UNITED NATIONS (AP) — Former New York Mayor Michael Bloomberg, in his new U.N. job, said Tuesday that cities hold the key to confronting climate change because they account for 75 percent of the heat-trapping gases and their mayors have executive powers to reduce emissions.

The three-term mayor and billionaire businessman was a keynote speaker at the opening of a three-day U.N. meeting on making urban areas — where about 70 percent of the world’s population is expected to live by 2050 — more livable, sustainable, economically successful and environmentally friendly.