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Can Ancient Sea Level Rise Prepare Us for the Future?

We talk with geologist and climate scientist Dr. Patrick Nunn, who has studied the history of sea level rise and its effect on human civilizations. This Pulsar podcast is brought to you by #MOSatHome. We ask questions submitted by listeners, so if you have a question you'd like us to ask an expert, send it to us at

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ERIC: From the Museum of Science in Boston, this is Pulsar, a podcast where we listen for answers to the most compelling questions we've ever gotten from our visitors. I'm your host, Eric. And sometimes our visitors ask us about the truth behind legends such as Atlantis, or other tales of lands disappearing beneath the seas. And it turns out, the truth can tell us a whole lot about our past, and can even help us prepare for our future. My guest today is Dr. Patrick Nunn, a geologist and climate scientist, and author of the new book Worlds in Shadow: Submerged Lands in Science, Memory and Myth. Dr. Nunn, thank you so much for calling in to Pulsar all the way from Australia.

PATRICK: Thank you very much, Eric. It's a real pleasure to be with you today.

ERIC: Now, you recently appeared on our series of adult programs, SubSpace, giving a talk about your work. And one of the first points you made is that sea level may be rising now, but it has not been static in the past, which is something that not a lot of us think about. Sea level going back a thousand, ten thousand, a hundred thousand years. So can you talk about how the oceans have changed over the whole course of human history?

PATRICK: Well, absolutely. So modern humans have been around on the earth for around two hundred thousand years. And in that period of time, the climate has changed. Now the reason the climate has changed is because the earth periodically moves further away in its orbit from the sun, and it becomes cooler, and then it moves back again and becomes warmer again. So whenever it moves further away, the earth cools down, and we go into an ice age. And during an ice age, what happens is that ice sheets form on the land. To form they need to get water from the ocean and freeze it and park it on the land. So whenever there's an ice age, the level of the ocean surface drops. And during the last great Ice Age, which peaked around twenty thousand years ago, the ocean surface was around four hundred feet lower than it is today. That's around 120 meters.

ERIC: Wow, that is a significant amount lower.

PATRICK: Yeah, so that was the situation during the last great ice age. So there was a lot more dry land on Earth. Of course not it was covered with ice. The key thing is that at the end of the last ice age, all that land started to melt, and the water from the melting ice poured into the oceans. And over the course of the next six hundred, seven hundred, eight hundred, or thousand years, depending on where you were in the world, the ocean surface rose by that same four hundred feet. And in doing so, of course, it flooded and submerge the fringes of the land. So all over the world, land masses were suddenly constricted in size. The United States, that area of land shrunk by about 31%. You know, and if that happened today, I mean, imagine what would happen to the land area of the United States. So this was not something trivial.

ERIC: Certainly, I can imagine that it impacted human civilization at the time in a huge way.

PATRICK: Now, of course, there weren't so many humans around at the time, but nevertheless, that impacted people. And a lot of my research has been trying to find ancient memories, embedded in myths and legends, as we like to call them, of the time when the sea level was rising and submerging these places. And that was etching itself in the minds of people. And some of those stories incredibly have come down to us today.

ERIC: So you had this amazing chart that you showed during your talk that had sea level over the last, say hundred thousand years, and its rise and fall. How do you construct that? Where do you start? Where do you get the evidence? Is it physical things you can go out and look for? Is it all based on modeling from we know how much ice there was, and therefore the water would have risen this much or fallen this much? How do you make that and make the maps? How do you start with something like that? That's a huge project.

PATRICK: The foundation is actually getting underwater and looking on the sea floor for ancient shorelines, and they're down there you know, typically around four hundred feet below the modern shoreline all around the world. We can find evidence of ancient shorelines, you know, whether those are submerged beaches or whether they're submerged cliff lines, or whether they're in a submerged sand dunes or whatever they are down there on the ocean floor. So that really I think gives us the first clue that the coastline was was different in the past. Of course modeling. We know how much ice formed on the land, and therefore we can calculate how much ocean water was needed in order to construct that much ice. But I wouldn't want the audience to think that this was something purely theoretical: it's not. It's absolutely grounded in observation. We know where the ocean surface was twenty thousand years ago, and the coldest time of the last ice age. And we know with a fairly high degree of certainty exactly how it rose in different places all around the world.

