VIEW PHOTOS: New York recovers from Sandy

(CNN) -- Superstorm Sandy was no freak, say experts, but rather a hint of a coming era when millions of Americans will struggle to survive killer weather.

They're telling us we shouldn't be surprised that this 900-mile-wide monster marched up the East Coast this week paralyzing cities and claiming scores of lives.

"It's a foretaste of things to come," Princeton University professor Michael Oppenheimer told CNN. "Bigger storms and higher sea levels" will pile on to create a "growing threat" in the coming decades.

And New York, he warned, "is highly vulnerable."

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See submerged subway in Manhattan

Related: Superstorm Sandy breaks records

New York Mayor Michael Bloomberg has been strategizing.

His goal: mitigate future storm surges and flooding along the city's 500 miles of coastline.

That's a huge challenge. The densely populated city is dominated by some of the nation's most expensive real estate and is surrounded by a complex web of estuaries, tides and ocean.

Should New York think of its coastline as a threat? Is it the new Amsterdam? Maybe, say experts. But even a city as inventive as the Big Apple can only do so much.

The Intergovernmental Panel on Climate Change predicted in 2007 that the global average sea level would rise between 7 and 23 inches by the end of this century. More recent projections suggest that the melting of Arctic sea ice could mean a rise in excess of 30 inches. The New York State Sea Level Rise Task Force translated that into a local projection of 2 to 5 inches by the 2020s, and with rapid ice melt, the rise could be as much as 5 to 10 inches over the next 15 years.

New York dodged a bullet by inches last year as the remnants of Hurricane Irene bore down.

As Ben Orlove, director of the master's program in climate and society at Columbia University, wrote on CNN.com: "Irene also arrived at a time of especially high tides, and its storm surge came within inches of flooding the sea wall. Storms and tides are natural, but sea level rise is not. As it continues, New York grows more vulnerable."

Princeton's Oppenheimer, a professor of geosciences, recently modeled the effect of climate change on storm surges for the New York area.

In a paper published by Nature in February, he and three colleagues concluded that the "storm of the century" would become the storm of "every twenty years or less."

New York Gov. Andrew Cuomo agrees.

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"After what happened, what has been happening in the last few years, I don't think anyone can sit back anymore and say 'Well, I'm shocked at that weather pattern,' " Cuomo said Tuesday.

The conclusion of Oppenheimer and his colleagues is that storms will become larger and more powerful.

"Climate change will probably increase storm intensity and size simultaneously, resulting in a significant intensification of storm surges," they wrote. Sandy's diameter measured much larger than most storms.

A study of the New York area in 2010 led by Guy Nordenson, an architect and structural engineer whose offices are in Lower Manhattan, concluded: "There is a prevalent risk that the city will be severely paralyzed due to the predicted inundation and wave action associated with storm surge."

Related: Three lives changed forever by Sandy

If that's not bad enough, future superstorms may threaten drinking water, too.

Ocean saltwater could compromise the quality of drinking water and weaken ecosystems, Nordenson and others concluded in their book "On the Water: Palisade Bay."

But the answer, they argue, is not solely in engineering. "Cities fortify their coasts to protect real estate at the expense of nature ... (T)he hard engineering habit has proven costly, unreliable and ineffective."

Nordenson is helping Bloomberg study ways of turning New York's waterfront into more of a fortified castle to protect against invading superstorms.

The region needs a combination of strategies that includes more "soft infrastructure."

New York is losing tidal marshes at a rapid pace, partly because of the rise in sea level but also because of development.

Among the big ideas in "On the Water: Palisade Bay": Create an archipelago of islands and reefs in the New York-New Jersey Upper Bay to dampen powerful storm currents, the islands being "fingered" (with many inlets) and combining tidal marshes and parks.

Nordenson points to the example of the Netherlands and cities such as Hamburg, Germany, that incorporate flood plains into their planning. Similarly Hurricane Katrina showed the importance of preserving Gulf coastal swamps. He hopes a project with the Port Authority of New York and New Jersey to begin using dredged material for natural barriers will get under way soon.

Nordenson and his team of engineers, architects and designers showed some of their ideas at the Museum of Modern Art for an exhibition called "Rising Currents."

At the local level, the Nature Conservancy is working with communities in Long Island to identify the risks from rising sea levels and protect wetlands. Sarene Marshall, who leads the conservancy's Global Climate Change Team, estimates that every dollar spent in preventive measures saves $5 in disaster recovery, and that long-term investment in natural infrastructure is more effective than hard engineering. She points to the value of the humble oyster reef, nature's version of the sea wall.

Paul Greenberg, writing in The New York Times on Tuesday, echoes her point, saying that during past centuries oysters in the trillions "played a critical role in stabilizing the shoreline from Washington to Boston."

The Nature Conservancy estimates such reefs can reduce the storm risks for 7 million Americans living on the shore.

But islands, oysters and other measures to mitigate storm surges can't isolate New York from trends thousands of miles away in the Arctic. A growing body of evidence links the disappearance of summer ice cover in the Arctic with changing weather patterns.

Over three decades, about 1.3 million square miles of Arctic sea ice has disappeared, equivalent to 42% of the area of the lower 48 states.

Climate models previously projected that the Arctic might lose almost all of its summer ice cover by 2100, but some scientists said they believe the trend is accelerating and that it will be gone long before then.

"In addition to the extent of sea ice, what remains is thinner than it used to be," said Walter Meier of the National Snow and Ice Data Center at the University of Colorado at Boulder.

Here's how it works: Less sea ice means warmer water. Sea surface temperatures off the coast of the Northeast United States are now the highest ever recorded.

"It's like leaving the fridge door open," Meier said. The only way to restrain the process would be to moderate temperature increases, which in turn would depend on lowering carbon dioxide emissions.

Jennifer Francis at the Institute of Marine and Coastal Sciences at Rutgers University has shown that a warmer Arctic tends to slow the jet stream, causing it to meander and in turn prolong weather patterns. It's called Arctic amplification, and it may be helping entrench drought in the northwest United States and lead to warmer summers in the Northern Hemisphere.