Kerry, 80, has been a fixture in the United States’ climate diplomacy for decades. As secretary of State during the Obama administration, he helped negotiate the Paris Climate Agreement in 2015, which established the framework in which countries agreed to set their own domestic targets for reducing greenhouse gas pollution. The agreement set a goal of keeping temperatures from climbing no more than 2 degrees Celsius above pre-industrial levels, as well as a more ambitious stretch target of 1.5 degrees.

He built a strong rapport with China’s lead climate negotiator, Xie Zhenhua, who is reportedly leaving his post as well. The relationship between the two veteran diplomats often yielded agreements between world’s top two greenhouse gas emitters to combat the pollution, even as they struggled to maintain momentum for tackling climate issues amid the rising tensions between Washington and Beijing.