Moon ‘Wobble’ Spells Trouble for Coastal Towns

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First recorded in 1728, the moon’s wobble is nothing new. KQED describes the phenomenon as a “regular oscillation in the lunar orbit,” an ongoing cycle that takes about 18.6 years to complete. 

But the wobble isn’t just a curiosity—it also has a major effect on high tides and flooding. That effect is even stronger than previous evidence suggested, according to a new report.

A new study led by NASA Sea Level Change Science Team from the University of Hawaii shows that when the moon, earth and sun align specifically, the ocean’s corresponding response leads to floods and high tides due to the gravitational pull. Add that natural cycle to sea level rise caused by global warming and a troubling data set emerges.

“Low-lying areas near sea level are increasingly at risk and suffering due to the increased flooding, and it will only get worse,” NASA Administrator Bill Nelson said in the report. “The combination of the moon’s gravitational pull, rising sea levels and climate change will continue to exacerbate coastal flooding on our coastlines and across the world.”

In the 15th century, Sir Isaac Newton discovered that tides were connected to the moon’s orbit, generally causing two high tides every 24-hour period. But because the moon’s orbit is slightly tilted, “the path of the moon’s orbit seems to fluctuate over time, completing a full cycle—sometimes referred to as a nodal cycle—every 18.6 years,” according to a description in the New York Times. “At certain points along the cycle, the moon’s gravitational pull comes from such an angle that it yanks one of the day’s two high tides a little bit higher, at the expense of the other. This does not mean that the moon itself is wobbling, nor that its gravity is necessarily pulling at our oceans any more or less than usual.”

Right now, the moon’s wobble cycle is amplifying high tides, but the effects of sea level rise have not yet set in. Over the next several years, the wobble will suppress high tides, but in the 2030s, the earth will see a combination of sea level rise and the effects of the moon’s amplifying wobble. 

“The moon is in the tide-amplifying part of its cycle now. However, along most U.S. coastlines, sea levels have not risen so much that even with this lunar assist, high tides regularly top flooding thresholds,” a NASA press release detailed. “It will be a different story the next time the cycle comes around to amplify tides again, in the mid-2030s. Global sea level rise will have been at work for another decade. The higher seas, amplified by the lunar cycle, will cause a leap in flood numbers on almost all U.S. mainland coastlines, Hawaii and Guam.”

The National Oceanic and Atmospheric Administration (NOAA) documents changes in high-tide flooding patterns and said sea level rise continues during a full-moon tide or with a change in prevailing winds or currents. NOAA reported that high tides already exceed known flooding thresholds around the United States.

NASA’s Sea Level Change Team is providing information to the public so planning and preventing damage to the environment can come into effect. Ben Hamlington, leader of NASA’s Sea Level Change Team, said findings of the new study are a vital resource for coastal urban planners who are focused on preparing for extreme events rather than high-tide floods.

“From a planning perspective, it’s important to know when we’ll see an increase,” Hamlington said. “Understanding that all your events are clustered in a particular month, or you might have more severe flooding in the second half of a year than the first, that’s useful information.”

Though high tides and flooding effects will vary, experts think the California coast will be affected by the next wobble cycle.

“The assessment we made for the tide gauge in San Francisco is that we’d see about a five time increase in the number of high-tide flood days,” Hamlington said, according to KQED.