blasted by civil rights organizations.
On Saturday, when roughly 100,000 climate activists took the streets, police pre-emptively detained around 1,000 protesters and made them sit handcuffed on the icy ground for several hours. On Wednesday, a group of around 2,000 protesters marched toward the Bella Center to demand entry but they were stopped by Danish riot police wielding batons.
Notable deaths of 2014 [PHOTOS]