Anxious about their future on a hotter planet and angry at world leaders for failing to arrest the crisis, masses of young people poured into the streets on every continent on Friday for a day of global climate protests. Organizers estimated the turnout to be around 4 million in thousands of cities and towns worldwide.

It was the first time that children and young people had demonstrated to demand climate action in so many places and in such numbers around the world.

They turned out in force in Berlin, where police estimated 100,000 participants, with similar numbers in Melbourne, Australia, and in London. In New York City, the mayor’s office estimated that 60,000 people marched through the streets of Lower Manhattan, while organizers put the total at 250,000. By the dozens in some places, and by the tens of thousands in others, young people demonstrated in cities like Manila; Kampala, Uganda, and Rio de Janeiro. A group of scientists rallied in Antarctica. “You had a future, and so should we,” demonstrators chanted in New York City.

Then, “We vote next.”

Banners in Kenya’s capital, Nairobi, ranged from ­serious to humorous. One read, “Climate Emergency Now.” Another said, “This planet is getting hotter than my imaginary boyfriend.”

In Mumbai, children in oversize raincoats marched in the rain. A sign in Berlin declared “Stop the Global Pyromania.”

“Right now we are the ones who are making a difference. If no one else will take action, then we will,” Greta Thunberg, the 16-year-old Swedish climate activist whose one-person strikes in Stockholm helped ignite a global movement, told demonstrators in New York City. “We demand a safe future. Is that really too much to ask?”

Whether this global action solves the problem that the protesters have identified — arresting greenhouse gas emissions to stave off a climate catastrophe — now depends on how effectively climate advocates can turn Friday’s momentum into sustained political pressure on governments and companies that produce those emissions.

Nowhere is that more true than in the U.S., which has produced more emissions than any country since the start of the industrial age, and which is now rolling back a suite of environmental regulations under President Donald Trump.

Organizers said there were demonstrations in all 50 states.

“In no way is today the end goal but is only a catalyst for future mobilization,” said Azalea Danes, 16, a high school student in New York City. “We will continue to strike.”

The protests were also notable for where they didn’t take place: China, the biggest greenhouse gas emitter of all.

While it was impossible to determine exactly how many people protested worldwide, a preliminary analysis by the Times found several cities had turnouts in the range of 100,000 and many more in the tens of thousands.

Rarely, if ever, has the modern world witnessed a youth movement so large and wide, spanning across societies rich and poor, tied together by a common if inchoate sense of rage. “They are mobilized around an issue of consistent concern across countries and across geographic areas,” said Dana Fisher, a University of Maryland sociologist who studies social movements. “It spans the developing-developed country divide. There aren’t that many issues that would unify in such a manner. And we all know the burden of climate change will fall on these kids’ shoulders when they are adults. They are acutely aware as well.”

The day began in the Asia-Pacific region. More than 100,000 protested in Melbourne in what organizers said was the largest climate action in Australia’s history. The rally shut down key public transport corridors for hours.

“Adults are, like, ‘Respect your elders.’ And we’re, like, ‘Respect our futures,’ ” said Jemima Grimmer, 13, in Sydney. “You know, it’s a two-way street, respect, and I’m angry that I have to be here.”

In Quezon City, in the Philippines, protesters, including one dressed as the Pokémon character Pikachu, held a sign that read: “Dead Planet Soon. Act Now!”

Thousands turned out in Warsaw, the capital of coal-reliant Poland. And roughly 100,000 demonstrators gathered around the Brandenburg Gate in Berlin.

In the Afghan capital, Kabul, where people are dying every day in horrific bomb attacks, young people took part in the global climate strike.

Across Britain, there were protests from Brighton to Edinburgh. The turnout in London was large, with organizers estimating more than 100,000 participants.

Theo Parkinson-Pride, 12, was passing by the Palace of Westminster with his mother, Catherine, 45, who said she had e-mailed her son’s school to tell them he would be missing classes on Friday. “I said to my mum, I feel this is more important than school today because soon there may be no school to go to,” Theo said.

Many websites went dark in solidarity with the protests or posted statements of support.

At the Seattle headquarters of Amazon, hundreds of employees walked out, continuing pressure on company leaders to do more about climate change. Those workers won concessions this week, as Amazon vowed to be carbon neutral by 2040 and to order 100,000 electric ­delivery trucks.