The moon is wobbling. This is nothing new. First observed in 1728, the wobble is a cyclical shifting of the moon’s orbit around the earth that takes 18.6 years to complete.

In half of this lunar cycle, Earth’s regular daily tides are diminished, with high tides lower than usual and low tides higher than usual. In the cycle’s other half, the situation is reversed, with high tides higher and low tides lower.

The bad news is that we are about to enter the second half of the cycle, which, coupled with rising sea levels is likely to result in increased coastal flooding. A new study by NASA scientists suggests that U.S. coastlines will face increased flooding during high tides in the mid-2030s thanks to the wobble magnifying rising sea levels caused by climate change.

“In the background, we have long-term sea level rise associated with global warming. It’s causing sea level to increase everywhere,” Ben Hamlington, NASA team leader and one of the study’s authors, told Reuters.

“This effect from the moon causes the tides to vary, so what we found is that this effect lines up with the underlying sea level rise, and that will cause flooding specifically in that time period from 2030 to 2040,” Hamlington said.

The study, published this month in the journal Nature Climate Change, was led by members of a NASA science team that tracks sea level change. The study focused on U.S. coasts but the findings are applicable to coasts worldwide, NASA said.

“This is eye-opening for a lot of people,” Hamlington said. “It’s really critical information for planners. And I think there’s a great amount of interest in trying to get this information from science and scientists into the hands of planners.”

How the moon’s “wobble” will impact coastal cities