Last year a 15-year old girl in pigtails decided to walk out of her classroom and sit on the steps of Sweden's parliament every Friday with a homemade sign: "School Strike For Climate".
Since then, the Fridays for Future movement sparked by Greta Thunberg, now 16, has gone global.
In September, millions of young people on every continent poured into the street to demand action. Today they march in Madrid, where negotiators from nearly 200 nations at UN climate talks are feeling the heat of an increasingly angry and anxious world.
Some of these young activists spoke with AFP.
Arshak Makichyian, 25, graduated from the Moscow Conservatory in June a virtuoso violinist, but his career is on hold. When he returns to Moscow by train in mid-December, he will come before a judge to face charges, and likely punishment, for "organising an unauthorised strike" for climate.
"There is very little information in the Russian media about climate change, so I started reading about it in English and discovered how serious the problem is. That is also how I learned about Greta Thunberg."
"After the global student school strike in March, I began protesting alone in Pushkin Square - in Moscow it is the only way to protest legally without a permit, which was never granted in any case."
"Now I am not alone, there are students in seven or eight Russian cities striking every week. In Moscow, we do it in a queue - one person stands with a sign and then steps aside to let the next person in line do the same. If two people do it together, they can be arrested."
"For years I practised my instrument every day, but I have taken a break. It felt really strange to play the violin while the Titanic is sinking. Also, it's complicated getting a job with an orchestra if you have decided not to fly."
"I came to Madrid mainly to meet other Friday for Future activists from around the world."
When she realised that global warming is not just an environmental issue but a social one too, 18-year-old Nicole Becker, a first-year university student in Buenos Aires, switched from psychology to international law. Today, climate change is her top priority.
"I saw a video of Greta and asked myself: why are young people in Europe striking, while no one in Argentina is even talking about the problem?"
"I am in Madrid to represent Latin-American youth, and because it's where world leaders are deciding my future. I want them to hear me, I want to have a voice."
"There is a lot of poverty in Argentina, and it has a connection with climate change. When I understood that, and that my future is at risk, I knew I had to fight, and influence the decisions that my government makes. I dedicate my time to climate change now, also because I'm afraid."
"Those of us living in rich cities are not the ones most affected, so we have to care for those who are- this is a moral challenge. In Argentia, lots of people say, 'First we have to improve the economy, then we can worry about the environment'. They don't understand climate change is making their economic problems worse."
For Chloe McCann, an 18-year-old high school student in Tasmania, Australia, global warming is not an abstract concept. Several years ago, her family home was consumed by wildfires that have become more widespread and intense as global temperatures rise.
"Lots of people suffer from climate anxiety, and maybe I'm one of them. We hear all these negative things, and it gets you down. Sometimes it's hard to have hope. That's one reason I'm here - to learn about what I can do."
"We have a lot of bushfires, it's a huge thing in Australia right now. When I was younger, we were very unlucky and lost our home. This is still a trigger for me - I look back and think 'You know what, climate change makes fires worse'."
"Of course we have to make changes at a personal level - taking public transport, avoiding plastic, consuming less. If everyone does a little bit, it can make a big difference. But a lot of people feel they have to do everything, and then wind up doing nothing -- that's the worst."
Lea Ilardo, 21, of France has been living for the last year-and-a-half in Quebec, where she studies political science and environmental policy. "Sadly, I don't expect much to come out of this process," she says.
"Personally, I live a privileged life. I feel that my role is to fight on behalf of people whose voices have been muted, and who are focused on surviving. We live in a world fractured by inequality at every level - between generations, within and between countries."
"Greenhouse gas emissions just keep climbing -- they will hit record levels again in 2019. In the end, we have the impressions that our efforts don't really make a difference."
"It is terrifying to think that we don't know what world we will be living in a decade from now. This completely undermines our capacity to project ourselves into the future. How bad do things have to get before things really change? Is humanity really so blind?"
"The world built a multilateral regime to fight climate change. But it has been so ineffective that we have to ask the question: is it better to keep trying to change things from the inside, or do we become part of the problem just by being here?"
Fifteen-year-old Erik Christiansson from Utrecht, hair neatly parted on the side, speaks with clarity and confidence that belies his age.
"I have come to Madrid to let my voice as a climate striker be heard at the highest level, and to make sure that the parties to the COP are doing enough to combat climate change."
"Yes, I have adapted my lifestyle: I don't eat meat, I do not fly any more. But I don't think we should judge someone on the basis of their carbon footprint."
"Greta Thunberg is setting an example for lots of people around the world. She is one of the reasons I started doing climate strikes."
"If this process fails, I will continue to do actions in my country to pressure my government. I will attend the COP next year to ensure that - if it is not done here in Madrid - it will be done next year."
"Who's at fault? Of the companies responsible for the most CO2 emissions, the top 100 produce 70 percent. Oil and gas companies such as Saudi Aramco, BP and Shell are very high on the list. We should also hold accountable the governments that can stop this but are not doing so."
Shiina Tsuyuki, 18, attended a 'green' high school in Bali, Indonesia, and now she has gone back to Japan, where most people, she says, are barely aware that climate change is a problem.
"I'm gathering information at the climate COP to inform other Japanese youth. Japan is so organised that people don't really notice when the temperature goes up a little."
"But they noticed when the biggest typhoon in years hit my city of Yokohama. People have to realise that the size of the typhoon was not natural, that it was enhanced by climate change."
"All my friends in my university don't really care about the environment. They are not afraid at all. They have no information. Knowledge has to come before action."