NEW YORK -- Mayor Michael Bloomberg has given his city one of the most detailed and highly publicized plans to reduce carbon emissions and to adapt to rising sea levels and other risks posed by climate change.

He launched his program in 2007 and used it as a platform to vault into the chairmanship of C40, an international group of 40 big-city mayors determined to deal with the complex welter of climate issues they face. "Mayor Bloomberg is shaping the global dialogue and action on climate change in cities," boasts the latest version of New York City's plan, known as "PlaNYC."

SPECIAL SERIES Cities hold half the world's population and produce more than 70 percent of the world's greenhouse gas emissions. While they have heightened risks from floods, storms and sea-level rise, they are often left out of national and global warming talks. This series shows how some are beginning their own plans to deal with a more hostile climate.

While Mitt Romney and other major Republicans sow doubts about climate issues and many Democrats -- including at times President Obama -- have soft-pedaled them, Bloomberg's plans appear to confront the difficulties of climate change head-on. "The scientific evidence is irrefutable," PlaNYC says. "Rising sea levels are extremely likely," says the New York City Panel on Climate Change, appointed to advise the city on carrying out the plan.

Bloomberg has one built-in advantage. He oversees a city that has only one-third of the greenhouse gas emissions of the average U.S. city because New York has the largest underground subway and commuter train network in the United States. More than half of its densely packed population doesn't own a car.


But there is also a steep downside. Because New York City has more than 520 miles of coastline, it is among the top 10 port cities in the world that are most exposed to coastal flooding. Measured in terms of private property subject to damage from more potent storms and torrential rains that scientists predict are coming with climate change, the low-lying Big Apple ranks second in the world, with $2.3 trillion of property at risk, according to its own data.

One of the first victims of the flooding will likely be the same underground transit systems that make New York's carbon dioxide emissions so low. A recent report by the New York State Energy Research and Development Authority warned that the combination of sea-level rise and the surging ocean currents that can accompany a powerful storm could flood many of the city's subway, highway and rail tunnels "in less than one hour."

According to state and federal estimates, the resulting damage could take weeks, even months, to repair. The New York state study estimates that the economic losses from a once-in-100-years storm, including workers unable to get to work, could range from $58 billion to $84 billion, depending on the extent of sea-level rise and the size of the storm.

Close calls in the past

"I think you could drown a lot of people very easily. All it takes is water going into the subway," said Malcolm Bowman, a professor of physical oceanography at the State University of New York at Stony Brook. He is the leader of a group of scientists at the university who have been looking at models of storm surges and ways, including building some large ocean barriers, that might help New York protect itself.

Bowman said New York has already had some close calls. A powerful winter storm in 1992 shut down the subway's power, and rescue crews had to evacuate passengers from flooding tunnels. Because of the peculiar shape of New York's harbor, big storms have a tendency to pile up water at the Battery on the southern tip of Manhattan -- an area rich with street-level subway and train tunnel entrances.

Subway deluge

Last fall, when Hurricane Irene gave the city a glancing blow, Bowman stationed himself there at a flood gauge. "I was watching the sea level, and it came within an inch and a half of what it was in '92."

The damage of a major flood could extend far beyond subway passengers because much of the city's electrical power lines and communications systems is buried in or near the same tunnels. Bowman and other engineers who have studied the problem think it's time for the city to consider building storm surge barriers, adjustable floodgates in the harbor that can let shipping through but are able to close to slow or block a storm surge.

The Netherlands and England have built their barriers. Italians are building one to protect Venice, and the Russians are completing a system that would protect St. Petersburg. Estimates for building a barrier or network of barriers to protect New York City and its surroundings begin at about $10 billion.

Bowman, a past member of Bloomberg's committee focused on climate change, said that, so far, city officials have resisted the idea. "It was clear they didn't really want to go there," he said. "I don't know why; too expensive, too ambitious, I guess."

According to Adam Freed, deputy director of New York's Long-Term Planning and Sustainability Office, Bloomberg has committed to completing 132 initiatives in his climate plan before he leaves office next year. So far, building storm surge barriers is not among them.

Strategies still under study

However, Freed noted that David Bragdon, who heads the long-term planning office, told the City Council in December, "We are evaluating a wide variety of coastal protection strategies, from wave attenuators and soft edges to storm surge barriers." Bragdon added, "We are not presupposing the outcomes of this or other studies under way."

