All over the world children and teenagers are walking out of their classrooms, because they're terrified that adults are sleepwalking towards climate breakdown.
I'm Matthew Green.
I'm a climate correspondent at Reuters and I've been following the story.
What was so extraordinary about the school strikes is that it started with a single pupil Gretta Thornburg in Sweden, standing on her own outside the Swedish parliament last August to protest the inaction over climate change.
Fast forward six months and you've got a million and a half kids all over the world who are delivering exactly the same message.
The children are paying more attention to scientists than than the politicians.
SOUNDBITE (English), GRETA THUNBERG, SAYING: "You say we're just children.
But we're only repeating the message of the united climate science." What I find remarkable about this story is this incredible non-linear change that we've seen.
Gretta Thurnberg launched her lonely protest outside the Swedish parliament.
Six months later you've got a million and a half school children and teenagers on the streets.
Now we know that non-linear change is precisely what climate scientists are afraid of it means feedback loops loops kick in and suddenly the climate system starts to break down much more quickly perhaps than than scientists anticipated even a few years ago.
But social change can also move incredibly fast as well.
Maybe this climate strike will go down as the moment where the human race started to turn around its greatest existential challenge.