Tears flow often -- blood has once -- as climate negotiators from 195 nations gather every year in a different corner of the world for a physical and emotional endurance race.
Nerves are known to fray as the delegates' high-stakes mission to save humanity clashes head-on with the intransigence that comes from their other mandate to defend narrow national interests.
"There's tears at a lot of these meetings," said observer Alden Meyer -- a veteran survivor of the talks known for running deep, deep into extra time as negotiators cling onto their bargaining chips as long as they can.
"Sometimes they're tears of frustration and anger, sometimes they're tears of joy," the Union of Concerned Scientists analyst told AFP at the latest round of talks, in Paris, meant to finally yield a universal climate rescue pact.
This year marks two decades since the first Conference of Parties (COP 1 to insiders) gathered under the UN's climate convention in Berlin in 1995.
The annual meetings generally aim to close on a Friday, but often spill over into Saturday, sometimes even Sunday.
By this time, bleary-eyed delegates, observers and journalists are to be found wandering the corridors like zombies, desperate for sleep and much in need of a shower, vying for an empty couch or beanbag to catch forty winks.
- 'Hellish' -
"The sleeplessness, it gets to you after two or three nights. You're sort of operating on fumes, you're not thinking straight, you've got a headache, you forget what day it is," said Meyer.
The very nature of the process is what results in these poker-like standoffs.
There is no vote, and decisions are approved with a bang of the gavel on "consensus" -- a fuzzy term which itself has caused a lot of conflict, but basically means no lone voice is loud enough to stop a deal if there is overwhelming support.
The late nights and constant bickering can take their toll.
At COP 13 in Bali, then-UN climate chief Yvo de Boer was reduced to tears in front of thousands of delegates and had to be led off stage as the United States sought to block an agreement.
Two years later in Copenhagen, Venezuelan negotiator Claudia Salerno stole the limelight when she waved a red-stained palm and claimed that developing countries were reduced to "cutting our hands and drawing blood" to get a speaking turn.
"The final hours of any COP are hellish," said Mohamed Adow of Christian Aid, which pushes poor country interests at the talks.
He has attended six of them.
"Emotions run high because we're dealing with decisions which could mean life and death for millions of people.
"Added to that, the negotiations become very complicated at that stage just when people stop getting any sleep and the food begins to run out."
- 'I had to sleep' -
Tasneem Essop of environment lobby group WWF recalls the 2011 Durban COP -- which holds the unenviable distinction of having the longest overrun yet: two full nights.
By the time the conference held its closing session on the Sunday, with negotiators still bickering, "basically, I had to sleep".
"So we were sleeping... in the back of the plenary (hall)... lying on the floor. And then you have the occasional applause and you'll wake up to see if something's happened, and if something's not happened, you doze off again."
Like many others, Meyer comes prepared.
"I always have my eyepatch and earplugs and little circular pillow."
Copenhagen was the COP that failed to deliver the first truly universal pact to stave off worst-case-scenario global warming by curbing reliance on greenhouse gas-emitting coal, oil and gas.
Paris aims to not repeat history, and the French presidency of the talks has so far succeeded in holding negotiators to midway deadlines.
"It's quite eery, I must tell you," said Essop. "It never happens."
Bets are being placed on just how long this round will run, even as one high-level negotiator has divined that "pigs will fly" before a COP finishes on time.
"What's tough is trying to predict when it is going to end," said Adow. "Making the call whether to go home to bed or stay up in case it finishes abruptly in the middle of the night.
"As the stakes increase in the last hours and the countries step up their game, I expect the usual high-octane drama."
