Un changement climatique a failli noyer Jaime ? - Sous Nos Pieds #9

After 6 seasons of strategy, politics and betrayal, the writers of Game of Thrones had decided for the 7th season to offer fans what they were looking for. A confrontation between a horde of Dothrakis, the Lannister army, and 3 dragons. An epic battle, staged with stunning special effects, which ended with the possible death of a main character. And yet, once the episode was over, internet could only speak of one thing: How could Jaime drown a mere yard from knee-deep water? Why did no one notice this mistake? After all, you don’t need a geologist to know this doesn’t work. You just need to stand in any given river to see that the edges should not be this steep.

00:47 - Well think again, because this river is not only possible from a geological point of view, but its depth can also tell us a lot about the climate of the world of Game of Thrones. Sit comfortably by the fireside, as today we’re going to take a look at the climate changes that Westeros has experienced. But before we dive into the details, it’s important to take a look at the history and geography of the world of Games of Thrones. Even if you’ve never watched this series, chances are you’ve heard or read the phrase “Winter is coming” Because unlike what we know on Earth, the seasons do not follow one another every year in Westeros. Summers can last for many years, while some winters would have lasted for generations.

01:28 - There are several ways to explain such a climate, but perhaps the most reasonable is one that focuses on the way this planet revolves around its sun. On Earth, we know that the alternation of the seasons depends on our orbit around the sun, which is the path we take each year, and the inclination of the axis of rotation of our planet, the axis around which we revolve every day. Because if we often represent our world by placing the North-South axis vertically, this is not really what an observer would see from the Sun. As with a number of planets, the axis of rotation is tilted by about twenty degrees. This way, one hemisphere always receives the Sun’s rays more directly than the opposite hemisphere.

02:07 - The first will therefore experience greater heat, and the second will be plunged into a winter. Six months later, the situation will be reversed, which will result in an alternation between summer and winter each year. But imagine what would happen if the axis of rotation changed its orientation. What if, as a consequence , the same hemisphere was always facing the sun? This hemisphere would receive a lot of heat all year round, while the other would be continually plunged into an endless winter. To test the validity of this model, it would take much more data than we have about the geological history of Westeros.

02:41 - Unfortunately, there has obviously not yet been a Maester Cuvier, Maester Darwin or Maester Agassiz to study the palaeoclimates of this planet. The only data we have are therefore the stories passed down from generation to generation. These alternations between cold and hot periods, were not completely made up by George R. R. Martin. Because between the Middle Ages and the industrial revolution, the world experienced a colder period. This is what we call the Little Ice Age. The temperatures were so cold during this period that some frost fairs were held on the frozen surface of the rivers that flow through major European capitals.

03:51 - With these cooler temperatures, the glaciers grew larger and began to move forward. In Scandinavia, some glaciers are said to have advanced at the rate of several tens of meters per year. In just a few decades, cubic kilometers of solid water had thus filled the valleys. If this sounds impressive, we should also remember that glaciers have to face each year an enemy who tries to slow them down in their advance: summer. After growing during the winter, glaciers have to withstand higher temperatures.

04:19 - Part of the glacier will melt, and it will be able to grow again when temperatures drop. But if the summers are cooler, like those that marked the Little Ice Age, a lesser amount of ice that formed during the winter will melt. When winter returns, some of the ice that had formed the year before remains, and the glacier starts off with a head start. The glacier will grow even more during the winter, and the new summer will not be able to melt all the new ice that has formed. Over the years, the glacier will grow and advance. This is how an ice age begins. Now imagine this phenomenon in Westeros.

04:58 - Winters do not last a few months, but a few years, or even a few decades. And without a summer to melt them, glaciers have no obstacle in their advance. If the glaciers of the Little Ice Age still managed to gain ground despite their summer melt, you can imagine how quickly the glaciers of Westeros would be able to grow. During the winter periods, the seven kingdoms quickly find themselves covered with snow and crossed by glaciers. But when the land is covered with a white color, it does not help the climate to warm up.

05:30 - Unlike dark rocks or asphalt, which will absorb the heat they receive from the sun, white surfaces will reflect sunlight. This characteristic, called albedo, thus prevents part of the sun’s energy from heating the surface of the planet. Temperatures become cooler, which will lead to greater snowfall and larger white surfaces. These snow-covered surfaces will therefore increase albedo, which will eventually cause temperatures to drop. In a world without summer, like the one of Westeros, landscapes could quickly fill up with ice.

06:04 - To study the impact that such a climate would have on rivers, we will have to go back a little further in the history of the Earth. We are therefore leaving the 18th century, and we are heading towards the last ice age that our planet experienced, 20,000 years ago. At that time, the heat received during the summer was not sufficient to melt the ice, and gigantic ice caps had covered Europe and North America. The problem is that the Earth contains a finite amount of water, which is distributed on the surface between lakes, rivers, oceans and glaciers. If a large part of the water is stored in the form of ice, this will lead to a decrease in the amount of water available to fill the other basins, and in particular, the ocean basins.

06:46 - To summarize, evaporation takes water from the oceans, which the clouds then transport to the continents. If the resulting rain remains liquid, it will fill the rivers and return to the oceans. But if it is stored as ice, it will not return to where it came from. After a few thousand years, the sea level will eventually drop and the seaside will shift. And to verify that this phenomenon really took place, just look at the seabed in front of the mouths of french rivers.

