Here is a selection of quotes from the leaders' gathering, which kicks off the UN conference in Glasgow:

Antonio Guterres

"It's time to say: enough," the UN Secretary-General said.

"Enough of brutalising biodiversity. Enough of killing ourselves with carbon. Enough of treating nature like a toilet. Enough of burning and drilling and mining our way deeper. We are digging our own graves."

He urged the delegates to: "Choose ambition. Choose solidarity. Choose to safeguard our future and save humanity."

Joe Biden

The US leader told the summit that he was sorry for his predecessor Donald Trump's decision to withdraw from the Paris Agreement.

"I guess I shouldn't apologize but I do apologize for the fact that the United States in the last administration pulled out of the Paris Accords and put us sort of behind the eight ball a little bit," he said, noting that one of his first actions on taking office this January was to re-enter the accord.

"The United States is not only back at the table but hopefully leading by the power of example. I know that hasn't been the case and that's why my administration is working overtime," he said.

Boris Johnson

The British Prime Minister warned delegates of "uncontainable" public anger if the conference fails and said future generations "will not forgive us".

"They will know that Glasgow was the historic turning point when history failed to turn," he said.

"They will judge us with bitterness and with a resentment that eclipses any of the climate activists of today -- and they will be right."

Mia Mottley

The Barbados Prime Minister said failure to provide nations with the funds to protect themselves and adapt to climate change was "measured in lives and livelihoods in our communities".

"That my friends is immoral and it is unjust," she said.

"We want to exist in a hundred years from now. And if our existence is to mean anything, then we must act in the interest of all our people who are depending on us."

Greta Thunberg

The climate crusader poured cold water on the summit.

"Inside COP there are just politicians and people in power pretending to take our future seriously, pretending to take the present seriously of the people who are being affected already today by the climate crisis.

"Change is not going to come from inside there, that is not leadership," she said at a nearby protest.

Mario Draghi

The Italian prime minister, who has just hosted G20 leaders in Rome, said COP26 "must now go further" than that summit.

"COP26 must be the start of a new momentum, a quantum leap in our fight against climate change," he said.

Emmanuel Macron

France's president urged the "largest emitters" to use the two-week event to accelerate their carbon cutting plans.

"The key over the next 15 days at this COP, is that the largest emitters whose national strategies do not align with our objective of 1.5C of warming, to raise their ambition... that's the only way of making our strategy credible again," he said.

Prince Charles

"We need a vast military-style campaign to marshal the strength of the global private sector. With trillions at its disposal," the heir to the British throne said.

Sir David Attenborough

"Perhaps the fact that the people most affected by climate change are no longer some imaginary future generations but young people alive today... perhaps that will give us the impetus we need to rewrite our story, to turn this tragedy into a triumph."