WASHINGTON — NASA scientists say the moon is currently in the nine-year half of its 18-year rotation around Earth where it is making high tides higher and low tides lower.
They say that, while high tides are currently not really higher than in the past, they will get significantly higher when the moon returns to this cycle of tide-boosting in the mid 2030s.
Here are the details: NASA reports that by the year 2035 every U.S. coastline will experience more high-tide floods — also called nuisance floods or sunny day floods — when the moon's rotational cycle will amplify rising sea levels caused by climate change.
In half of the moon's 18.6-year cycle, Earth's regular daily tides are suppressed, so high tides are lower than normal, and low tides are higher than normal.
In the other half of the cycle tides are amplified, so high tides get higher, and low tides get lower.
Global sea-level rise pushes high tides in only one direction — higher.
So half of the 18.6-year lunar cycle decreases the effect of sea-level rise on high tides, and the other half increases the effect.
NASA says the moon is currently actually in this tide-amplifying part of its cycle.
However, along most U.S. coastlines, this lunar boost has not really made high tides higher than in the past.
But NASA warns it will be a different story the next time the cycle comes around to amplify tides again, in the mid-2030s.
Because then, global sea-level rise would have been at work for another decade.
NASA says the higher seas, amplified by the lunar cycle, will cause a leap in the number of high-tide floods on almost all U.S. mainland coastlines, and also Hawaii and Guam.
Only far northern coastlines, including Alaska's, will be spared for another decade or longer because these land areas are being pushed upward by long-term geological processes.
