U.N. Secretary-General António Guterres ratcheted up his warning about climate change and said the world’s thirst for fossil fuels is a “Frankenstein monster” that spares no one, while calling for greater attention to risks posed by artificial intelligence if its ascent goes ungoverned — even as some leaders played up its promise.

In 2017, weeks after Donald Trump’s first presidential election victory, Xi Jinping became the first Chinese head of state to address the World Economic Forum in Davos, Switzerland — winning applause as he inveighed against protectionism and declared that a trade war would hurt both sides.