The film highlights the importance of nature in tackling climate change, encouraging people to "protect, restore, fund" earth’s natural ecosystems.
“This is not a drill,” Ms Thunberg said in the film.
“We are living in the beginning of a mass extinction,
“Our climate is breaking down.
“Children like me are giving up their education to protest."
The 16-year-old added that up to 200 species are going extinct everyday, and forests are being cut down at a rate of 30 football pitches a minute.
“But we can still fix this. You can still fix this,” she said.
In the short film - directed by Tom Mustill - Mr Monbiot said trees and the natural ecosystems are the most effective way to reverse the effects of climate change
“Nature is a tool we can use to repair our broken climate," he said.
“Right now, when we need nature the most, we’re destroying it faster than ever.”
He added that humans must stop burning fossil fuels in order for nature to regenerate and restore the planet.
“These solutions could make a massive difference, but only if we leave fossil fuels in the ground as well,” said Mr Monbiot.
“We spend 1,000 times more on global fossil fuel subsidies than on nature-based solutions, said Ms Thunberg.
"This is your money, it is your taxes, and your savings,” she added.
The activist ended the video, stating: “Everything counts. What you do counts.”
Their call for action on the climate crisis comes as the largest climate protests in history are expected to take place across the world on Friday.
Students and young people are gearing up for the protests, with adults being encouraged to join the strikes for the first time.
The UK Student Climate Network (UKSCN) says more than 200 events are taking place across the UK.
Unions, charities, businesses and politicians have rallied behind the cause.
Labour leader Jeremy Corbyn, who will be addressing a rally of climate strikers outside Parliament on Friday, has taken to Twitter to back the children going on strike, saying they "are leading the way and I'll be proud to join them tomorrow".
Some businesses are actively supporting their workers to take action, with outdoor clothing company Patagonia closing stores and offices globally, and taking out ads to back the strikes.
The Co-operative Bank has teamed up with the Unite union to support its workforce to take part in the climate strikes around the country.
Co-operatives UK is backing young people "sounding the alarm to governments globally that 'business as usual' on climate change isn't good enough".
These protests will mark the UN Climate Summit on September 23, where Ms Thunberg is expected to give a speech.
In an Instagram post, she wrote: "Tomorrow we strike back!
"5225 events in 156 countries on all continents. Including Antarctica!
"And counting... Everyone is welcome.
"Everyone is needed."
Since she made global headlines campaigning outside Swedish parliament, Ms Thunberg has been the inspiration behind the movement to tackle climate change.
She is currently in the US, where she is currently rallying with young activists.