We should not be surprised. That's the view of many climate scientists as they survey the destruction wrought by the superstorm that ravaged the Northeast this week. The melting of Arctic ice, rising sea levels, the warming atmosphere and changes to weather patterns are a potent combination likely to produce storms and tidal surges of unprecedented intensity, according to many experts.
Recognizing the threat, New York City Mayor Michael Bloomberg is developing a strategy for mitigating the growing risk from storm surges and flooding along the city's 500 miles of coastline. In such a densely-populated area of so much expensive real estate, surrounded by a complex web of estuaries, tides and ocean, it is a huge challenge. And in the face of global changes, even a city as inventive as New York can only do so much.
The Intergovernmental Panel on Climate Change predicted in 2007 that the global average sea level would rise between seven and 23 inches by the end of this century. More recent projections suggest that the melting of 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 Arctic ice melt the rise could be as much as 5 to 10 inches over the next fifteen years. Combine that with a trend toward more intense storms and New York is "highly vulnerable," professor Michael Oppenheimer of Princeton University told CNN.
"(Superstorm) Sandy is a foretaste of things to come," he predicted, "from the combination of bigger storms and higher sea levels, both of which contribute equally to the growing threat."
New York dodged a bullet by inches last year as the remnants of Hurricane Irene bore down. 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."
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 Governor Andrew Cuomo appears to agree.
"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,'" he 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 had a diameter of some 900 miles, 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."
In addition, salt-water intrusion could compromise the quality of drinking water and weaken ecosystems,Nordenson and others concluded in the 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 ... the hard engineering habit has proven costly, unreliable and ineffective.
Nordenson is serving on a task force set up by Mayor Michael Bloomberg to study ways of giving New York a more resilient waterfront. He told CNN that 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 like Hamburg that incorporate flood plains into their planning. Similarly Hurricane Katrina showed the importance of preserving Gulf coastal swamps. He hopes a project with the New York Port Authority to begin using dredged material for natural barriers will get underway 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,
Paul Greenburg, writing in The New York Times Tuesday, echoes her point, saying that in previous centuries "a bivalve population that numbered 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 the past three decades, about 1.3 million square miles of Arctic sea ice has disappeared, equivalent to 42 percent 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 believe the trend is now 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.
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," said Meier. 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.
But there may be another effect
"Larger swings in the jet stream allow frigid air from the Arctic to plunge farther south, as well as warm, moist tropical air to penetrate northward," Francis wrote in Yale University's Environment 360 blog. That's pretty much what happened this week, a spectacular collision of Arctic and tropical weather fronts.
A recent article in the journal Oceanography shed more light on the consequences of Arctic ice melt. Charles Greene at Cornell University and others wrote that fundamental changes in the behavior of the jet stream will "stack the deck in favor of severe winter weather outbreaks in the United States and Europe into the foreseeable future."
Given the scale of the challenge, Oppenheimer and others believe there needs to be urgent remedial action to mitigate the effects, such as raising subway entrances and reinforcing the lower floors of buildings. At the moment, Oppenheimer said, there's a lot of evaluating hazards and too little action to address them.
After a sudden deluge in 2007 that closed part of the subway system, the New York Metropolitan Transit Authority committed more than $30 million to raise ventilation grates and redesign the entrances to some subway stations. It's also spent heavily on pumps, but a substantial surge would soon overcome such remedial measures. And beside the subway lines, power transformers and fiber-optic networks are vulnerable to flooding.
More ambitious actions would have far-reaching political and economic consequences. New York State's Sea Level Rise Task Force was created in 2007 and delivered its report to the legislature on the last day of 2010. Among its key recommendations was greater reliance on natural protection such as marshland and a tightening of zoning laws to prevent the loss of such features.
New York City disagreed with the panel's more critical recommendations, saying they did "not recognize the differences between undeveloped areas and densely populated cities." The city's own task force rejected the idea of limiting development as prohibitively expensive.
Douglas Hill of the Storm Surge Research Group at Stony Brook University has proposed a chain of massive sea barriers in Long Island Sound that could be closed to prevent flooding whenever a storm surge threatens. One would be close to the Verrazano Narrows bridge. (The Thames Barrier in London performs such a role in a more modest way.) But the cost would probably exceed $10 billion; a barrier in Venice cost $7 billion.
Among other options: tougher regulations on where industrial and chemical plants can be situated, improving the design of buildings to make lower levels flood-proof (known as freeboard in the insurance industry) and "soft edges" that better break wave action.
Stronger and maybe higher seawalls around more vulnerable
"It will be many generations, perhaps centuries, before the wall ... will have to be rebuilt or will even require any extensive repairs," the Times reported then. That was before climate change became part of the lexicon. New York City's "Vision 2020" plan warned that sea walls and other shoreline structures are likely to need more frequent repair because of more damaging storms.
Whether Sandy will drive the issue of climate change up the political agenda seems doubtful. According to a recent Pew Research Center poll, 67% of Americans believe the Earth is warming, up slightly since 2010, but that's 10 percentage points less than in 2006. Among both Democrats and Republicans, the percentage has declined, as has the number (now 64%) who say it's a serious problem
Sarene Marshall of the Nature Conservancy says the lack of debate about climate change in the presidential election campaign has been "unfortunate," but believes that Americans are getting to the point of recognizing what they see for what it is.