The flag named ‘We Are Watching’ is ten storeys high and made up of faces from 190 different countries.
It was created to put pressure on world leaders with the message that people are watching the decisions politicians are making in regards to the environment.
The flag has been in Doncaster for two days - from October 7 to 8.
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On October 8 a group of schools came together with Mayor Ros Jones, MP Ed Miliband, Cast Theatre, Phil Shepherd and the Hird Group to celebrate the flag's visit to Doncaster.
Ed Miliband, MP for Doncaster North, said: “We’re a long way away from where we need to be.
“It’s easy to say ‘we’ll do our bit’ but countries are not doing.
“The flag is brilliant - it shares an important message that we are watching.”
The MP was passionate about the role of young people in the conversation about climate change.
“I think the voice of young people is incredibly important,” he said.
“Young people are going to have to live with the climate emergency for longer than old people like me.
“Frankly, not enough has been done by generation and we do now need to act.”
He made reference to Greta Thunberg, a young climate activist who went on strike from school.
“If she can make a difference, one girl from Sweden then anyone can,” he said.
“It can be hard to feel like you can change the world but you can have an effect.
“Your voice is important - please use it.”
Pupils from McAuley Catholic School, the Communication Specialist College Doncaster and the Doncaster School for the Deaf were all in attendance.
Mayor Ros Jones, said: “Almost two years ago I declared a climate emergency in Doncaster.
“Since then Doncaster has suffered from significant flooding, heatwaves and freak weather events.
“We must act now - the planet is telling us to tackle this head on.
“We want to be carbon neutral here in Doncaster by 2040.
“We’re planting a million trees and creating green hearts all over the town.
“There has been significant conservation at the Hatfield Moors after the area was damaged by wildfire.
“We are working on making the council buildings energy efficient and replacing our cars with an electric fleet.
“But for us to continue we need significant government investment.
“Doncaster could become a national and international leader in green if we act now and play our part.”
Artist Dan Acher joined the event from Geneva via a video link.
He said: “The flag is made up of thousands and thousands of people from all over the world.
“The giant eye is watching the leaders in charge of the climate crisis.
“Raise your voices to protect our shared future on this planet.”
Micheal Hird from the Hird Group, said: “I’m sorry for what my generation has done to this planet.
“We need to work to leave the world in a better place for you.”
The Hird group is leading the way in recycled products in the rail industry.
They have so far turned 800 million plastic bottles into cable roughs and aviation tyres.