Our overheating world is showing no mercy, and it will only get worse as time goes by. Climate change, the gravitational pull of the lunar cycle, and sea-level rise will increase dramatic flooding on most of the US coastline a new NASA/University of Hawaii study found. The flooding could last for weeks on end. Only Alaska will be spared, but only by a decade or two.
Carol Rasmussen of NASA’s jet propulsion Laboratory explains:
High-tide floods – also called nuisance floods or sunny day floods – are already a familiar problem in many cities on the U.S. Atlantic and Gulf coasts. The National Oceanic and Atmospheric Administration (NOAA) reported a total of more than 600 such floods in 2019. Starting in the mid-2030s, however, the alignment of rising sea levels with a lunar cycle will cause coastal cities all around the U.S. to begin a decade of dramatic increases in flood numbers, according to the first study that takes into account all known oceanic and astronomical causes for floods.
Led by the members of the NASA Sea Level Change Science Team from the University of Hawaii, the new study shows that high tides will exceed known flooding thresholds around the country more often. What’s more, the floods will sometimes occur in clusters lasting a month or longer, depending on the positions of the Moon, Earth, and the Sun. When the Moon and Earth line up in specific ways with each other and the Sun, the resulting gravitational pull and the ocean’s corresponding response may leave city dwellers coping with floods every day or two.
“Low-lying areas near sea level are increasingly at risk and suffering due to the increased flooding, and it will only get worse,” said NASA Administrator Bill Nelson. “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. NASA’s Sea Level Change Team is providing crucial information so that we can plan, protect, and prevent damage to the environment and people’s livelihoods affected by flooding.”
“It’s the accumulated effect over time that will have an impact,” said Phil Thompson, an assistant professor at the University of Hawaii and the lead author of the new study, published this month in Nature Climate Change. Thompson pointed out that because high-tide floods involve a small amount of water compared to hurricane storm surges, there’s a tendency to view them as a less significant problem overall. “But if it floods 10 or 15 times a month, a business can’t keep operating with its parking lot under water. People lose their jobs because they can’t get to work. Seeping cesspools become a public health issue.”
Why will cities on such widely separated coastlines begin to experience these higher rates of flooding at almost the same time? The main reason is a regular wobble in the Moon’s orbit that takes 18.6 years to complete. There’s nothing new or dangerous about the wobble; it was first reported in 1728. What’s new is how one of the wobble’s effects on the Moon’s gravitational pull – the main cause of Earth’s tides – will combine with rising sea levels resulting from the planet’s warming.
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. 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.
I did not see this one coming at all. Climate change is a threat multiplier, and we should brace ourselves for much disruption. Will our coastal communities adapt in time; I'm not holding my breath.
The study is behind a paywall.
Coastal locations around the United States, particularly along the Atlantic coast, are experiencing recurrent flooding at high tide. Continued sea-level rise (SLR) will exacerbate the issue where present, and many more locations will begin to experience recurrent high-tide flooding (HTF) in the coming decades. Here we use established SLR scenarios and flooding thresholds to demonstrate how the combined effects of SLR and nodal cycle modulations of tidal amplitude lead to acute inflections in projections of future HTF. The mid-2030s, in particular, may see the onset of rapid increases in the frequency of HTF in multiple US coastal regions. We also show how annual cycles and sea-level anomalies lead to extreme seasons or months during which many days of HTF cluster together. Clustering can lead to critical frequencies of HTF occurring during monthly or seasonal periods one to two decades prior to being expected on an annual basis.
