At least $100 million will be used to begin to retrofit city housing projects with energy-efficient upgrades, Mayor Bill de Blasio announced Thursday.

The New York City Housing Authority, using funds arranged through the Obama administration, expects the work to "dramatically" cut greenhouse gas emissions, generate tens of millions of dollars in cost savings and create more than 500 jobs, de Blasio said at an event at a housing project in Canarsie, Brooklyn.

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"Global warming is changing our lives. Climate change is changing our lives. It's creating new challenges. We have to get ahead of it," de Blasio said.

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De Blasio, who called the program the largest energy savings effort of any public housing authority in the United States, is aiming to reduce emissions by 80 percent by 2050.

Julián Castro, the federal housing secretary, said the program would be used as a nationwide model.

"That's huge. Very significant," he said. "As former Mayor Ed Koch famously said, 'New York is where the future comes to audition.' "