Coasts and properties along the U.S.’s heavily populated and developed Atlantic and Pacific coasts could be in for further sea level rise increases beyond the global average over the next century.

Kansas is looking more like home every year.

That might have been the notion occurring to some east and west coasters on the heels of back-to-back reports on projected sea level rise along much of the Atlantic and Pacific coastlines.

First the Findings for Pacific Coast

First came the National Academy of Sciences/National Research Council report projecting higher than global-average increases for much of the California coast. The extra oomph in part results from subsidence, with much of the projected coastal damages resulting from large waves, storm surges, and high tides, all fueled by a warming climate. The projected one-meter (about 39 inches) increase over the next century south of Cape Mendocino, in far-northern California, is “slightly higher” than projected global sea level increases.

The increase in sea level rise along the Washington, Oregon, and northern California coasts is expected to be about 60 centimeters. But it’s not time to break-out the champagne glasses: The researchers reported that an “earthquake magnitude eight or larger in this region could cause sea level to rise suddenly by an additional meter or more,” and such a quake is by no means out of the question, given the geology of the continental plate in the Cascadia Subduction Zone off the Washington and Oregon coasts. Such quakes have shaken the timbers “every several hundred to 1,000 years, most recently in 1700.”

The report by the Academy’s Ocean Studies Board committee projects global sea level increases of eight to 23 centimeters (3.1 to 9 inches) by 2030; 18 to 48 CMs (7 to 18.8 inches) by 2050, and 50 to 140 CMs (19.6 to 55 inches) by 2100, all relative to 2000 levels. Ice melt is “the dominant factor” in the increases, accounting for about 65 percent of the sea level rise, study chairman Robert A. Dalrymple, of Johns Hopkins University, said.

The larger ranges in the further-out years reflect inevitable uncertainties, he said in releasing the study. Those uncertainties relate to an incomplete understanding of the climate system; to a shortage of satellite data, going back only about 20 years; to inadequate global understanding of global ice masses; to modeling limitations; to unknowns concerning land underneath ice (“not sampled in a way that gives you exact conditions of ice melt”); and … of course … to future scenarios involving energy use.

Lots of damage along coast lines, and lots of erosion, the study projected, if high tides and other weather anomalies coincide in our future warmer climate … for instance, large waves getting larger, and short-duration sea level rises equivalent to what now might be an every-100-years event, Dalrymple said.

He agreed with a questioner during a press briefing that the committee’s projections generally are in sync with earlier estimates by IPCC and others. But he echoed a point made often expressed that IPCC had been “a little timid in 2007 about the ice contribution.”

Asked what policy recommendations the committee might have for affected areas, he said future steps rest with individual states to determine the urgency for planning and replied, “There are no recommendations in the report,” Dalrymple said.

And Now the Outlook (Worse) for the Atlantic Coastline

Misery loves company, and a separate report from U.S. Geological Survey researchers within days helped spread the pain.

A USGS study, published in Nature Climate Change, points to world-leading increases in sea level rise from Cape Hatteras, N.C., to just north of Boston, increases “three to four times faster than rates of sea level rise globally,” reporter Leigh Phillips wrote in Nature.

The Northeast coast “hotspot,” according to researchers from USGS’s Coastal and Marine Science Center in St, Petersburg, Fl., will experience increased sea level rise driven in part by effects of a warmer climate and in part by resulting freshening, and accompanying lower buoyancy, of surface waters as a result of increased ice melt.

The study points to sea level increases of between two and 3.7 millimeters (.08 and .14 inch) annually since 1980, compared with global increases of 0.6 to 1.0 millimeters (.02 and .03 inch) per year during that time. Looking ahead to 2100, they projected increases of between 20 and 29 centimeters (7.8 and 11.4 inches) beyond the projected global average increase of about 39 inches.

USGS said in a statement releasing the report that “the sea level rise hotspot is consistent with the slowing of Atlantic Ocean circulation. Models show this change in circulation may be tied to changes in water temperature, salinity and density in the subpolar north Atlantic.”

USGS Director Marcia McNutt, in that statement, said, “Many people mistakenly think that the rate of sea level rise is the same everywhere as glaciers and ice caps melt, increasing the volume of ocean water, but other effects can be as large or larger than the so-called ‘eustatic’ rise.” She said the study illustrates that regional oceanographic contributions must be considered in coastal planning efforts.

Differences in land movements, strength of ocean currents, water temperatures, and salinity can cause regional and local highs and lows in sea level, the agency said.

USGS quoted the study’s principal author, Asbury Sallenger, as saying, “Cities in the hotspot, like Norfolk, New York, and Boston already experience damaging floods during relatively low intensity storms.”

“Ongoing accelerated sea level rise in the hotspot will make coastal cities and surrounding areas increasingly vulnerable to flooding by adding to the height that storm surge and breaking waves reach on the coast.”

During the 21st century, increases in sea level rise rate that have already occurred in the “hotspot” will yield increases in sea level of 8 to 11.4 inches by 2100, USGS said. That increase would come on top of increases in global average sea level rise.

As the Nature article pointed out, the USGS study was published during a period of recent actions by some state legislatures — for instance, in North Carolina, Virginia, and Texas — to downplay climate change and global warming as factors affecting future sea level rise projections.

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