07:14 - Let’s look for example at the depth of the Atlantic ocean on the western coast of France. What you see here are areas where the seabed is a bit deeper. These are the traces left by the paleoLoire, the erosion caused by a river flowing here when sea level, which was 120 meters below the one we know today, had shifted the position of the coastline. We can also see the same thing in the English Channel, where the PaleoSeine was flowing. Sometimes, sediment can completely cover the bed of these ancient rivers.

07:45 - This is for example the case of the Gironde river, where seismic waves must be sent toward the seabed in order to be able to analyze the structure of the sediments which filled the old bed of the river. The same phenomenon can also be seen in Brittany, where scientists have been able to reveal, thanks to the thickness of the sediments, the network of an old river that flowed south of Crozon. But if all these rivers were to descend much lower, you can imagine that they had to dig their beds to get there. To verify this, just look at the thickness of the sediments that have settled around rivers. And indeed, whether it’s in the Loire Valley or the Seine, we discover deeper valleys, filled with sediments that are only a few thousand years old.

08:28 - But if those valleys carved in the rocks end up filled with sand and mud, Jaime couldn’t have sunk so deep. He would have simply collapsed in 30 centimeters of water before being charred. We must therefore remember a big difference between our world and that of the Lannisters. Since the end of the Ice Age 11,000 years ago, the level of our oceans has gradually risen. The valleys carved out by the rivers found themselves inundated, which formed a larger area where the river and the sea merge, which is called an estuary.

09:00 - The shape of the coasts can thus tell us a lot about the erosion that sculpted our land during the last ice age. So let’s take a moment to look at what the shores of Westeros look like. One only has to look at the eastern part of the continent to realize that Jaime’s world is not that different from ours. From the wall of ice all the way to Dorne, the sea creeps inland many times, filling the valleys that rivers had carved out when the sea level was lower. These large bays, often used in the series to allow opposing fleets to approach the capital, would not have had the same shape if Westeros had not experienced an Ice Age.

09:40 - But when sea level rises after the Ice Age, when it gets so high that it can fill estuaries, rivers no longer need to carve their way into the rock. They begin to fill up with sediment, and the estuaries will also gradually fill up with sand and mud. But on Westeros, since the long, freezing night that would have lasted for decades, it hasn’t been all springtime. From time to time, winters of a few years disrupt the life of the Westerosi. If the growth of glaciers and the accumulation of snow during our winters do not cause the level of the oceans to vary by more than a few millimeters per year, it would probably be different in a world without summers, where accumulations of snow do not disappear from one year to another.

10:21 - In addition, it should be noted that the oceans contract when they are colder. We can also see how this thermal contraction can create local variations in sea level of several tens of centimeters, as is the case here during the winter in China, or during the Australian winter. During the long winters of Game of Thrones, the oceans would contract, some of the water would remain stored on land, and the maesters could register a small drop in sea level. But how many years would it take to remove the sand and mud that had accumulated in rivers during previous summers? If we can only speculate about the impact of these variations in sea level on river erosion, we can nonetheless look at another way that glaciers have of sculpting the ground. While these expanses of ice can control the level of oceans and rivers, they can also directly alter the landscapes they cover.

11:14 - Because these glaciers hide inside a whole network of liquid water. While this water can come from the gradual melting of the glacier, it can also come from the sudden emptying of a lake that had formed on the surface or inside a cavity in the glacier. The problem is that it is rather complicated for this water to escape from the mass of ice. It will therefore accumulate at the base of the glacier, the pressure will increase, and it will start digging the rocks on which the glacier rested. In this way, water can carve a tunnel under the ice, forming a deep valley with sometimes vertical edges.

11:48 - These tunnel valleys can then be filled with sand, like those found under the German plains, while others, like those under the North Sea, have been able to keep track of the relief that had been dug under the ice that covered this region 20,000 years ago. And it is not only in the oceans that tunnel valleys can maintain their relief. If we look at the great American lakes, these expanses of water left behind by the melting of the gigantic ice cap that covered Canada, we can see a few elongated lakes south of Lake Ontario. In some of these lakes, which can reach over 180 meters of depth, you could stack the Statue of Liberty twice without it protruding above the surface. And if the slopes of these valleys are not always as steep as some exaggerated figures may suggest, as is the case here, they can sometimes show quite a steep drop.

12:38 - Thanks to the sediments that the glaciers had pushed while growing, we know that these lakes are found today where the ice cap left off. Where the water trapped in this expanse of ice escaped by digging into the rock. And if glaciers left such deep valleys on Earth, there is no reason to think it would be any different in the world of Game of Thrones. If a river found one of these valleys in its path, if it borrowed its steep slopes for a while, it would not be surprising to find there a perfect pit for an improvised diving session. The fall of Jaime is ultimately not that surprising.

In a world 13:16 - where the seasons last for decades, winters are bound to leave an indelible mark on landscapes. The accumulation of ice on land, by causing the level of the oceans to fall, will force the rivers to cut their beds deeper to catch up with the displacement of the coastlines. The rivers will dig small canyons in the land, and valleys will develop at their mouths. When the temperatures come back up, the oceans will rise and thus fill these incised valleys, forming the estuaries that we know today. Rivers will flow in the bed they carved and might even flow through valleys that glaciers carved out, by forcing pressurized water to dig into the rock to escape.

13:57 - If Jaime was able to survive the dragon’s breath , he can therefore thank the long winters his ancestors experienced. And these are the same ice ages that we can thank for the awesome battles that the estuaries of Westeros have offered us. If any of your friends complained about this scene in Game of Thrones, feel free to share this episode with them. And if there are any other scenes from movies or series that you’d like to see geologically analyzed, let me know in the comments. I will see you soon, and meanwhile… watch where you step! .