Diplomats say New York's former mayor Michael Bloomberg has been chosen by Secretary-General Ban Ki-moon to be a U.N. envoy for cities and climate change.

The diplomats spoke on condition of anonymity ahead of an official announcement which could come as early as Friday afternoon.

Bloomberg served three terms as New York's mayor before handing the reins of the America's largest city to Bill de Blasio on Jan. 1.

The billionaire businessman and philanthropist turned politician made combating climate change a major focus of his 12 years as mayor. He was also very outspoken on how cities should be run to cope with ever increasing populations.

Bloomberg is scheduled to co-host the Feb. 4-6 mayors summit of the C40 Cities Climate Leadership Group.