While the study highlights the dire situation facing coastal cities, the lunar wobble is actually a natural occurrence, first reported in 1728. The moon’s orbit is responsible for periods of both higher and lower tides about every 18.6 years, and they aren’t dangerous in their own right. “In half of the Moon’s 18.6-year cycle, Earth’s regular daily tides are suppressed: High tides are lower than normal, and low tides are higher than normal,” NASA explains. “In the other half of the cycle, tides are amplified: 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 counteracts the effect of sea-level rise on high tides, and the other half increases the effect.” But this time around, scientists are more concerned. With sea-level rise due to climate change, the next high tide floods are expected to be more intense and more frequent than ever before, exacerbating already grim predictions. The study says these floods will exceed flooding thresholds around the country more often, and can also occur in clusters lasting more than a month. “During curtain alignments, floods could happen as frequently as every day or every other day,” the report adds. “Almost all U.S. mainland coastlines, Hawaii and Guam are expected to face these effects.”
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