By Brady Dennis for The Washington Post

Ban Ki-moon, the globetrotting secretary-general of the United Nations, sat inside the Mayflower Hotel in Washington on a rainy morning this week, sounding relaxed and reflective.

One floor below, the ballrooms were bustling with business leaders, academics and government officials, who had gathered for a Climate Action 2016 summit. Their goal: Figuring out how countries can live up to the landmark climate agreement negotiated in December in Paris by hastening changes in the ways they produce and consume energy.

The rare accord calls on all nations — rich and poor — to increasingly limit emissions of carbon dioxide and other greenhouse gases over time, with the goal of staving off the worst consequences of global warming. The agreement, officially signed by 175 countries last month at the United Nations in New York, was the very definition of a worldwide collaboration. But it might not have happened — or come to fruition when it did — without Ban’s nearly decade-long persistence.