What the moon's 'wobble' could mean for coastal communities in Canada

A man looks out onto the Bay of Fundy in Hillsburn, N.S.. (THE CANADIAN PRESS/Andrew Vaughan)

TORONTO -

The moon’s orbit isn’t a perfect circle, and its elliptical path around the Earth could combine with rising sea levels to spell disaster for coastal communities.

A NASA study suggests that climate change’s impact on rising sea levels will only be amplified by the moon’s gravitational pull causing persistent high tides.

“When the moon is directly overhead, you actually feel a little bit lighter, just a miniscule amount, versus if the moon is on the other side of the Earth you actually feel a little bit heavier. The gravity of the moon is pulling you towards it, so we don't fully see it, we don't care, we don't feel an effect, but water, because there's so much of it, and it can move freely, does feel the effect,” Mubdi Rahman, an astronomer with the Toronto-based Sidrat Research, told CTVNews.ca in a phone interview on Thursday.

The moon doesn’t orbit on exactly the same angle as the Earth’s orbit, making it appear that it bobs around, hence the "wobble" known to scientists as the lunar nodal cycle.

“The moon orbiting around the Earth is not exactly aligned with the same axis that the Earth spins on. From our perspective, it's going to bounce up and down a little bit. Kind of like a spinning top that’s not exactly straight, it's going to wobble,” Jess McIver, assistant professor of physics and astronomy at the University of British Columbia, told CTVNews.ca in a phone interview on Thursday.

High tides occur when the moon’s gravity is pulling the water closer to it, and low tides occur when the Earth’s gravity is pulling the water down. While the areas of the Earth directly beneath the moon may be experiencing high tides, the sides of the Earth, which further away from the moon’s gravitational pull, won’t. But it’s not quite that simple.

“Much of it is dependent on the shape of the coastlines, where exactly you are, what the currents are,” Mubdi added.

The highest tides in the world belong to Canada’s Bay of Fundy, but Rahman says this has nothing to do with the moon’s position, it’s actually the shape of the bay and how the water gets in.

What the NASA study focuses on is the lunar nodal cycle when the moon is over specific parts of the Earth – specifically, the U.S..

“Some parts of the Earth are going to start to see the moon essentially rising overhead in a different way on about a 20-year timescale, and that's going to have a bigger effect on the tide,” said McIver.

According to NASA’s press release, the moon is currently in a tide-raising phase, but it doesn’t expect American coastal cities will see the seriously devastating effects of nearly daily flooding until its next cycle in the 2030s.

“Low-lying areas near sea level are increasingly at risk and suffering due to the increased flooding, and it will only get worse. 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,” ” NASA Administrator Bill Nelson said in a press release.

The flooding, according to the NASA press release, could happen several times a month.

“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,” Phil Thompson, an assistant professor at the University of Hawaii and the lead author of the new study, said in the release.

While Rahman anticipates this pattern will have a catastrophic effect on Canada, he said that it likely won’t be quite as impactful as what the researchers are anticipating in the U.S..

“One of the big things that is really helping Canada is that we don't build on the coast,” he said, referring to the Bay of Fundy being a national park with limited coastal structures.

He’s still concerned about Halifax, St. John’s, and other places that do feel the impacts of flooding, but he said that the moon isn’t picking any winners or losers here.

“It's just that those sea levels are rising, and that's through human-caused climate change,” he said.

The moon isn’t doing anything new or different. The new key factor is that climate change has resulted in rising sea levels.

“It's not just that the moon is going to make the tides stronger, which it will over time, but it's also the sea level rise,” said McIver.

The flooding may not look as dramatic as the scenes after hurricanes, but it will be more persistent flooding.

“We're not going to see pictures of cars and shops completely underwater all the time. It's going to be more relentless,” she said. “There will be times when we see day after day of water in the road, these constantly flooded routes that are maybe getting damaged over time. So, longer and more frequent stretches where structures that are really close to the water are inaccessible.”

While the moon wobble will have a period of more even tides, with high tides being lower and low tides being slightly higher, it won’t be enough to balance out the impact of the high tide phase.

“It’s that when it gets catastrophic and really high, it's really, really bad for us,” said Rahman.

It’s not just rising sea levels that are causing damage as the ocean’s tides ebb and flow. The deaths of billions of shellfish were a direct result of a low tide at an inopportune time.

“It's the really unfortunate intersection of the very bad heat wave we had here in Vancouver, and the tide killed off much of our shellfish,” said McIver.

Had it not been low tide, had the moon’s orbital position been in a different spot, those shellfish would have been covered by water and saved from being baked in the heat.

“It's really scary to see that intersection of tides and climate change,” she said.