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.
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."
Urgent remedial action
There needs to be urgent remedial action to mitigate the effects, said Oppenheimer, such as raising subway entrances and reinforcing the lower floors of buildings. At the moment, Oppenheimer said, there's a lot of evaluation of 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 it did "not recognize the differences between undeveloped areas and densely populated cities." The city's task force rejected the idea of limiting development as prohibitively expensive.
Other ideas aimed at protecting New York include:
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.