Twenty-two kilometers of salt water separates the island of Jersey from France. But it didn’t used to. Photo by Mauritius images GmbH/Alamy Stock Photo
It wasn’t long after Henry David Inglis arrived on the island of Jersey, just northwest of France, that he heard the old story. Locals eagerly told the 19th-century Scottish travel writer how, in a bygone age, their island was much more substantial, and that folks used to walk to the French coast. The only hurdle to their journey was a river—one easily crossed using a short bridge.
“Pah!” Inglis presumably scoffed as he looked out across 22 kilometers of shimmering blue sea—because he went on to write in his 1832 book about the region that this was “an assertion too ridiculous to merit examination.” Another writer, Jean Poingdestre, around 150 years earlier, had been similarly unmoved by the tale. No one could have trod from Jersey to Normandy, he withered, “vnlesse it were before the Flood,” referring to the Old Testament cataclysm.
Yet, there had been a flood. A big one. Between roughly 15,000 and 5,000 years ago, massive flooding caused by melting glaciers raised sea levels around Europe. That flooding is what eventually turned Jersey into an island. Rather than being a ridiculous claim not worthy of examination, perhaps the old story was true—a whisper from ancestors who really did walk through now-vanished lands. A whisper that has echoed across millennia.
That’s exactly what geologist Patrick Nunn and historian Margaret Cook at the University of the Sunshine Coast in Australia have proposed in a recent paper. In their work, the pair describe colorful legends from northern Europe and Australia that depict rising waters, peninsulas becoming islands, and receding coastlines during that period of deglaciation thousands of years ago. Some of these stories, the researchers say, capture historical sea level rise that actually happened—often several thousand years ago.
For scholars of oral history, that makes them geomyths. “The first time I read an Aboriginal story from Australia that seemed to recall the rise of sea levels after the last ice age, I thought, No, I don’t think this is correct,” says Nunn. “But then I read another story that recalled the same thing.”
Nunn has since gathered 32 groups of stories from Indigenous communities around the coast of Australia—a continent nearly as large as Europe—that seem to refer to geological changes along shorelines. Take the legend of Garnguur, told by the Lardil people, also known as Kunhanaamendaa, in the Wellesley Islands, off northern Australia. It describes a seagull woman, Garnguur, who cut the islands off from the mainland by dragging a giant raft, or walpa, back and forth across a peninsula.
In some versions of the story, this is punishment for her brother, Crane, who failed to look after her child when asked. Nunn and Cook argue that the narrative can be taken as a memory of how, no more than 10,000 years ago, melting glaciers caused the Wellesley Islands to be cut off from the mainland. Interestingly, there is a large underwater trench between two of the Wellesley Islands—perhaps a feature of the seabed that prompted the image of Garnguur plowing her raft into the earth, the researchers suggest in their paper.
Separately, other Indigenous groups in South Australia, such as the Ngarrindjeri and Ramindjeri, tell of a period when Kangaroo Island was once connected to the mainland. Some say it got cut off by a big storm, while others describe a line of partially submerged boulders that once allowed people to cross to the island.
For Jo Brendryen, a paleoclimatologist at the University of Bergen in Norway who has studied the effects of deglaciation in Europe following the end of the last ice age, the idea that traditional oral histories preserve real accounts of sea level rise is perfectly plausible.
During the last ice age, he says, the sudden melting of ice sheets induced catastrophic events known as meltwater pulses, which caused sudden and extreme sea level rise. Along some coastlines in Europe, the ocean may have risen as much as 10 meters in just 200 years. At such a pace, it would have been noticeable to people across just a few human generations.
“These stories are anecdotes, but enough anecdotes makes for data,” Brendryen explains. “By systematically collecting these kinds of memories or stories, I think you can learn something.” Beyond capturing historical events, geomyths offer a glimpse into the inner lives of those who were there, says Tim Burbery, an expert on geomyths at Marshall University in West Virginia, who was not involved in the research: “These are stories based in trauma, based in catastrophe.”
That, he suggests, is why it may have made sense for successive generations to pass on tales of geological upheaval. Ancient societies may have sought to broadcast their warning: beware, these things can happen! “They would mythologize it,” Burbery adds. “They would use the language of legend, and within that there could be some real data.”
Today, many people report a sense of eco-anxiety because of climate change and its effects, including sea level rise. Nunn points out that our contemporary situation differs in some ways from ancient predicaments—there are many more humans on the planet and huge, densely populated coastal cities, for example. And unlike historical periods of deglaciation, we are today both the agents and victims of rapid environmental change.
But vulnerability to climatic shifts allows us to feel an affinity toward our forebears. And the old stories still have things to teach us. As Nunn says, “the fact that our ancestors have survived those periods gives us hope that we can survive this.”
Critics by Zeke Hausfather
The Earth’s climate has been quite stable over the past 11,000 years, playing an important role in the development of human civilisation. Prior to that, the Earth experienced an ice age lasting for tens of thousands of years. The past million years of the Earth’s history has been characterised by a series of ice ages broken up by relatively short periods of warmer temperatures.
These ice ages are triggered and ended by slow changes in the Earth’s orbit. But changing atmospheric concentrations of CO2 also plays a key role in driving both cooling during the onset of ice ages and warming at their end. The global average temperature was around 4C cooler during the last ice age than it is today. There is a real risk that, if emissions continue to rise, the world warms more this century than it did between the middle of the last ice age 20,000 years ago and today.
In this explainer, Carbon Brief explores how the last ice age provides strong evidence of the role CO2 plays as a “control knob” for the Earth’s climate. It also acts as a cautionary tale of how the climate can experience large changes from relatively small outside “forcings”.
The Earth has experienced a number of periods over the past million years in which large continental ice sheets have covered much of the northern hemisphere. These ice ages are associated with a large drop in global temperatures – 4C or more below today’s levels – with much larger changes over land and in the high latitudes.
These ice ages are punctuated by “interglacial” periods where temperatures rise to around current levels. The most recent ice age occurred between 120,000 and 11,500 years ago, while the current interglacial period – the Holocene – is expected to last for additional tens of thousands of years (and human activity may inadvertently delay the start of the next ice age even further).
Ice-age cycles are primarily driven by periodic changes in the Earth’s orbit. Three distinct orbital cycles – called Milankovitch cycles after their discoverer, Serbian scientist Dr Milutin Milankovitch – interact to change the distribution of incoming solar energy in ways that can dramatically affect the Earth’s climate.
- Precession – a 26,000-year shift in the orientation of Earth’s axis of rotation that affects how much summer sun is received at high latitudes (and shifting how much reaches the north vs south).
- Obliquity – a 41,000-year change in the tilt of the Earth’s axis relative to the sun that changes how much sun is received during a year at the poles versus the equator.
- Eccentricity – a 100,000-400,000 change in the shape of the Earth’s orbit around the sun that alters the length of the seasons and affects the importance of precession.
These three cycles overlap in different ways over time given their different periods, which means that ice ages do not always have the same duration. None of these cycles substantially changes the total amount of energy reaching the Earth from the sun; rather, they mostly act to change the distribution of the sun’s energy across the surface of the Earth.
When these cycles cause the northern latitudes to get less sun in the summer, it allows ice sheets to begin to expand. These ice sheets in turn reflect more incoming sunlight back to space, resulting in a “positive feedback” that drives additional regional cooling.
The northern latitudes matter much more than the southern latitudes – at least over the past few million years – as it contains more land area (which can more easily become ice-covered than the oceans) and because the Antarctic has remained covered in ice…..To be continued