By damming rivers, humans have masked the full extent of surging sea levels, a new study finds. Sea levels have risen by an average of 16 centimetres since 1930, and they would have risen by an additional three centimetres but for the water tucked away in manmade reservoirs last century, not carefully tallied until now.
Consulting a worldwide dam registry, Ben Chao and students from the National Central University, Taiwan, estimated the volume of water stored in 29,484 reservoirs built since 1900. Measurements of sea-level rise have shown a variable rate of increase over the past 80 years. But by including the water stored year by year in dams, Chao's team revealed that sea level should, in fact, have risen steadily at a rate of 2.4 millimetres per year since 1930. Without the dams and reservoirs, seas would have risen as rapidly from 1960 to 1990 as before and after, a point not previously recognized.
The latest report from the Intergovernmental Panel on Climate Change did not include the water behind dams when quantifying the various factors contributing to rising seas. These results suggest seas might creep up faster than expected, boding ill for future coastlines, especially with dam-building now largely halted by environmental concerns.
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Barnett, A. Dammed sea rise. Nature Clim Change 1, 39 (2008). https://doi.org/10.1038/climate.2008.27
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DOI: https://doi.org/10.1038/climate.2008.27
