Chapter Content
Okay, so like, I had this dream, or, well, it wasn't really a dream, more like a… well, anyway, it reminded me of this poem. It goes: "The bright sun was extinguished, and the stars did wander darkling in the eternal space…" Pretty heavy, right? That's Byron.
So, you know, back then, there was this crazy volcano, Tambora, in Indonesia. Totally blew its top. I mean, we’re talking huge. Nobody alive had ever seen anything like it. It was like, a hundred and fifty times bigger than Mount St. Helens, the one that went off in the US. And, uh, like, the energy of sixty thousand Hiroshima bombs. Imagine!
News, you know, it travelled real slow back then. It took like, seven months for the London Times to even mention it, and even then it was just a short piece. But people *felt* it way before that. All that dust, like, a ton of it, went into the atmosphere, blocking the sun. Made sunsets all weird and dark, which, you know, some artists dug, like this painter, Turner, he painted them. But mostly, it was just…dark. It was like, this really depressing, awful darkness, you know? Gave Byron the inspiration for that poem I started with.
Spring never really showed up that year, and summer was… well, not warm. It was literally called "the year without a summer." Crops failed everywhere. There were famines, diseases... Terrible. People called it "18-hundred-and-froze-to-death." Stuff just wouldn’t grow. Livestock died off 'cause there wasn't enough to feed them. Honestly, a really awful year. And the crazy thing is, globally, the temperature only dropped like, less than one degree Celsius. Just shows you how fragile the whole system is, you know?
But the thing is, even that year wasn't *that* cold, relatively. See, for the two hundred years before that, Europe and North America had been going through what they call a "little ice age." People were having festivals on the frozen Thames River. You could skate on the canals in Holland, all that stuff. So, people were kind of used to the cold, you know? So geologists didn't really realize that they were actually living in a relatively warm period compared to what had been. They didn’t realize that the landscape around them had been shaped by, like, massive glaciers and cold weather that would make any ice festival totally impossible, if that makes sense.
They knew *something* weird had happened, though. You’d find reindeer bones in southern France. Random huge rocks, just sitting where they shouldn’t be. People came up with crazy theories, you know? Like this guy De Luc thought that maybe, like, compressed air in caves had, like, shot those rocks up onto the mountains, like a cork from a toy gun! Total nonsense, but, you know, people were more interested in whether the explanation sounded good than whether it actually, you know, fit reality.
This other geologist, Hallam, said that if Hutton, who was like, the father of geology, had just gone to Switzerland, he would have seen all the evidence, all those weird valleys and the rocks and stuff, that clearly meant glaciers had passed through. But Hutton wasn't a traveler, so...
Even with the limited information Hutton had, he knew a massive flood didn't cause those huge rocks to go up a thousand meters. He pointed out that there's no water in the world that can float rocks. He was like, one of the first to argue for massive glaciation. But nobody really listened. For like, half a century, most scientists were saying the marks on the rocks were just, you know, from carts or even hobnail boots, scraping along the ground. Seriously?
But, the local farmers, they knew better, you know? This Swiss naturalist, Charpentier, was walking with a woodcutter, and they were talking about these random boulders in the fields. And the woodcutter just straight up told him that they came from the Grimsel region, far away. He said that the Grimsel glacier, like, dragged them there, because it used to stretch all the way to Bern!
Charpentier was stoked because he'd already kind of figured that out himself. But when he presented the idea at a scientific meeting, people didn't really buy it. His best friend, this other Swiss naturalist Agassiz, was skeptical at first. But then, eventually, he came around. He was totally on board!
Agassiz, he had been studying, in Paris. Then, he was a professor in Switzerland. A botanist friend of his, Schimper, actually coined the term "ice age." He said that, like, there was a ton of evidence that ice sheets covered not just the Alps, but huge parts of Europe, Asia, and North America. That was a pretty radical idea at the time. He lent his notes to Agassiz, and he later regretted it, because Agassiz basically took the credit, you know? And Charpentier ended up hating his old friend too, which is just like, ugh, the drama. Another friend of Agassiz, Humboldt, said that there were three stages to scientific discovery: First, people deny it's true. Then, they deny it's important. And finally, they credit the wrong person. I mean… he was probably thinking about Agassiz a little bit, when he said that.
