Paris Mayor Anne Hidalgo speaks at the opening ceremony of the 2018 Global Climate Action Summit (GCAS) held in San Francisco, U.S., Sept. 13, 2018. The Global Climate Action Summit, which brings delegates from city and regional governments, industries and research institutions to western U.S. city of San Francisco to enhance cooperation in tackling climate change, officially opened on Thursday. (Xinhua/Wu Xiaoling)