The authors are grateful for the support provided by the National Key Technology R&D Program from Ministry of Science and Technology of Grant NO. 2012BAC20B07. We acknowledge the support of the National Key Technology R&D Program and the Institute for Energy, Environment, and Economy at Tsinghua University, which is supporting Tianyu Qi’s doctoral research as a visiting scholar at the Massachusetts Institute of Technology. We acknowledge the support of ENI, ICF and Shell, initial Founding sponsors of the China Energy and Climate Project. This consortium of sponsors has provided support for researchers in the MIT Joint Program to engage in a five-year program of research focused on China. None of the sponsoring organizations played a role in the study design, collection, analysis, or interpretation of the data used for this study, nor did they influence our decisions to submit the article for publication, and all errors are our own.