Boris Johnson has warned world leaders that they will be judged with “bitterness and resentment” by future generations if they fail to tackle global warming.

Around 120 heads of state and government are attending the world leaders’ summit at the start of the Cop26 talks, where countries are under pressure to increase action in the next decade to tackle dangerous warming.

There is also pressure on developed countries to deliver a long-promised 100 billion dollars a year – and more – in climate finance to help poorer nations develop cleanly and deal with the already inevitable impacts of a warming planet.

In a series of stark speeches, the leaders including US President Joe Biden, India’s Narendra Modi and German chancellor Angela Merkel, were urged to act for the sake of future generations.

UN Secretary-General Antonio Guterres told the Cop26 summit the world’s “addiction to fossil fuels is pushing humanity to the brink”.

Pointing to melting glaciers, relentless extreme weather events, sea level rise and overheating oceans, he warned: “We are digging our own graves”.

And he said while recent climate action announcements might give the impression the world was on track to turn things around, “this is an illusion”, and that failure to act would be a death sentence for vulnerable countries.

Joe Biden in Glasgow
US president Joe Biden arrives for the Cop26 summit (Adrian Dennis/PA)

He warned the “sirens are sounding”, and said: “Our planet is talking to us and telling us something. And so are people everywhere. Climate action tops the list of people’s concerns, across countries, age and gender.

“We must listen — and we must act — and we must choose wisely. On behalf of this and future generations, I urge you: Choose ambition. Choose solidarity. Choose to safeguard our future and save humanity.”

In his speech, the Prime Minister said the children who would judge today’s leaders are children not yet born, and their children.

“We are now coming centre stage before a vast and uncountable audience of posterity and we must not fluff our lines or miss our cue.

“Because if we fail, they will not forgive us – they will know that Glasgow was the historic turning point when history failed to turn.

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

Mr Johnson warned of the dangers of rising temperatures, jeopardising food supplies for hundreds of millions of people, more wildfires and eventually the loss of whole cities such as Miami, Alexandria and Shanghai.

“The longer we fail to act and the worse it gets and the higher the price when we are forced by catastrophe to act,” he said.

Global warming graphic
(PA Graphics)

Coining a phrase from activist Greta Thunberg, he warned that the promises to limit global temperature rises under the Paris Agreement would be “nothing but blah blah blah”.

And the anger and impatience of the world would be “uncontainable” unless Cop26 was the moment leaders got real about climate change, he said.

Channelling his hero Sir Winston Churchill, Mr Johnson said: “While Cop26 would not be the end of climate change, it can and it must mark the beginning of the end.”

Naturalist and broadcaster Sir David Attenborough warned humanity is “already in trouble” due to burning fossil fuels, destroying nature and releasing carbon into the atmosphere.

He said those who have done the least to cause the problem are being the hardest hit.

He asked: “Is this how our story is due to end – a tale of the smartest species doomed by that all too human characteristic of failing to see the bigger picture in pursuit of short-term goals?”

Boris Johnson, Antonion Guterres and Joe Biden
Boris Johnson and UN Secretary-General Antonio Guterres greet US pesident Joe Biden at the Cop26 summit (Alastair Grant/PA)

He added: “Perhaps the fact that the people affected by climate change are no longer some imagined 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.”

Addressing the opening ceremony, Barbadian Prime Minister Mia Mottley urged world leaders to “try harder” on climate change in a bid to avoid a “death sentence” for developing countries.

In a blistering speech, she pushed those in attendance, while launching a veiled attack at those who chose not to come to Glasgow for the key talks.

“We do not want that dreaded death sentence and we’ve come here today to say ‘try harder, try harder’.”

And the Prince of Wales urged the world to be on a “war-like footing” to tackle climate change, calling for a vast military-style campaign to marshal the strength of the global private sector and the trillions at its disposal to achieve the needed fundamental economic transition.