Photo from Greta Thunberg's 2018 climate strike shows massive growth over a year

On the left, on Aug. 2018, 15-year-old Greta Thunberg holds a climate strike with a sign reading "School strike for the climate" outside the Swedish parliament. Only a few other students joined her.

Driving the news: At right, Greta Thunberg, now 16, speaks to a huge crowd in Manhattan on Friday as millions of young people flooded streets around the world to demand political leaders take urgent steps to stop climate change. New York City announced its 1.1 million students were allowed to skip school to participate.

The impact: New York City officials said an estimated 60,000 people marched through the city on Friday, as adults swelled the ranks of students.

• In Melbourne, Australia, organizers said around 300,000 Australians joined rallies across the nation.
• In the United Kingdom, around 100,000 people attended a rally in central London, while more than 20,000 marched in Edinburgh and approximately 10,000 met in Brighton, organizers estimated.

Flashback: In March, Thunberg led the largest and most widespread demonstration on climate change since the run-up to the Paris climate summit in 2014 and 2015. Students in at least 112 countries participated.

“I believe that once we start behaving as if we were in an existential crisis, then we can avoid a climate and ecological breakdown. But the opportunity to do so will not last for long. We have to start today.”

Go deeper:

• In photos: Youth climate protests take over the world
• Watch Greta Thunberg's speech at the European Parliament in April