Former New York mayor Michael Bloomberg was appointed Friday to be the United Nations special envoy for cities and climate change, a position that will give the billionaire businessman and philanthropist an international stage to press for action to combat global warming.

Secretary general Ban Ki-moon chose Bloomberg, who made combating climate change a major focus of his 12 years as mayor and was very outspoken on how cities should be run to cope with ever increasing populations without harming the environment.

UN deputy spokesman Farhan Haq said Bloomberg will assist the UN chief in his consultations with mayors and other key parties “to raise political will and mobilize action among cities as part of his longer-term strategy to advance efforts on climate change”.

The secretary general also wants Bloomberg to bring “concrete solutions” to the climate summit he is hosting in New York on 23 September to try to galvanize action to combat climate change, Haq said.

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

He is scheduled to co-host the mayors’ summit of the C40 Cities Climate Leadership Group in Johannesburg next week.

The group is a network of large cities from around the world committed to taking measures locally that reduce climate-warming greenhouse gases and global climate risks.

At the summit, Bloomberg will hand over the chair and presidency of the group to Eduardo Paes, the mayor of Rio de Janeiro.

US Ambassador Samantha Power tweeted that “Mike Bloomberg knows how to get things done. We need more leaders like him here at the @UN.”

Last year, Bloomberg boasted that New York city’s air quality hit its highest levels in 50 years and now has the cleanest air of any major American city.

He said the level of sulfur dioxide in the air has gone down by 69 percent since 2008. The level of soot pollution has gone down by 23 percent since 2007 — achievements officials attributed to a combination of factors, including buildings burning lower-pollution heating oils or switching over to cleaner burning natural gas.