Mayor Bill de Blasio announced an interim goal to reduce carbon emissions in New York City's environmental plan during a climate change conference Tuesday in Vatican City.

The city aims to reduce its emissions levels by 40 percent by the year 2030 -- a stop on its way to its grand goal to cut them by 80 percent by 2050, de Blasio told a global gathering of mayors and governors at Pope Francis' "Modern Slavery and Climate Change" event.

"Any city, any nation, any corporation not straining to reduce emissions simply isn't doing enough," the mayor said, according to a transcript released by his press office.

Climate change became "personal" to New Yorkers after superstorm Sandy struck in 2012 and killed 44 people in New York City, de Blasio said.

He was among the leaders who signed a document pledging action and stating that a December United Nations summit in Paris on global warming must be used to tackle human-induced climate change.

Pope Francis told the crowd the summit would address how global warming has forced people from impoverished regions, with migrants becoming susceptible to human trafficking.

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De Blasio in his speech noted that another attendee -- California Gov. Jerry Brown -- had set the "40 by 30" goal for his state.

He told reporters afterward that he hopes New York's business community will cooperate in meeting the goal, but, "If we see a lack of commitment, we'll mandate it."

He said Francis represents the "strongest moral voice in the globe" calling people to action on climate change.

De Blasio announced the city's "80 by 50" goal to reduce carbon emissions at last September's United Nations climate summit and said Tuesday that New York is the largest city in the world to make the commitment.