Still, Agassiz was all about this. He went everywhere to study glaciers. Climbed mountains. Even if, like, nobody had ever been there before. But everywhere he went, people doubted him, you know? Humboldt told him to stop being so obsessed with glaciers and to go back to studying fish fossils! But Agassiz was, like, totally fixated.
In England, even fewer people agreed with Agassiz, because, well, most English naturalists had never even *seen* a glacier. They couldn’t really grasp the power of ice. This one guy, Murchison, sarcastically asked if they were really saying that the scratches and grooves on rocks were just from glaciers! He was obviously thinking that the rocks were just covered with a light layer of ice. He never really believed in those "glacier maniac" geologists. Hopkins, who was the head of the Geological Society, said that the idea that glaciers could move rocks was, like, "mechanically absurd" and not even worth the Society's attention.
Agassiz didn't give up. He kept, like, running around, trying to convince people. In 1840, he presented a paper at a meeting and this other geologist, Lyell, just, like, totally ripped him apart. A year later, the Geological Society of Edinburgh said that Agassiz *might* have a few good points, but that his theory definitely didn't apply to Scotland.
Lyell eventually changed his mind, though. He was walking near his house in Scotland and suddenly realized that this pile of rocks that he had seen a bunch of times, called a moraine, could only have been put there by a glacier. Even after, like, privately, he believed the ice age theory, but he didn't have the guts to publicly support it! Tough time for Agassiz. His marriage fell apart, Schimper accused him of stealing his work, Charpentier wouldn’t talk to him, and Lyell, who was pretty much the biggest geologist at the time, only gave him lukewarm support.
But then, in 1846, Agassiz went to America to give lectures, and he finally got the recognition he deserved. Harvard gave him a professorship and built him this amazing museum. He settled in New England, which definitely helped, because those long winters made people, like, more open to the idea of long cold periods. Then, like, six years later, Agassiz made his first scientific expedition to Greenland. That also helped. They found that the whole island was covered in ice, just like Agassiz had said ancient ice sheets must have been. People started to actually believe him. But, Agassiz couldn't actually explain *why* ice ages happened.
But, help came from an unexpected place. In the 1860s, British newspapers started publishing articles by this guy, Croll, from the University of Glasgow. They were about like, fluid mechanics, electricity, all sorts of stuff. One of them suggested that changes in the Earth's orbit might cause ice ages. It was published in the Philosophical Magazine and got, like, a ton of praise. But then people found out that Croll wasn't, like, a researcher at the university, just a staff member!
Croll was born into a poor family. He quit school when he was 13 and worked a bunch of jobs, carpenter, insurance salesman, you name it. Then he got a job as a janitor at the University of Glasgow. He convinced his brother to help him with some of his work so he could spend quiet evenings in the university library, teaching himself physics, math, astronomy, all these new subjects. Eventually, he started writing papers, focusing on the Earth's movement and how it affects the climate.
Croll was the first one to suggest that the Earth's orbit changes, from being more elliptical to being more circular, and back again. These cycles could be the cause of ice ages coming and going. Nobody had ever explained weather changes from an astronomical point of view before. Thanks to Croll, people in Britain started to accept the idea that parts of the Earth used to be covered in glaciers. Croll got recognition for his talent. He got a job with the Geological Survey of Scotland, got a bunch of awards, all that.
Unfortunately, right when people in Europe were finally starting to accept Agassiz's theory, he was out doing fieldwork in unexplored parts of the Americas. Everywhere he went, even near the equator, he kept finding evidence of glaciers. He eventually became convinced that ice had covered the entire Earth, destroying all the life God had created. The evidence he used just, like, didn't support that idea. Still, he got really famous in the US, so much so that when he died in 1873, Harvard had to hire three people to replace him.
But Agassiz's theory didn't stay popular for long. Like, less than ten years after he died, the new head of the geology department at Harvard wrote that "the so-called ice age... which a few years since was the delight of every glacial geologist, is now unhesitatingly rejected."
Part of the problem was that Croll’s calculations said that the last ice age happened eight thousand years ago, but geological evidence was increasingly showing that the Earth had gone through something pretty crazy way more recently than that. If you couldn’t explain what caused the ice age, the whole theory fell apart.
