The city would have to raise an additional $5 billion.

Mr. Bloomberg said that the price tag was high, but that the cost of not taking action would be higher. Hurricane Sandy caused $19 billion in damage and loss of economic activity for the city, he said, and if a similar storm were to strike three decades from now, the cost could be $90 billion.

“This is a defining challenge of our future,” he said.

Mr. Bloomberg delivered the recommendations in an elaborate presentation, including a documentary-style video and a glossy report, that underscored how he is making climate change a signature issue toward the end of his tenure. In recent months, he has sought to contrast his activist stance on climate change with what he has said is the unwillingness of Washington to tackle these issues.

He chose to speak not at City Hall, but at the Brooklyn Navy Yard, which was damaged by four and a half feet of floodwater during the hurricane.

Mr. Bloomberg’s speech came a day after his aides released information on what they predicted would be the effect of climate change on the city.

Officials estimated that more than 800,000 city residents would live in the 100-year flood plain by the 2050s — more than double the 398,000 currently at risk, based on new maps released by the Federal Emergency Management Agency. The number of days with temperatures above 90 degrees is expected to jump sharply.

Environmental and business groups largely praised Mr. Bloomberg’s initiative, though some experts questioned whether the city needed to consider evacuating some areas.

“I think that the mayor’s plan is great,” said Robert S. Young, director of the Program for the Study of Developed Shorelines at Western Carolina University. “I really appreciate the fact that he acknowledges the problem and understands climate change and the fact that we need to prepare for it. But everyone needs to understand that you can’t guarantee protection for infrastructure that is in vulnerable locations, no matter how much money you throw at the problem.”