Bloomberg Philanthropies today announced the winners in its 2014 Mayors Challenge, an ideas competition that encourages cities to generate innovative ideas that solve major challenges and improve city life and that have the potential to spread to other cities…

Stockholm, Sweden: Biochar – for a Better City Ecosystem
Stockholm, like many global cities, is confronting the effects of climate change. Stockholm will create a citywide program that activates citizens as front-line change agents to curb this escalating problem. Together, the city and its residents will produce biochar, an organic substance that increases tree growth, sequesters carbon, and purifies storm water runoff. Citizens will bring their green waste to locations across the city for conversion to biochar and, ultimately, redistribution.