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Rio de Janeiro is considered one of the most vulnerable cities in Latin America when it comes to climate change.
Of course, it boasts pristine white beaches, and scenery to take the breath away of any visitor. But rising temperatures and sea levels mean this city in Brazil is on the brink of disaster.
Over the last 10 years, landslides have swept through the favelas folded into the city's hillsides.
The houses, constructed with corrugated iron and breeze blocks, don't stand a chance when faced with Mother Nature here.
On the banks of Guanabara Bay, I met biologist Mario Moscatelli.
He considers President Jair Bolsonaro's policies a disaster for the planet, and is on a one-man mission to confront global warming.
He said: "We have a strange president when the issue is the environment."
Walking through an arcade of young Mangrove trees, it's clear this is Mario's passion project, working to create the biggest urban mangrove forest in Brazil. So far, he's planted three quarters of a square mile, with his team planting more every day.
"This is one way to fight against climate change. These trees are very, very important."
He shows me seedlings planted on the edges of what was once one of Brazil's largest landfill sites - Jardim Gramacho - covering an area of 130 acres.
In the seventies and eighties, rubbish was dumped directly into the mangroves, suffocating the vegetation, and killing the area.
In 1997, Mario was called on to rescue the mangroves from near death. Since then, he's come some way to create a beacon of hope for Rio's forest regeneration.
Some way, in fact, that he's recovered an additional 130 acres surrounding the original landfill site.
But it's not straightforward - the disastrous habits of man are taking their toll. His biggest problem now is not the rubbish that is deposited here, but the excess that flows downstream from rivers.
So he and his team, picked from local communities, build a fort between the mangroves and the river - determined to keep the rubbish offensive out.
As he guided me further into the Mangroves, we see what Mario's dream is all about. Of course, this is just one project when confronted with vast areas of rainforest being destroyed as I write this.
But the seedlings planted here are planted by a man so desperate to change things here. At least some hope is taking root right now in Mario's mangrove.