Should a newly published sea level rise scenario come to pass, hundreds of American landmarks, neighborhoods, towns and cities would be submerged this century, at least in the absence of engineering massive, costly and unprecedented defenses and relocating major infrastructure. Ocean waters would cover land currently home to more than 12 million Americans and $2 trillion in property.

This extreme rise scenario, considered unlikely but increasingly plausible, was published together with other projections in a technical report by the National and Oceanic Atmospheric Administration in January. NOAA added “extreme” as a new sea level category in the publication, supplementing high, intermediate and low categories that have also been used in past reports. The new term reflects recent research suggesting that some parts of the Antarctic ice sheet may begin to collapse much sooner than scientists had previously anticipated, particularly if ongoing emissions of heat-trapping gases like carbon dioxide and methane remain high.

The extreme scenario would mean roughly 10 to 12 feet of sea level rise by 2100, depending on location, for all coastal states but Alaska — a significant departure above the global average projection (just over 8 feet).  Detailed local projections are available from NOAA.

The impacts of this […]