Three global leaders coming together to deal with climate change was the headline grabbing moment for the recent C40 summit in Sao Paulo (read A tale of three men and 40 cities). Away from the cameras and sound bites was a field trip to Heliopolis, one of Sao Paulo’s biggest slums to drive home the messages that were being discussed in the conference.

As our bus convoy reached the construction site of Heliopolis, we saw round buildings resembling refinery towers. These were brand new apartment buildings for hundreds of Sao Paulo residents who currently live in the Heliopolis slum without proper access to basic services.

And while the round design of the buildings was eye-catching, the real catch is the way this project is being financed: A good portion of the finance comes from carbon finance credits that the city gets through a waste recycling project called Bandeirantes Landfill Gas to Energy Project (BLFGE) in which the methane of biomass waste (which accounts for 60% of Brazilian waste) is converted into energy. This way of generating energy qualifies for carbon credits.