Day 6

The Florida Keys flooded for 10 weeks straight and rising oceans could make this the new normal

The Florida Keys are cleaning up after being flooded for over 10 weeks because of king tides, naturally occurring high tides whose effects typically subside after several days. Scientists say climate change is making king tides higher and longer lasting.

Scientists say climate change is making king tides higher and longer lasting

King tide level waters combined with earlier storms and other factors has forced water onto the streets in parts of the Florida Keys. (Joe Raedle/Getty Images)
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Governments are busy trying to sort out the best ways to combat climate change, but in south Florida, residents are seeing its effects from the end of their docks.

Brian Boylan, a resident of Key Largo, Florida, told NPR he has noticed a six inch increase in water levels since he started living there.

But over the past few months, it got worse. Neighbourhoods in Key Largo were flooded by king tides that lasted for weeks, rather than weakening within several days as they typically do. These tides occur naturally, but scientists say they are being exacerbated by climate change and rising sea levels.

"If there's places now that already do have problems with king tide flooding, they're going to get it a whole lot more often," said Brian McNoldy, senior research associate at the University of Miami's Rosenstiel School of Marine and Atmospheric Science.

Here's part of his conversation with Day 6 host Brent Bambury:

King tides occur naturally — it has to do with the alignment of the earth and the sun and the moon. Can you explain what a normal king tide is?

In the big picture, kind of the informal term of king tide — it's not really an official term — but it refers to the highest tide of the year. It usually does occur on a new or full moon. 

So whenever there's a new or full moon, the sun, Earth and moon are all in a line and that does increase the high tides and the low tides. So from the August to November timeframe is when we're most likely to have those highest tides, and then that would fall on a full or new moon.

Low-lying areas like Key Largo, Fla., are likely to see more of these king tides as ocean levels rise, scientists say. (Joe Raedle/Getty Images)

How is climate change influencing what has been occurring naturally in the king tides? How is it changing them?

There's two big ingredients into how this happens. The first is the one that most people would think of, is that ice over either Antarctica or Greenland or any ice that exists on land, when that melts, that increases the average sea level around the world. 

But then a part two that's often missed, but it's actually about an equal amount of impact, is as the oceans warm they expand. So as climate change goes on and we get these warmer and warmer oceans, not only does that help melt more ice but it also is expanding the oceans themselves.

So for the people who live in these areas where king tides are already at their doorsteps, what kind of impact is this having on them?

I would have to imagine that most of them ... would see this as starting to get a bit old.

A lot of people who live in the Keys, they love to boat and fish but when the ocean comes to invade your house, it's probably a little bit less of an enjoyable spot to be.

So it's not easy. They have to usually choose when to go out to leave the house when the water might only be a few inches deep rather than a couple of feet. And it absolutely would have an effect on a car. You're driving through saltwater, which cars do not like. So it's an enormous inconvenience.

As king tide waters flood residential streets, it is estimated that the Florida Keys will likely see increased flooding as sea levels continue to rise. (Joe Raedle/Getty Images)

I understand that the king tides are more of an issue on the Atlantic coast than on the Pacific coast. Why is that?

I can probably think of about two reasons why it would be more exaggerated on the east coast.

The first is we do have the gulf stream that runs along the east coast and we do know that when that is not moving as quickly, that it causes sea levels to rise quite a bit. That same feature does not exist on the west coast. 

And then two, for the most part the areas along the coast on the east side are pretty flat, whereas the west coast cities, we generally don't think of as being really flat.

You're more prone to have a steeper incline off the coast … so you don't notice a few inches as much as you do on the east coast.

Areas of south Florida experienced flooding during king tides this fall. (Joe Raedle/Getty Images)

The Florida Keys are not densely populated. But what happens when places like Miami or Boston experience king tides, or if they start getting bad there? Will those cities have a plan in place to deal with this kind of inundation?

Speaking for the Miami area, there are things in place now and they're working on more to help places deal with this. It's not an easy problem, of course, because it's extremely expensive to either raise roads or install pumps. 

One of the things that they're talking about in the Keys now ... is more or less a managed retreat, where if there's places that flood so often, that it's probably worth just buying people out and just say let's give this land back to the ocean because it's not worth trying to keep this spot of land dry.


This Q&A has been edited for length and clarity. To hear the full interview with Brian McNoldy, download our podcast or click here to hear it on CBC Listen.

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