UNITED NATIONS  — Former New York Mayor Michael Bloomberg, who just joined the crowded race for the Democratic presidential nomination, has resigned his post as the United Nations special envoy for climate action.

U.N. spokesman Stephane Dujarric said Monday that Bloomberg sent a letter to Secretary-General Antonio Guterres on Nov. 11 saying he was stepping down from the U.N. post.

A longtime climate activist, the billionaire media mogul was initially appointed U.N. special envoy on cities and climate change by then-U.N. chief Ban Ki-moon in January 2014. Guterres gave him the new title in March 2018.

Dujarric said Bloomberg “was a catalyst in his role as a U.N. envoy to bring cities together … to mobilize in the fight against climate change.”

In Bloomberg’s resignation letter sent on Nov. 11, two weeks before he officially announced he was running for the Democratic nomination, the three-time mayor “thanked the secretary-general for his leadership on climate in the letter,” Dujarric said.

When Bloomberg was appointed to his last U.N. post in March 2018, he said that President Trump could become “a great leader” if he changed his mind about global warming and kept the United States in the 2015 Paris climate agreement. But that hasn’t happened.

Trump announced in June 2017 that he was withdrawing the U.S. from the Paris agreement, fulfilling a campaign pledge to quit the world’s chief effort to slow planetary warming.

Under the terms of Paris agreement, signed by former U.S. president Barack Obama, no country could pull out in the first three years after the Nov. 4, 2016, ratification.

U.S. Secretary of State Mike Pompeo submitted a formal notice to the United Nations starting the withdrawal process on Nov. 4. The U.S. withdrawal doesn’t become complete until the day after the 2020 election.

Pompeo’s statement touted America’s carbon pollution cuts and called the Paris deal an “unfair economic burden” to the U.S. economy.

In April, Bloomberg donated $5.5 million to the U.N. Climate Change Secretariat to help fill the gap left by Trump’s announced withdrawal from the Paris accord to ensure that it can continue helping countries meet commitments under the climate deal. He donated $4.5 million in 2018.

“The United States made a promise to meet the goals outlined in the Paris Agreement – and if the federal government won’t hold up our end of the deal, then the American people must,” he said in April.

Bloomberg’s new campaign website says: “As president, he’ll rejoin the Paris Agreement, and fight for a cleaner, healthier planet.”