Xie, 74, served as China's top climate representative at 16 rounds of climate talks. His longstanding relationship with counterparts in the United States - including current incumbent John Kerry - has played a major role in securing global consensus on climate issues.
His resignation was announced following a video meeting with Kerry, and comes only weeks after he helped secure an agreement to tackle emissions from fossil fuels at the COP28 climate talks in Dubai.
Liu, 68, acted as Xie's special adviser in Dubai, and has long experience in climate diplomacy, participating in negotiations to draw up the 1997 Kyoto Protocol as well as the 2015 Paris Agreement.
Unlike Xie, Liu is a fluent English speaker. He served as under-secretary-general at the U.N. Department of Economic and Social Affairs (UN-DESA) from 2017 to 2022, with a broad brief that included climate issues.
