Keeping score on Earth’s rising seas

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An international collaboration among dozens of scientists has come within less than a millimeter of attaining a long-sought goal: accounting for all the jostling, overlapping, and constantly changing contributions to global sea-level rise.

A just-published paper assembles virtually all the puzzle pieces – melting ice, warming and expanding waters, sinking coastlines and a stew of other factors – to arrive at a picture of remarkable precision. Since 1993, global sea level has been rising by an average 3.1 millimeters per year, with the rise accelerating by 0.1 millimeter per year, according to the study published Aug. 28 in the journal, “Earth System Science Data.”

“Global mean sea level is not rising linearly, as has been thought before,” said lead author Anny Cazenave of France’s Laboratory for Studies in Geophysics and Oceanography (LEGOS). “We now know it is clearly accelerating.”

The paper’s main achievement, however, is its declaration of near “closure” for the global sea level budget. Much like balancing a household checkbook, scientists have been working for decades to correctly account for all the factors contributing to the observed rate of sea-level rise.

An ice-choked fjord in Greenland. Image credit: NASA/JPL-Caltech.

And it’s a far trickier proposition