Last week, Caswell Holloway, New York's deputy mayor for operations, said the city was preparing to invest more than $1 billion in projects that promote "climate resilience." Some of the strategies that Bragdon and Holloway have discussed come from teams of architects who presented an exhibit in 2010 at the city's Museum of Modern Art on how they would redesign New York's harbor to cope with rising sea levels.

They recommended using "soft infrastructure," including constructing a network of tidal wetlands, salt marshes and an irregular, parklike coastline with "fingers" of land extending into the sea that would "attenuate" or take some of the power out of storm-driven waves.

"The mayor's office has done wonderful things in terms of funding studies, but we haven't come to real engineering solutions," said Klaus Jacob, a geophysicist and environmental disaster expert at Columbia University. He wrote the portion of the New York state climate change plan that described in detail how flooding could knock out the city's rapid transit systems.

The state plan envisions a 100-year storm hitting the city. It estimates that 1 billion gallons of seawater might have to be pumped from subway and train tunnels. Because salt water is corrosive, repairing or replacing subway equipment once the water leaves could take months before the system is restored.

The state plan suggests some short-term fixes, such as elevating street-level subway entrances and rebuilding collapsed flood walls at subway rail yards. It proposes medium-term measures that would begin over the next 30 years. They would include building "estuary-wide storm barriers" with floodgates that could close and protect the city from the engineers' nightmare scenario, which is a storm surge riding into the city on top of a high tide.

Then there are long-term strategies including "retreat options," or plans to evacuate parts of the city being reclaimed by a rising sea.

Storm surge barriers and the 'Katrina effect'

The study says because of the potential of billions of dollars in damage, the city might find it cost-effective to begin spending now for protective measures, including the surge barriers, starting with "hundreds of millions of dollars" per year.

Jacob proposes a carbon tax to help finance a barrier system, but he regards it as an "interim solution," because although the surge barriers might be built within 30 years, scientists expect sea levels to continue rising long after that, driven by melting glaciers and the expansion of warming water.

Storm surge barrier

He worries about what he calls the "Katrina effect," describing how New Orleans politicians gained the illusion of protection from high sea walls, only to see them overtopped by Hurricane Katrina in 2005. "Ultimately, the same thing that happened in New Orleans will happen here, only it will happen later."

The dilemma the Bloomberg administration is facing is not just of its own making. The federal government is responsible for mapping floodplains, or areas at risk of flooding, and its maps haven't been updated since 1983. Currently, according to city officials, 200,000 New Yorkers live in them, including Robert Trentlyon, who lives in lower Manhattan's fashionable Chelsea neighborhood.

A long-term civic activist, he began by pondering one of the city's "vision statements" that set out "resilience" as part of its strategy to protect against sea-level rise. "If we get flooded, the water will leave, then we'll fix it up again and wait another 50 years and then it will happen again," is the way he describes it.

'Flooding is a bad thing here'

That put Trentlyon, 82, on the warpath. He began appearing before neighborhood groups. He remembered telling a group of businessmen how, once the flooding occurred, it might take weeks or months to restore the subway. "That was what they seized on. Most of them and their employees take the subway to work."

Trentlyon and allies began buttonholing City Council members and state senators, building up pressure that may have led to the city's current study of the problem. While experts say storm surge barriers could be built in 10 years, the matter of reaching a political decision to build them in Europe has sometimes taken two or more decades. "I would like to get all the candidates who are running for mayor to take a position on this," Trentlyon said.

It would help future New York City officials if all of the pieces of the flooding problem were under their control, but they aren't. The city's subway system, for example, is run by the Metropolitan Transportation Authority (MTA), which is a state agency.

"Flooding is a bad thing here," acknowledged Thomas Abdallah, the subway's chief environmental engineer. Because groundwater seeps into the 107-year-old system, the MTA must pump out 8 million gallons a day, even when it doesn't rain.

"When the city sewers clog, where else does the water go? It goes to us," he added. "When it rains, we have rains coming through gratings and through subway entrances." He has vivid memories of 5-inch rain in August 2007. It started at 5 a.m., ending rush hour before it could start. "Just about all of New York City had to walk to work that day."

Abdallah still has trouble convincing New Yorkers that climate change has the power to stop the heartbeat of this legendarily bustling city. "Last year, when we had the severe snow, people would call me and say, 'Hey, where's your global warming now?' I said, well, the science is really very consistent. I think sometime in the next five years, the 100-year storm will be re-evaluated to something like a 30-year storm."

Reporter Colin Sullivan contributed.

Tomorrow: Updating a million buildings.