Day of the Fronds, 6th of Spring, 526 M.E. (Aldebaran): Oh, fun! There's another new climate-change study out! This one, as reported by the NY Times, found that previous studies of sea-level rise have underestimated just how high the water actually already is. It turns out hundreds of millions of people worldwide are already living dangerously close to the rising ocean than previously estimated.

The study, published in the journal Nature, found that coastal sea levels are, on average, eight inches to a foot higher than many maps and models of the world’s coastlines indicate.  The discrepancies are most pronounced in Southeast Asia and Pacific nations, where coastal sea levels are up to several meters higher than commonly estimated.

The study concludes that scientists have often been working from the wrong starting point when calculating what land and populations might be affected in the future. In other words, they were underestimating where coastal sea levels already are. Of course, people who are exposed to tidal floods know exactly where the ocean is.  

The problem centers on a decades-old method that compares satellite-based measurements of land elevation to what scientists call the “geoid model,” which estimates average sea level based on the Earth’s gravitational field. This method, once considered state-of-the-art and commonly taught in graduate schools, doesn't take into account factors like currents, winds, and tides, which can also influence sea levels but are not included in the geoid model. Sea levels are most accurately estimated when all factors are considered and combined correctly.

Some 90 percent of the papers reviewed in the study relied only on the method of mapping sea levels using Earth’s gravitational field. Another 9 percent of the papers, most of which are relatively recent, did use both kinds of data, but failed to combine them correctly.

In general, the findings indicate that hundreds of millions more people — particularly in Vietnam, the Philippines, Indonesia, the Maldives, and other Southeast Asian and Pacific nations — are living closer to sea level than widely assumed by Western experts and policymakers. In other words, methods of studying sea-level rise that seemed to work relatively well for coastlines in Europe or the U.S. lead to bigger discrepancies in other parts of the world.