From London to New York City and from Perth to Paris, climate activists are taking part in a global general strike on Friday in what is expected to be the biggest day of climate demonstrations in the planet's history.
Some of the first protests were held in Australia and organizers have said "well over" 300,000 people gathered at more than 100 cities and towns across the country. Melbourne hosted the biggest march, according to organizers, with 100,000 people turning out, while 80,000 rallied in Sydney and 30,000 in Brisbane.
Thunberg tweeted: "Incredible pictures as Australia's gathering for the #climatestrike ... Australia is setting the standard!"
According to Swedish schoolgirl Thunberg, who is in New York ahead of the United Nations Climate Action Summit on September 23, around 4,638 events have been organized in 139 countries.
It is not just young people taking part this month, with labor and humanitarian groups, environmental organizations and employees of some of the world's biggest brands also set to participate.
By going on strike on September 20 -- and September 27 in a few countries -- protestors hope to put pressure on politicians and policy makers to act on climate issues.
In an opinion piece for CNN, teenager Katie Eder, co-founder and executive director for Future Coalition, said climate change was "the five-alarm fire that America's political leaders pretend not to see."
The 19-year-old added: "On Friday, we're striking for a Green New Deal; for the immediate cessation of fossil-fuel projects on sovereign indigenous land; for environmental justice; for the protection and restoration of nature; and for sustainable agriculture.
"We're striking for ourselves, for our friends and family, for the kid who lives down the street from us. We're striking because it's what we have to do."
Amazon & Microsoft workers striking
In March, over 1.6 million people took part in the first Global Climate Strike to demand transformative action on the climate crisis.
The global youth movement has asked for adults to join them this time and many have said they will respond.
Nearly 1,000 Amazon employees have pledged to walk out and Microsoft workers have also said they will join the strikes.
Microsoft Workers 4 Good tweeted earlier this month: "Microsoft workers will be joining millions of people around the world by participating in the youth-led Global Climate strike on September 20th to demand an end to the age of fossil fuels."
Outdoor clothing brand Patagonia has said it plans to shut down its operations on Friday to allow employees to join the Global Climate Strike. (Stores in Italy and the Netherlands will close on September 27, and in Switzerland on September 28.)
NYC gives 1.1 million students permission to skip school
In New York City 1.1 million pupils will be allowed to skip school on Friday after the city announced it would not penalize public school students joining the strikes, but made it clear that the students did need parental consent.
New York Mayor Bill de Blasio tweeted he supported the move: "New York City stands with our young people. They're our conscience."
Crowds will rally in downtown Manhattan at 12 p.m. ET, where a roster of young climate activists will speak, including Thunberg, who sailed to New York to attend the UN Climate Action Summit.
Thunberg the figurehead
It took Thunberg 15 days to sail across the Atlantic -- from Plymouth, UK, to New York City. She traveled on a on a zero-emission sailboat to reduce the environmental impact of her journey, according to a statement from her team.
The teenager, who last August began staging weekly solo protests outside the Swedish parliament every Friday, has become the figurehead of a burgeoning movement of youth climate activists.
This week she met former US President Barack Obama and told US politicians that they were not doing enough to combat climate change.
She has been invited to talk at the UN summit by UN Secretary-General Antonio Gutteres, who has called for heads of government to not bring speeches but plans on what he has called a climate emergency.
According to the Financial Times, leading economies such as Australia and Japan will not be invited to speak at the summit because of their continued support for coal is at odds with Gutteres' aims.
The Paris treaty, signed in 2015 by 195 nations, obliged governments to limit global temperature rises to "well below" 2 degrees Celsius and to strive for 1.5 degrees Celsius. The United States withdrew from the treaty in 2017.
In 2017, Obama lamented President Donald Trump's decision, saying in a statement that the deal was intended to "protect the world we leave to our children."