Their final push took barely two weeks.
The "loss and damage" inflicted by climate-induced disasters was not even officially up for discussion when UN talks in Egypt began.
But a concerted effort among developing countries to make it the defining issue of the conference melted the resistance of wealthy polluters long fearful of open-ended liability, and gathered unstoppable momentum as the talks progressed.
In the end, a decision to create a loss and damage fund was the first item confirmed on Sunday morning after fraught negotiations went overnight with nations clashing over a range of issues around curbing planet-heating emissions.
"At the beginning of these talks loss and damage was not even on the agenda and now we are making history," said Mohamed Adow, executive director of Power Shift Africa.
"It just shows that this UN process can achieve results, and that the world can recognise the plight of the vulnerable must not be treated as a political football."
Loss and damage covers a broad sweep of climate impacts, from bridges and homes washed away in flash flooding, to the threatened disappearance of cultures and whole island nations to the creeping rise of sea levels.
Observers say that the failure of rich polluters both to curb emissions and to meet their promise of funding to help countries boost climate resilience means that losses and damages are inevitably growing as the planet warms.
Event attribution science now makes it possible to measure how much global warming increases the likelihood or intensity of an individual cyclone, heat wave, drought or heavy rain event.
This year, an onslaught of climate-induced disasters -- from catastrophic floods in Pakistan to severe drought-threatening famine in Somalia -- battered countries already struggling with the economic effects of the Covid-19 pandemic and soaring food and energy costs.
"Everyone also now realises that things have gone way beyond our control," said Harjeet Singh, head of global political strategy at Climate Action Network International.
Who pays?
The agreement was a high-wire balancing act, over seemingly unbridgeable differences.
On the one hand, the G77 and China bloc of 134 developing countries called for the immediate creation of a fund at COP27, with operational details to be agreed later.
Richer nations like the United States and European Union accepted that countries in the crosshairs of climate-driven disasters need money, but favoured a "mosaic" of funding arrangements.
They also wanted money to be focused on the most climate-vulnerable countries and for there to be a broader set of donors.