But then, this Serbian scientist named Milankovitch showed up. He didn't even study astronomy or anything; he was a mechanical engineer. But he suddenly got interested in the problem in the early twentieth century. He realized that the problem with Croll's theory wasn't that it was wrong, but that it was too simple.
The Earth, as it travels through space, it’s not just the shape of its orbit that changes, but also the angle it's pointing towards the sun, you know, its tilt and stuff. All of that affects how much sunlight hits different parts of the Earth. Specifically, the Earth goes through three different position changes over long periods of time. Milankovitch thought that maybe those changes had something to do with ice ages. Problem was, those cycles are all different lengths. Some are like twenty thousand years, some are forty thousand, some are a hundred thousand, so you have to figure out how they all line up over a really long time. Milankovitch had to calculate how much sunlight hit every latitude of the Earth in every season for a million years!
Luckily, that kind of complicated work was perfect for Milankovitch. For the next twenty years, he just kept calculating, even on vacation, with just a pencil and a slide rule. That’s, like, something that could be done with a computer in a day or two, today. He had to do the calculations in his spare time, until 1914. That’s when World War One broke out, and he was arrested because he was a reservist in the Serbian army. He spent most of the next four years under house arrest in Budapest, but it was, like, a pretty easy house arrest, you know? He only had to report to the police once a week, and the rest of the time he was working hard in the library of the Hungarian Academy of Sciences. He was, like, probably the happiest prisoner of war ever.
The result of all that hard work was a book published in 1930, called "Mathematical Climatology and the Astronomical Theory of Climate Changes." Milankovitch was right; ice ages are definitely connected to Earth's movements. But he, like most people, thought that long, cold winters caused the ice ages. It was this Russian-German meteorologist, Köppen, who figured out that it was actually more complicated and scarier than that.
Köppen realized that it's actually cool summers that cause ice ages, not cold winters. If the summers in an area are really cool, the sunlight bounces off the ground, making it even colder, and causing more snow to fall. Eventually, the snow starts to stick around permanently. As the snow turns to ice, the whole area gets colder and colder. It doesn’t really matter how much snow falls, but more that, how much snow *doesn’t* melt. An ice age starts with a summer that's just a little too cool, that reflects heat, which makes things colder. The ice starts to move, and then bam, you have an ice age.
In the 1950s, the technology wasn't good enough to compare the data we had on ice ages with Milankovitch's exact calculations. So people started to doubt Milankovitch and his calculations. By the time he died in 1958, he hadn't been able to prove that his cycles were correct. In the words of one historian, "you would need, then, to look hard to find a geologist or meteorologist who considered the calculations anything more than an antique." It wasn't until the 1970s, when the potassium-argon dating methods improved, that scientists could finally show that Milankovitch was right.
Milankovitch cycles alone aren't enough to explain ice age cycles. Lots of other factors have to be considered. The distribution of the continents, the presence of landmasses at the poles. But we don't know everything about all of it. They say that if you moved North America, Eurasia, and Greenland five hundred kilometers further north, we’d be in a permanent ice age. Sounds like we're pretty lucky with all the good weather we have now. And we don't really know anything about the cycles of those warmer periods inside the ice age, called interglacial periods. The whole history of human civilization, agriculture, cities, math, science, has happened during this unusually nice period. The last few interglacial periods only lasted eight thousand years. And we're, like, already at ten thousand.
We're still technically in an ice age, it’s just a smaller one, although not as small as a lot of people think. During the last peak of the ice age, like, twenty thousand years ago, about thirty percent of the land surface on Earth was covered in ice. And even now, ten percent of the land is covered with ice. And, like, fourteen percent of the land is permafrost. Three-quarters of the Earth’s freshwater is frozen. There are ice caps at both poles. That's actually pretty unusual for the Earth, historically. So much snow in the winter, permanent ice caps even in places like New Zealand. We're so used to all of that, but it's really rare in Earth's history.
