By the 2050s, more than 800,000 New York City residents could be living in a flood zone that would cover a quarter of the city's land and New Yorkers could sweat out as many 90-degree days as is now normal for Birmingham, Ala., as effects of global warming take hold, a scientists' group convened by the city says.
With local waters a foot to 2½ feet higher than they are today, 8 percent of the city's coastline could see flooding just from high tides, the group estimates. And while the average day could be 4 degrees to nearly 7 degrees hotter, a once-in-a-century storm would likely spur a surge 5 or more feet higher than Superstorm Sandy, which sent a record 14-foot storm tide gushing into lower Manhattan.
The updated predictions were released Monday, ahead of recommendations Mayor Michael Bloomberg is to present Tuesday on what to do about threats that Sandy brought into stark relief.
"We have to look ahead and anticipate any and all future threats, not only from hurricanes and other coastal storms but also from droughts, heavy downpours and heat waves — many of which are likely to be longer and more intense in the years to come," an excerpt from the mayor's planned speech says.
Two top Bloomberg aides who oversaw the study, Seth Pinsky and Deputy Mayor Caswell Holloway, wouldn't hint at what the suggestions would be, what they might cost or how they might be financed. Many key decisions likely will come after Bloomberg's third and final term ends this year.
Bloomberg said last winter the study would examine the pros and cons of building berms, dunes, levees and other coast-protection structures. But he has historically been cool to the idea of massive sea walls — and emphatic about not suggesting that people move out of coastal areas.
City Hall, the state government and others have released warnings over the years about climate risks in the nation's most populous city. The city has required some new developments in flood zones to be elevated and has restored wetlands as natural barriers, among other steps.
"Sandy, obviously, increased the urgency of dealing with this and the need to plan and start to take concrete steps," Holloway said.
The new projections echo 2009 estimates from the scientists' group, called the New York City Panel on Climate Change, but move up the time frame for some upper-end possibilities from the 2080s to mid-century.
"The overall numbers are similar, but we have more compelling evidence now that (a more severe scenario from 2009) is looking like a more realistic possibility now," due to improved computer models and more evidence that some ice sheets are melting, said Radley Horton, a climate scientist with Columbia University's Earth Institute and a researcher with the city climate panel.
Scientists have reached a consensus on global warming, but still debate how severe the effects will be.
Meanwhile, the Federal Emergency Management Agency released revisions Monday to proposed new flood zone maps for the city. About 218,000 people and 35,000 buildings are in the current once-in-100-year flood zone, drawn in the 1980s. The new maps roughly double those numbers, though the revision shifts about 5,800 structures from a subset called the V zone — the area expected to suffer the worst damage — to a less stringent zone.
A roughly two-year review is expected before new maps become official. They can affect building regulations and insurance.
Associated Press writer Meghan Barr contributed to this report.