State and total populations on land and major cities in which the majority of the U.S. population occupies land committed to fall below future high tide lines given emissions through 2100 under RCP 2.6 (blue city markers on both maps) or 8.5 (red city markers) and assuming the baseline Antarctic case. Only implicated cities with total populations exceeding 100,000 are shown; the marker radius is proportional to the total city population, ranging from 105,162 (Cambridge, MA) to 819,050 (Jacksonville, FL) persons. Graphic: Strauss, et al., 2015 / PNAS

By Kerry Sheridan
13 October 2015 Miami (AFP) – Say goodbye to Miami and New Orleans. No matter what we do to curb global warming, these and other beloved US cities will sink below rising seas, according to a study. But making extreme carbon cuts and moving to renewable energy could save millions of people living in iconic coastal areas of the United States, said the findings in the October 12 edition of the Proceedings of the National Academy of Sciences, a peer-reviewed US journal. Scientists have already established that if we do nothing to reduce our burning of fossil fuel up to the year 2100, the planet will face sea level rise of 14-32 feet (4.3–9.9 meters), said lead author Ben Strauss, vice president for sea level and climate impacts at Climate Central. The big uncertainty is the issue of when. “Some of this could happen as early as next century,” Strauss told AFP. “But it might also take many centuries,” he added. “Just think of a pile of ice in a warm room. You know it is going to melt, but it is harder to say how quickly.” To bring this issue home for people in the United States, the study pinpoints at-risk land where more than 20 million people reside. The authors projected business-as-usual carbon emissions, in addition to the complication of the melting West Antarctic ice sheet, a process some experts fear is irreversible. They also considered what might happen if the world were to make a big turnaround, reaching peak carbon emissions by 2020. This radical scenario would have to occur far earlier than the current aim of some world powers to peak by 2050, said Strauss. An online tool at Climate Central allows users to see the impacts on various US cities. A global version is expected in the next month, Strauss said. The tool shows which US cities may face “lock-in dates beyond which the cumulative effects of carbon emissions likely commit them to long-term sea-level rise that could submerge land under more than half of the city’s population,” said the study. “Norfolk, Virginia, for example, faces a lock-in date of 2045 under a scenario of unabated carbon emissions.” For cities like Miami and New Orleans, the limits are already exceeded. “In our analysis, a lot of cities have futures that depend on our carbon choices but some appear to be already lost,” Strauss said. “And it is hard to imagine how we could defend Miami in the long run.” Miami’s low elevation and porous limestone foundation mean that sea walls and levees will not help, he said. […] “New Orleans is a really sad story,” Strauss said. “It is a lot worse looking than Miami.” [more]

Sea level rise will ‘swallow Miami, New Orleans’

ABSTRACT: Anthropogenic carbon emissions lock in long-term sea-level rise that greatly exceeds projections for this century, posing profound challenges for coastal development and cultural legacies. Analysis based on previously published relationships linking emissions to warming and warming to rise indicates that unabated carbon emissions up to the year 2100 would commit an eventual global sea-level rise of 4.3–9.9 m. Based on detailed topographic and population data, local high tide lines, and regional long-term sea-level commitment for different carbon emissions and ice sheet stability scenarios, we compute the current population living on endangered land at municipal, state, and national levels within the United States. For unabated climate change, we find that land that is home to more than 20 million people is implicated and is widely distributed among different states and coasts. The total area includes 1,185–1,825 municipalities where land that is home to more than half of the current population would be affected, among them at least 21 cities exceeding 100,000 residents. Under aggressive carbon cuts, more than half of these municipalities would avoid this commitment if the West Antarctic Ice Sheet remains stable. Similarly, more than half of the US population-weighted area under threat could be spared. We provide lists of implicated cities and state populations for different emissions scenarios and with and without a certain collapse of the West Antarctic Ice Sheet. Although past anthropogenic emissions already have caused sea-level commitment that will force coastal cities to adapt, future emissions will determine which areas we can continue to occupy or may have to abandon.

Carbon choices determine US cities committed to futures below sea level