At about 2pm, they started to stream down corridors and sift down escalators, weaving through the halls leading to the negotiating rooms and out through the main security gate - hundreds of them.
The United Nations climate change talks had not been going well - perhaps an understatement - and for the first time in the 18-year history of these negotiations, the environment groups and civil society organisations had had enough.
It was time to walk out of Poland's national sports stadium in Warsaw - groups from all corners of the world donning white t-shirts and streaming out of the talks, known as COP19, beneath a giant United Nations sign reading “Welcome”.
Speaking exclusively to DeSmogBlog outside the talks after checking in his UNFCCC badge, Kumi Naidoo, the human rights activist and executive director of Greenpeace International, insisted the walkout was not a sign of them giving up.
“It is clear that what's happening here is not just betrayal to future generations - because it is clear that the people negotiating here are not going to bear the brunt of climate impacts. It's our children and grandchildren that are going to.
“This is not about giving up, but is about taking the struggle to a different level. If we are to get a solution out of this COP we need people around the world to start - in every country - putting pressure on their governments to actually come to these COPs with a very strong mandate which has serious levels of ambition with regards to cutting carbon.
“Serious ambition too with regard to ensuring that poor countries have the money to adapt to climate change and not follow the same dirty energy pathway that rich countries followed to build their economies.”