Even its most enthusiastic proponent, UK Prime Minister Boris Johnson Tuesday was only "cautiously optimistic" that change would come.
Johnson before the summit said that the climate crisis was like a soccer match in which the world was losing by 5 goals to 1.
By Tuesday, he said the scoreline was closer to 5-2 or 5-3 after big announcements on reducing methane emissions, ending deforestation, and pledged cash to tackle climate change. But losing by two points is still losing.
Countries have yet to commit to an agreement that would limit global temperature rises to 1.5 degrees Celsius above pre-industrial levels — a threshold identified as crucial by scientists in preventing irreversible damage to the planet.
Hopes of reaching such agreements, the only metric by which COP26 could really be seen as a triumph, receded fast.
China's President Xi Jinping was widely criticized for failing to attend the summit at all, given that China is responsible for nearly 30% of the world's carbon emissions — more than any other country.
Just as critical is China's reluctance to commit to the 1.5 degrees target. To reach that level, the nations of the world would need to reach net-zero carbon emissions by 2050, according to the UN Intergovernmental Panel on Climate Change.
Xi Zhenhuan, China's climate envoy, said China was "not against" the target but has also refused to commit to it. Without Chinese buy-in, 2 degrees is likely the best that can be achieved.
Meanwhile, India — the world's fourth-largest polluter, this week announced that it would seek carbon neutrality. The move has been widely hailed as a step in the right direction for a country that has not previously made a net-zero commitment.
But the fact remains it lags 20 years behind net-zero commitments made behind high-income countries including the US and the UK, and would set the world on a path to miss the 1.5-degree target.
Neither have high-income countries in the West lived up to their promises: A 2015 pledge from the Paris climate summit saw nations including the US and Germany pledge donations of $100 billion to poorer countries to help tackle climate change. That pledge remains unfulfilled.
The stakes of the Glasgow summit — dubbed "the last chance saloon" by Britain's Prince Charles — have been made clear. The UN warned that the consequences of failure are conflicts, mass migration of whole populations, greater terrorist threats and food insecurity.
The Prime Minister of Barbados Mia Mottley used a speech at COP26 on Tuesday to warn that a 2-degree rise would be a "death sentence" for islands and coastal communities like hers.
"If our existence is to mean anything, then we must act in the interest of all of our people who are dependent on us," she said.
"And if we don't, we will allow the path of greed and selfishness to sow the seeds of our common destruction."
Johnson and other world leaders departed Glasgow on Tuesday, leaving teams of negotiators trying to thrash out the terms of a deal that could have historic significance. The omens so far are not good.
