Greta Thunberg told a huge crowd in Manhattan that she thought around four million people had taken part in Friday’s global climate strikes.
That is an extraordinary number, reflecting the urgency of this moment.
What was also extraordinary was the uniformity of the message being delivered to governments all over the world: do more, now.
But will they?
We may find out on Monday, where heads of state and government are converging in New York for the United Nations climate summit.
Leaders are being told by an increasingly impatient UN Secretary General that there is no room for fancy speeches and if they want time at the podium they must bring concrete plans and enhanced commitments to tackling the crisis.
We expect the UK to do so, perhaps alongside world polluter number one, China.
There may also be eye-catching commitments from big business about responsible investment and financing, finally, perhaps, pulling levers large enough to make a difference.
But will this day, historic in so many ways, be THE tipping point that pushes Donald Trump to declare that America, one of the world’s biggest polluters, will stay in the Paris Climate Agreement?
I doubt it.
With Mr Trump in office, coordinated national effort in the US is a lost cause.
The question is whether the rest of the world can combine to pick up the slack, do it quickly, and do it equitably, so that the poorest and most vulnerable in our world who bear the least blame for creating the climate crisis do not bear the most pain as we try to use the ever-narrowing window for action.
After the climate strikes, the leaders coming to New York should be in no doubt that the people demand this is exactly what happens.
If elected representatives start to believe that their own political futures are on the line if they do not respond, maybe we will see the great leap forward that is needed, with or without America’s help.
Author: Hannah Thomas-Peter