Classrooms in capitals from Bangkok to Berlin, Lagos to London emptied as ambitious organizers of the student strike hoped to stage 1,000 demos in more than 100 countries.
As youngsters hit the streets in cities across the globe, nations meeting at the UN environment assembly in the Kenyan capital Nairobi announced that they had agreed to “significantly reduce” single-use plastics over the next decade.
But experts said the pledge – which only referred to man-made global warming and made no mention of the fossil fuels driving it – fell far short of the steps needed to tackling Earth's burgeoning pollution crisis.
As the marathon talks drew to a close, students flooded into the streets across Europe and Asia carrying placards reading: “There is no planet B”, “You're destroying our future” and “IF you don't act like adults, we will”.
Despite three decades of warnings, carbon dioxide emissions hit record levels in 2017 and again last year.
Loading the atmosphere with greenhouse gases at current rates will eventually lead to an uninhabitable planet, scientists say.
In Stockholm, Swedish teen activist Greta Thunberg who inspired the protests, was thronged by journalists and several dozen protesters, one carrying a banner declaring “Make the Climate Greta Again”.
“We are living through an existential crisis that has been ignored for decades and if we do not act now it may be too late,” the 16-year-old told Swedish public television station SVT.
Thunberg has been nominated for the Nobel Peace Prize for her activism.
In Delhi, one of the world's most polluted cities, 200 students took part in a colourful protest, waving ribbons, juggling and performing stunts with hoops.
“We have to make a choice whether we want to sit and be indifferent or do something for our planet,” said 16-year-old student Srijani Datta.
“Most of us are 16-17 and we're going to turn 18 soon… As voters we will show we care about climate change. If you can't give us that, you will not get our votes.”
Young climate campaigners in India. Photo: AP Photo/Altaf Qadri
In Sydney, 18-year-old Charles Rickwood warned that Australia's famous Great Barrier Reef could be destroyed.
“Especially if current trends in the environment continue, we'll see the one, two degrees increase in our ocean then it will simply become unsustainable and we could lose the entire Great Barrier Reef,” he told AFP.
'Let us breathe!'
European students were also out en masse, with several thousand youngsters thronging the streets of central London in a raucous demonstration featuring a multitude of banners, placards and sloganeering.
Packing into Parliament Square, they cheered and chanted “Change… now!” before marching past Downing Street and massing outside Buckingham Palace.
“They're not going to stop me trying to save the planet,” said 15-year-old Joe Crabtree, from southwest London who had missed two exams to join the demo.
But there were even younger protesters too, with eight-year-old Max Bazargan wearing a gas mask and waving a banner reading: “Stop the greed, let us breathe.”
At one point, a group of children climbed the huge Queen Victoria memorial in front of the gates of Buckingham Palace, while others clambered atop of London's famous red telephone boxes.
Elsewhere, around 2,000 young people marched through Warsaw where one banner said: “I hate climate change even more than school.” Similar numbers also gathered in central Prague.
In Madrid, some 4,500 young demonstrators hit the streets while another 2,000 gathered in Barcelona, police said.
“Not one degree more, not one species less,” they chanted, waving banners warning: “There is more plastic than common sense.”
“Our politicians appear to be signing more autographs than laws. They have to put the focus on the environment,” 19-year-old psychology student Rosalia Gonzalez told AFP.
“They say we're the future but young people are the present, if we don't act now, we never will.”
'They should be in school'
Thousands also marched through the streets of Berlin and Munich to denounce the lack of political action, waving slogans like: “I believe more in unicorns than in the will of politicians to save the planet” and “We will go to school if you keep the climate cool”.
But the global action drew a mixed reaction from politicans, with Germany's Economy Minister Peter Altmaier saying they should be in classes and Australia's Education Minister Dan Tehan saying that striking was “not something that we should encourage”.
But New Zealand Prime Minister Jacinda Ardern hailed the action, saying: “We hear you and we're getting on with setting a path for carbon neutrality.”
“Please keep bringing as many people as you can with you because we simply won't achieve our goals alone.”
Greenpeace praised the global protest, saying adults needed to learn a lesson or two.
“Imagine if their parents, grandparents, aunts and uncles – people with the power to vote for change – were to make the same kind of effort,” said John Sauven, head of Greenpeace UK.
“Grownups cheering on the school strikes are like footballers applauding the crowd. You're on the pitch. Score a goal, or at least assist.”
In the Indian Ocean island nation of Mauritius, students circulated a petition to be submitted to the government demanding concrete measures.
“The planet is heating up, the youth are rising up,” they chanted.
'My eyes hurt from pollution'
The Paris treaty calls for capping global warming at “well below” two degrees Celsius, but the planet is currently on track to heat up by double that figure.
The UN's climate science panel warned in October that only a wholesale transformation of the global economy and consumer habits could forestall a catastrophe.
“My eyes hurt from pollution. My shirt gets dirty from dust,” 13-year-old protester Shagun Kumari told AFP in Delhi.
“I want fresh air that won't harm my lungs and clean water to drink so that I don't keep falling sick.”
As fellow Indian protester Datta noted: “If the children and youth don't care then in a country like India, you can't make this happen.”