New York Mayor Michael Bloomberg on Tuesday announced a $20 billion plan to prepare for rising sea levels and hotter summers expected as a result of climate change in the coming decades.

The ambitious proposal, which could become the benchmark for other cities dealing with climate change, could reshape Lower Manhattan's waterfront, with the possible addition of a "Seaport City" out of the East Side.

The more than 400-page plan, which follows widespread destruction wreaked by Superstorm Sandy last year, included about 250 recommendations ranging from new floodwalls and storm barriers to upgrades of power and telecommunications infrastructures.

The plan also contained prosaic ideas, such as building up beaches and using sand dunes and plantings as natural buffers to storm surges flooding.

While some smaller provisions of the complex, long-term plan are already underway, others would require approval or action from the state or federal government.

A report commissioned by the city and issued alongside the proposals found that over the next 40 years, the number of sweltering summer days could double or even triple, making New York City as hot by mid-century as Birmingham, Alabama, is now.

By then, the sea level surrounding New York City could also rise by 2 feet (60 cm) or more.

Bloomberg's plan aims to ensure that the subway, transit, sewer and water, healthcare, energy and food distribution systems would continue to function for the city's 8 million people well into the future.

New York City could "do nothing and expose ourselves to an increasing frequency of Sandy-like storms that do more and more damage," Bloomberg said in remarks at the Brooklyn Navy Yard.

"Or we can make the investments necessary to build a stronger, more resilient New York, investments that will pay for themselves many times over in the years go to come" he said.

New York City is surrounded by 520 miles (835 km) of coastline, more than Miami, Boston, Los Angeles and San Francisco combined, and even a small rise in sea level would endanger lower-lying homes and businesses.

Sandy killed more than 100 people in New York, New Jersey and Connecticut, knocked out power to millions and cost New York City an estimated $19 billion in damages and lost economic activity. Bloomberg said a storm of Sandy's strength would cost nearly five times that amount if it hit the city in the middle of this century because of rising sea levels.

The implementation of the plan would be "an important step toward improved resilience for the City," said Mark Way, head of Sustainability Americas Swiss Re, whose catastrophe model was the basis for the city's analysis.

FLOODWALLS, DUNES AND TIDAL BARRIERS

In addition to new walls, dune systems and tidal barriers, the plan envisaged $1.2 billion in loans and grants to help owners make buildings more resilient to floods and proposed changes to the building code.

The plan also proposed the creation of new rules for how soon utility companies must restore power after a natural disaster. And the city would devise a plan to provide fuel when supplies are disrupted and to diversify energy sources.

Some elements of the plan are likely to be implemented this year, but others would stretch out in to decades, well beyond the 200 days that Bloomberg will remain in office.

"This is a call to the next administration and the next administration after that," said Chris Ward, former executive director of the Port Authority of New York & New Jersey.

To fund the plan the city would draw on money that has already been allocated for capital improvements and on post-Sandy federal relief funds approved by the US Congress.

But the funds may fall at least $4.5 billion short, and the city will have to delay, scale back or eliminate some proposals if it can't fill the gap, the plan's authors said.

Some thought the plan was more expensive than needed.

Jeroen Aerts, a professor of environmental risk management at the VU University in Amsterdam and an adviser to New York City who last month co-authored a study on New York's flood defense options, had expected the mayor to propose a plan estimated at $11.6 billion.

"I think Bloomberg chose a more expensive solution because he wants to add value to the city. He wants to involve developers and private companies," said Aerts. - Reuters