For most of Earth’s history, it’s been much warmer, no permanent glaciers anywhere. The current ice age, really an ice age *era*, started about forty million years ago, going from really intense to not so intense. We live in one of those not so intense periods. New ice ages always wipe out the evidence of old ice ages, so the further back you go, the less complete the picture is. But it seems like we've had at least seventeen major ice ages in the last two and a half million years. All while early humans and then modern humans were running around. The usual suspects for causing the current ice age are the rising of the Himalayas and the formation of the Isthmus of Panama. The Himalayas messed up the air flow, and Panama messed up the ocean currents. India, which used to be an island, crashed into Asia, raising the Himalayas and the Tibetan plateau behind it. That made the climate colder and changed the winds, blowing them north and making it easier for North America to be cold. Then, about five million years ago, the Panama region rose up out of the sea and connected North and South America, which changed the flow of warm water between the Pacific and Atlantic. All of that made Africa drier, which forced the apes down from the trees to find new ways of living in the savannah.
Anyway, it looks like we're gonna be stuck in this long ice age for a while, with the oceans and continents where they are. According to McPhee, we've got about fifty more ice ages to go, each lasting about a hundred thousand years, before we get to hope for a really long thaw.
Fifty million years ago, Earth didn’t have any regular ice ages. But once they did show up on Earth, their scale and duration has been shocking. The first big one was about two point two billion years ago, followed by a billion years or so of warmth. The ice age after that was even bigger. Some scientists even use terms like "Snowball Earth" or "super-ice age" to describe it.
"Snowball" really doesn’t capture how awful it must have been, though. The theory is that, with a reduction in sunlight of about six percent, Earth didn't make or keep heat very well. Earth became like Antarctica, but everywhere, and the temperature dropped by 45 degrees Celsius. The entire Earth's surface froze solid, with oceans up to 800 meters thick at the poles and tens of meters thick in the tropics.
There’s a big problem, though. Geologically, it looks like the entire Earth was covered in ice, even the equator. But biologically, it’s pretty clear that there had to be some unfrozen water somewhere. Cyanobacteria survived and continued doing photosynthesis. You need sunlight for photosynthesis, but light fades pretty quickly through ice, and you can't see anything a few meters down. Maybe some water was unfrozen, maybe some ice was translucent.
If Earth really was frozen over, how did it get warm again? Tough question. A frozen planet would stay frozen because it would bounce too much heat back into space. The answer seems to be magma from inside Earth. We may have to thank plate tectonics, again. Volcanoes pierced the ice sheet, releasing heat and gases that melted the ice and changed the atmosphere. That really cold period ended with the Cambrian Explosion, which was, like, spring for all life. Of course, that spring wasn’t always calm and sunny because as Earth warmed, it went through the most extreme weather ever. Intense hurricanes created waves as high as skyscrapers, and there was incredibly intense rainfall everywhere.
Worms, clams, and other life attached to deep-sea vents probably went on like nothing happened. But all other life on Earth probably came close to extinction. This period of time is extremely remote and not well understood.
Compared to Snowball Earth, the recent ice ages seem pretty small. But still really big by any modern standard. The Wisconsin ice sheet, which covered Europe and North America, was up to three kilometers thick in some places, and it was moving at a rate of 120 meters a year. Even at its edge, it was nearly 800 meters thick. What a sight! Imagine standing at the foot of a wall of ice that high, with millions of square kilometers of nothing but ice behind it, just a few ice peaks in the distance. Whole chunks of land sank under the weight of the ice sheets, and they still haven’t rebounded, even after the ice melted twelve thousand years ago. As the ice sheets moved slowly, they not only pushed around rocks and moraines, but whole chunks of land. Is it any wonder that pre-Agassiz geologists had trouble comprehending that power of the ice?
If the ice sheets came back, we wouldn’t have any way to stop them. There was an earthquake in Prince William Sound, Alaska, the biggest earthquake ever recorded in North America, magnitude 9.2. The ground rose six meters. The earthquake was so strong that ponds in Texas sloshed their water over their banks. But what effect did this incredible tremor have on the glaciers of Prince William Sound? None. The glaciers just kept moving.
For a long time, we thought Earth gradually went into and out of ice ages, over periods of hundreds of thousands of years. But now we know that’s not really the case. Measurements from ice cores in Greenland gave us a detailed record of Earth’s climate for over one hundred thousand years. It wasn't good news. The records showed that the recent Earth has not been the calm place we thought it was. Instead, the climate has jumped wildly between warm and cold.