ERIC: And one of your other areas of expertise, as you mentioned, is looking at legends of the submerged cities, and how those legends persist over thousands or even tens of thousands of years. Your new book is Worlds in Shadow: Submerged Lands in Science, Memory and Myth. How do you go about investigating a myth and, kind of, seeing how you can trace it back to a real event?

PATRICK: I grew up in Europe with sort of surrounded or enthralled by myths and legends, because that's what we called them. And we always assumed that they were inventions of our distant ancestors, sort of culturally defined stories that had come down to us today. And, you know, they're exciting, but really nothing more than that. But what I realized through my training as a geologist and a climate scientist, is that a lot of these legends, not all of them, but a lot of these so-called legends have a basis in truth, particularly the stories of submerged lands. And all around northwest Europe, for example, there are stories of sunken cities below the ocean surface, and where people once lived. And because we don't know exactly where these were, and because we haven't actually found a lot of tangible evidence for these, because it's all washed away. We assume that they are fictions that they are made up stories. But of course, they are not. Because we can demonstrate that our ancestors were living in these places seven, eight, nine, ten thousand years ago, when the sea level was rising so rapidly. And when coastal lands were being submerged, and along with coastal lands, coastal towns, and coastal cities, and coastal fields, places where people want to live, places with which people had an affinity, were going underwater. And the experience of that must have been so incredibly traumatizing for these people, that they encoded their experiences and their memories of these things, into their oral traditions, into their stories, which they passed down from one generation to the next over sometimes thousands and thousands of years. And one of the reasons that I enjoy working in Australia, where I am at the moment, is that in Australia, you have probably the world's longest continuous culture. And people have been in Australia for around seventy thousand years. And most of that time they've been left alone, they haven't had other cultures coming in and mixing with them and sort of contaminating their oral legacy. So stories have been passed down amongst Indigenous Australian peoples for thousands and thousands of years. And a lot of the stories of submerged lands and submerged places, we can put minimum ages on with a high degree of precision. We can say all of these stories are at least seven thousand years old, because that's when the ocean surface around Australia reached its present level. And some of those stories must be even older than that seven, eight, nine, ten thousand years old, which is an incredible thing to think about. But it's only incredible because we doubt the ability of people who can't read and write to pass on information from one generation to the next. And I think that's something that a lot of scientists are now sort of looking at sideways and thinking, well, maybe we actually got that wrong. Maybe oral societies were actually far more efficient in storing and communicating information than we give them credit for.

ERIC: Maybe one of the most important points you made in your talk was that we're facing now sea level rise and climate change in a way that parallels our ancestors from thousands of years ago with cities becoming submerged. And that we can actually learn a lot from their adaptations, their reactions, how they processed it. So can you talk a little bit about maybe what is the most important thing we can learn from looking back at our history?

PATRICK: A lot of us today think, oh, my goodness, the climate is changing. This is completely unprecedented. You know, we have done something to upset this, this norm, this this unchanging climate norm that has existed in the past. But that's not true. Climate has forever been changing sea level has always been going up and down over over long periods of time. It's just that it's often not easy to detect that within the span of human life. I think today we can take some comfort from the fact that our distant ancestors did live with a rising sea level for generations upon generations. And they survived it. They got through it. And I don't think there's any question that humanity today, we'll get past this period of climate change. And this period of rising sea level, it will end eventually, probably about, you know, two hundred years from now. But in the interim, we need to learn to live with this. And then there are some specific lessons, I think that we can learn from our ancestors about how to live with this, maybe the first thing that we can learn is that short term adaptation like going out and building a seawall is really comforting in the short term. But from a lot of the research that I do in the Pacific Islands, I know that these seawalls tend to last, you know, sort of two, three, four years, and then they collapse and, and the process continues. So, there are real dangers that I think the experience of our ancestors teaches us about short term adaptation to a long term environmental stressor. And I don't mean that to sound too heavy. But you know, basically, if sea level is going to continue rising for even the next hundred years, building a seawall that's going to keep the sea out for the next ten years. You know, it seems like a really good idea at the time. But of course, it's not a really long term effective adaptation. And there's no question in my mind that we will see communities move from the coasts to higher areas inland, all over the world over the next hundred years or so. It's inevitable, and there's really not much we can do about that.

ERIC: Dr. Nunn, thank you so much for talking to us today.

PATRICK: It's been a real pleasure, Eric, thank you so much.

ERIC: You can check out more book launches and other awesome programs by checking out SubSpace, our adult offerings at the Museum of Science. Visit For the full schedule. Until next time, keep asking questions.

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