"Hundreds of American cities are already locked into watery futures and we are growing that group very rapidly."
That's the message from Dr. Ben Strauss, the lead author of a new analysis of climate change data that shows the amount of carbon pollution already in the atmosphere could lead to "more than 4 feet of sea level rise past today’s levels" which would be enough, at high tide, to "submerge more than half of today’s population in 316 coastal cities and towns (home to 3.6 million) in the lower 48 states."
Strauss and his team released this interactive map to illustrate their findings:
According to the study the US cities most under threat from future coastal flooding are Miami, Virginia Beach, Va., Sacramento, Calif., and Jacksonville, Fla.
Those at a lessened but substantial risk include much larger cities like Boston, Long Beach, Calif., and New York City.
The analysis specifically looks at the level of "locked in" sea level rise. Writing at Climate Central, where he heads of the Program on Sea Level Rise, Strauss explains, "We have two sea levels: the sea level of today, and the far higher sea level that is already being locked in for some distant tomorrow."
By the end of this century, if global climate emissions continue to increase, that may lock in 23 feet of sea level rise, and threaten 1,429 municipalities that would be mostly submerged at high tide. Those cities have a total population of 18 million. But under a very low emissions scenario, our sea level rise commitment might be limited to about 7.5 feet, which would threaten 555 coastal municipalities: some 900 fewer communities than in the higher-emissions scenario.
To develop such figures, I combined my sea level debt findings with analysis from Climate Central’s Surging Seas project, which is a national assessment and mapping of coastal vulnerability in the U.S. based primarily on elevation and census data.
As Suzanne Goldenberg, the environment correspondent for the Guardian, explains:
[Strauss'] does not specify a date by which these cities, or parts of them, would actually fall under water. Instead, it specifies a "locked-in" date, by which time a future under water would be certain – a point of no return.
Because of the inertia built into the climate system, even if all carbon emissions stopped immediately, it would take some time for the related global temperature rises to ease off. That means the fate of some cities is already sealed, the study says.
Though the study specifically avoids predicting the rate of melting and planetary warming, it says that the ultimate threat to these coastal communities is "irreversible".
"In a loose analogy," writes Strauss, "it is much easier to know that a pile of ice in a warm room will melt, than to know exactly how fast it will melt."