By the 2050s, more than 800,000 New York residents could be living in a flood zone that would cover a quarter of the city's land. Not only that, but New Yorkers could sweat out as many 32-Celsius days as is now normal for Alabama in the US' Deep South as effects of global warming take hold, a scientists' group convened by the city says.
With local waters higher than they are today, 8 per cent of the city's coastline could see flooding just from high tides, the group estimates. And while the average day could be significantly hotter, a once-in-a-century storm would probably spur a surge higher than Superstorm Sandy, which sent a record 4.3-metre storm tide gushing into lower Manhattan.
The updated predictions were released ahead of recommendations Mayor Michael Bloomberg is to present 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 would not hint at what the suggestions would be, what they might cost or how they might be financed. Many key decisions will likely 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," one of the study's overseers, Deputy Mayor Caswell 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.