Despite how they appear from Earth, the celestial bodies’ complex, corkscrewing orbital paths through the cosmos are far from fixed, and subtle changes in how our planet, moon, and Sun all move and interact can have significant consequences for life here.

The moon’s orbit around Earth is one example of such a process. It does not simply circle the Earth in an endless perfect spiral, but its revolutions fluctuate, or “wobble,” as Nasa puts it.

This slow wobble either suppresses or amplifies Earth’s tides over an 18-year cycle.

High tides are higher during half of the cycle, and low tides are lower. Less extreme tides are recorded during the other half of the cycle. Meanwhile, the human-caused climate crisis means that sea levels can only rise.

This means that when the moon next wobbles its way into its amplification phase, which is expected to begin around 2030, higher tides and higher sea levels may combine to impact global coastlines, according to Nasa.

According to the agency, this will “cause a surge in flood numbers on almost all US mainland coastlines, Hawaii, and Guam.”

“Only the far northern coastlines, including Alaska’s, will be spared for another decade or longer as these land areas rise due to long-term geological processes.” High-tide floods, also known as nuisance floods or sunny day floods in the United States, are already a major concern in many cities along the Atlantic and Gulf coasts.

In 2019, the National Oceanic and Atmospheric Administration recorded more than 600 such floods.

However, once the moon’s next amplification phase begins, the country will face “a decade of dramatic increases in flood numbers,” according to Nasa’s assessment.

The new study, led by members of the Nasa Sea Level Change Science Team from the University of Hawaii, shows that high tides will exceed known flooding thresholds across the country more frequently. Furthermore, due to the relative positions of the moon, Earth, and sun, which can supercharge the gravitational effect on the sea, these floods are expected to occur in clusters lasting a month or longer.

When the moon and Earth revolve into specific alignments with each other and the sun, the resulting gravitational pull on the ocean “may leave city dwellers dealing with floods every day or two,” according to Nasa.

“Low-lying areas near sea level are increasingly at risk and suffering as a result of increased flooding, and the situation will only worsen,” Nasa administrator Bill Nelson said. “The moon’s gravitational pull, rising sea levels, and climate change will continue to exacerbate coastal flooding on our coasts and around the world.”

“NASA’s sea level change team is providing critical information so that we can plan, protect, and prevent damage to the environment and people’s livelihoods impacted by flooding,” he added.

According to Phil Thompson, an assistant professor at the University of Hawaii and the study’s lead author, “it’s the cumulative effect over time that will have an impact.” Because high-tide floods involve a small amount of water compared to hurricane storm surges, he believes they are viewed as a less serious problem overall.

“However, if it floods 10 or 15 times per month, a business cannot continue to operate with its parking lot submerged. People lose their jobs as a result of being unable to get to work. Seeping cesspools have become a public health concern,” he added.