 As engines of economic opportunity and innovation, the unprecedented growth in global cities mean they also emit a growing share of global greenhouse gases and face a mounting health crisis driven by local air pollution. While a small subset of cities have responded to these challenges with renewed leadership and commitment, most are restrained by a lack of relevant quantitative information about their atmospheric emissions. The scientific community has made profound advances characterizing atmospheric pollution in new detail and greater accuracy from a combination of space and ground measurements and modeling systems. This new capability, however, remains disconnected from urban decision makers in desperate need of better information. I propose to close this gap between need and capability by building a global information network that leverages these new scientific capabilities in collaboration with a suite of pilot cities across five continents, transforming the ability of local actors to simultaneously tackle the dual crises of local health and global climate change.