Hundreds of thousands of protestors marched through cities around the world on Sunday, demanding that world leaders act immediately against climate change.
Shattering the expected turnout of 100,000, an estimated 400,000 people processed through Manhattan alone – joined by UN Secretary Ban Ki-Moon, Leonardo DiCaprio and Al Gore.
In total, more than 2,000 marches took place in 168 counties around the world, ahead of this week's climate summit in New York.
The New York rally has been described as the largest mobilisation against climate change in history.
Speaking ahead of the march in London, actress Emma Thompson said: "This is important for every single person on the planet, which is why it has to be the greatest grass roots movement of all time.
"It's touch and go whether we're going to survive what we've done."
Thompson underlined the "vital importance" of a global climate deal to cut carbon emissions, adding: "This is the battle of our lives. We're fighting for our children."
In New York, Ban Ki-Moon wore a t-shirt proclaiming: "I'm for climate action" and told reporters: "This is the planet where our subsequent generations will live. There is no 'Plan B', because we do not have 'Planet B'."
Eddie Bautista, executive director of the New York City Environmental Justice Alliance, praised those who turned out to protest on Sunday. "We said it would take everyone to change everything – and everyone showed up," he said.
"Today, civil society acted at a scale that outdid even our own wildest expectations," Executive Director of 350.org, which organised the march, May Boeve, added in a statement.
"Tomorrow we expect our political leaders to do the same."
Ahead of the UN conference, which begins on Tuesday, faith leaders are meeting today in New York at the Inter-Faith Summit on Climate Change.
"We recognise that climate change stands today as a major obstacle to the eradication of poverty. Severe weather events exacerbate hunger, cause economic insecurity, force displacement and prevent sustainable development," a statement signed by 30 religious leaders says.
"The climate crisis is about the survival of humanity on planet earth, and action must reflect these facts with urgency."
Christian Aid's senior climate change advisor, Mohamed Adow, will be attending the UN summit as one of 38 NGO participants.
"Our leaders need to take this opportunity and respond to the call of the public to back up their positive words with firm actions to bring the misery of climate change to an end," he said.
"There is still time for us to change our course and put the world on a trajectory which will secure a safe and healthy future for us all. But we need to see political commitments this year.
"The People's Climate March shows that the time for action is now. This week world leaders have a chance to prove they can be trusted to do the right thing."