Space-based observations of megacity carbon dioxide

Urban areas now house more than half the world's population, and are estimated to contribute over 70% of global energy-related CO2 emissions. Many cities have emission reduction policies in place, but lack objective, observationbased methods for verifying their outcomes. Here we demonstrate the potential of satellite-borne instruments to provide accurate global monitoring of megacity CO2 emissions using GOSAT observations of column averaged CO2 dry air mole fraction (X-CO2) collected over Los Angeles and Mumbai. By differencing observations over the megacity with those in nearby background, we observe robust, statistically significant X-CO2 enhancements of 3.2 +/- 1.5 ppm for Los Angeles and 2.4 +/- 1.2 ppm for Mumbai, and find these enhancements can be exploited to track anthropogenic emission trends over time. We estimate that X-CO2 changes as small as 0.7 ppm in Los Angeles, corresponding to a 22% change in emissions, could be detected with GOSAT at the 95% confidence level. Citation: Kort, E. A., C. Frankenberg, C. E. Miller, and T. Oda (2012), Space-based observations of megacity carbon dioxide, Geophys. Res. Lett., 39, L17806, doi:10.1029/2012GL052738.