Millions of people around the world held a global climate strike on Friday, inspired by activist Greta Thunberg.
Protesters across continents waved placards and chanted slogans in what could be the biggest ever demonstration over global warming caused by humans.
"Our house is on fire", Ms Thunberg said at a rally. "We will not just stand aside and watch."
The day began in the Pacific and Asia and culminated in a massive demonstration in New York.
It comes ahead of a UN summit next week at the organisation's headquarters in Manhattan. Activists are demanding greater efforts be made at the meeting to tackle climate change.
Ms Thunberg first started skipping school to protest against inaction on climate change in 2018.
Her actions have inspired schoolchildren and adults around the world to take up the fight.
What happened on Friday?
Pacific island nations like Kiribati, the Solomon Islands and Vanuatu - all threatened by rising sea levels - kicked off the strike. Posts online showed citizens chanting: "We are not sinking, we are fighting."
What did Greta Thunberg say?
The teenage activist was greeted like a rockstar at the rally on Friday, with chants of "Greta! Greta!" resounding around New York's Battery Park.
"This is the biggest climate strike ever in history, and we all should be so proud of ourselves because we have done this together," the teenager told demonstrators.
Ms Thunberg said about four million people took part in the strike around the world, "and we're still counting."
"This is an emergency. Our house is on fire. And it's not just the young people's house, we all live here - it affects all of us," she told the crowd.