We name name our most important sustainability agreements after cities, e.g. the Kyoto and Montreal Protocols, the Basel Convention, and most recently, the Paris Agreement. The world came together in Rio de Janeiro in 1992 finally cementing a comprehensive sustainability agreement that spawned the IPCC and Agenda 21s. Yet more than half the world’s GHG emissions were generated after the Rio convention. How will the talk of sustainability move to genuine action, and how might the world’s cities lead in this effort? Can they? Is there still time?