In a bid to become more sustainable, Stockholm has found an unusual ally, old Christmas trees and other garden debris.
Produced via a special chemical process, biochar helps boost tree growth, improves soil quality and traps large amounts of carbon dioxide.
The Intergovernmental Panel on Climate Change highlighted biochar as a promising technology for keeping CO2 out of the atmosphere in its 2018 report.
When biochar is buried in the soil it acts as a carbon sink, storing CO2 for thousands of years.
Because biochar is incredibly porous, it can store large amounts of water.
We use the carbon to produce charcoal and put it back in the ground.
The project, which is still in the pilot phase, plans to provide renewable heating to up to 400 local homes.
Because of this potential to stimulate tree growth, biochar has even been involved in forest restoration studies.