About twelve thousand years ago, Earth was coming out of the last major ice age. The climate started warming, and it warmed quickly. But then, suddenly, it plunged back into a period of extreme cold for about a thousand years. That period is called the Younger Dryas, named after this arctic plant that was one of the first to grow back after the glaciers retreated. As that thousand-year period of cold ended, the average temperature suddenly rose again, four degrees Celsius in twenty years! That doesn’t sound like much, but it’s enough to change the climate of Scandinavia to the climate of the Mediterranean in just two decades. The changes were even more dramatic in some places. Ice cores in Greenland show that the temperature there changed by eight degrees Celsius in ten years. Those shifts changed the pattern of rainfall and what could grow there. In the past, when there weren't many people, that would have been unsettling. But the consequences would be almost unimaginable today.
The scariest thing is that we don't know, really don't know, what caused Earth's temperature to change so quickly. There is no known external force that could change Earth's temperature so dramatically and so often, like the ice cores show. It seems like there's some kind of huge feedback loop going on. It could be related to disturbances in the normal circulation of the oceans and ocean currents. But we have a lot more to learn.
One theory is that, at the start of the Younger Dryas, a bunch of glacial meltwater poured into the ocean, lowering the salt content of the seawater, which then made the Gulf Stream turn south. Without the heat from the Gulf Stream, the climate in northern latitudes went back into the deep freeze. But that doesn’t explain why, when the Earth warmed again a thousand years later, the Gulf Stream didn't just turn back. Instead, we entered this unusually stable period called the Holocene, the period we live in today.
There's no reason to think that this period of stable climate will last much longer. In fact, some experts think that our climate is already getting worse. You'd naturally think that global warming would make it harder for Earth to go back to a glacial state. But, that also means you're "least willing to do is to actively monitor it across a wide range." Some people even think that the rising temperature might actually *trigger* the start of an ice age. It sounds weird at first, but it makes sense. A slight rise in temperature would cause more evaporation, thicker clouds, and more snowfall at higher latitudes. So global warming might actually make parts of North America and northern Europe colder. It's logical, though it's contradictory.
Climate is the result of so many different things. Rising and falling levels of carbon dioxide, continental drift, the activity of the sun, Milankovitch cycles. Trying to understand the past is as hard as trying to predict the future. We don't understand so many things. Like, Antarctica drifted over the South Pole but wasn't covered in ice for at least twenty million years. It was covered in vegetation. Seems impossible.
Even more incredibly, there are some known habitats of late dinosaurs. A British geologist, Stephen Trulill, found that forests within ten degrees of the Arctic were the home of large animals, including Tyrannosaurus rex. "It’s bewildering," he wrote, "given that these high latitudes would have experienced three months of darkness each year." Even more than that, there's now evidence that those high latitudes had cold winters, too. Oxygen isotope studies showed that the climate in Fairbanks, Alaska, was the same in the late Cretaceous period as it is now. What were T. rex doing there? Either they migrated long distances seasonally or they spent long periods in the dark, snowy cold. In Australia, which used to be closer to Antarctica, there was nowhere warm to retreat to. How did the dinosaurs manage to survive in those environments? We can only guess.
One thing to keep in mind is that, if the ice sheets start to form again, there'll be a lot more water to work with this time around. The Great Lakes, Hudson Bay, all the countless lakes in Canada, they didn't exist and feed the last ice age. They were created by it.
On the other hand, the next stage in our history will probably involve a lot of melting ice, not a lot of forming ice. If all the ice sheets melted, sea levels would rise sixty meters, and all the coastal cities in the world would be underwater. More likely, at least in the short term, the West Antarctic ice sheet will collapse. Over the last fifty years, the temperature of the water around Antarctica has risen by two and a half degrees Celsius, and ice shelf collapse has greatly accelerated. The geology of the area makes a large-scale collapse more likely. If that happens, global sea levels will rise by an average of, quickly, four and a half to six meters.
We don't know whether the future will be extremely cold or extremely hot. But we know that we're living on the edge.
By the way, ice ages aren't all bad in the long run. Glaciers grind up rocks, leaving behind fertile soil. They carve out freshwater lakes that support a ton of life. They move plants and animals around, populating the Earth. To decide the fate of people on any continent, you only have to ask that continent one question: "Did you have a decent ice age?"