skier nor a tourist, snow and ice didn’t concern me. I thought I was done with the Kingdom of Frost and didn’t even realize that I was still wandering around in the midst of it. I didn’t see that the whole landscape in Norway had been shaped by the ice. The distinctive, world-famous fjords and valleys, the huge erratic boulders you could see in the most peculiar places—all of this was the work of the ice. And I was far from the only person who was blind to it. People had walked around here for hundreds, thousands of years without realizing it. They just took for granted that the landscape was the way it was and didn’t ask why.
Indeed, it wasn’t until the mid-1800s that people learned that the glaciers had carved out these U-shaped valleys, leaving fertile earth in the valley bed. People had no idea that there had once been glaciers here. There was nothing about it in the Bible, which was the most important history book until the 1800s. Most people then believed the world had existed for only 6,000 years. And the term “ice age” was totally unknown.
It took a Danish immigrant to discover that there was something strange about this, something that demanded an explanation. The huge stones that often stood balanced on top of a hill couldn’t have ended up there all by themselves. Stones don’t roll uphill. And the huge, continuous ridges of rock and gravel down in the valley: who or what had created them?
It must have been questions like these that Jens Esmark (1763–1839) pondered during his many journeys around Norway. Esmark was a trained “mineralogist,” as geologists were called in the late 1700s when he arrived in Norway, initially to work in Kongsberg. At that time, it was an important mining town and also had an institution called the Bergverkseminar, known in English as the Kongsberg School of Mines, which is where Esmark taught. After the company in Kongsberg went bankrupt in 1805, Esmark moved to nearby Christiania, modern-day Oslo. There, he became the first professor of mineralogy at Norway’s first university, which opened in 1811.25
While he was living in Kongsberg, Esmark had already managed to travel around and familiarize himself with the Norwegian mountain regions. He was probably the first person to climb mountains like Snøhetta and Gaustatoppen, and he also undertook height measurements of both using barometers, which measure air pressure. This enabled him to prove—to many people’s surprise—that Gaustatoppen, hitherto considered the “roof of Norway,” was not Norway’s highest mountain but was actually lower than Snøhetta.
On his journeys to map the geology of the Norwegian landscape, Esmark traveled to places such as Lysefjorden in western Norway. There, at the end of the lake called Haukalivatnet, lies a terminal moraine, which we now know was deposited by a glacier. Before Esmark proposed this theory in 1823, nobody had guessed that this formation was created by a glacier that had long since disappeared.
Eventually, he discovered similar traces in many places and wrote an article in which he set out his theory that there must once have been glaciers across the whole of Scandinavia, which had created the characteristic formations for which the Norwegian landscape is so famous.
Esmark also had his ideas published in English in 1826 but failed to attract much attention. However, the renowned professor Robert Jameson, who was at one time Darwin’s teacher in Edinburgh, gave lectures about Esmark’s ideas and it is quite possible that they spread further from there. One of Jameson’s contacts was the Swiss natural scientist Louis Agassiz (1807–1873). We have no proof that Agassiz became aware of Esmark’s ice age theory through Jameson, but it is highly unlikely that Jameson would not have told Agassiz about it; Jameson was Agassiz’s English publisher.
At any rate, it was Agassiz who won all the glory for introducing the theory of the ice age, while Esmark vanished into oblivion. That is often the way with science: it isn’t necessarily the person who came up with an idea who wins glory for it but the person who first manages to disseminate it to a wider public—as Agassiz did, initially at a famous lecture in Neuchâtel in 1837. The theory of the ice age made waves in scientific circles and was met with skepticism. Even renowned scientists, including the German naturalist Alexander von Humboldt (who had been Agassiz’s teacher), slaughtered the idea. But the data supporting the theory were impossible to explain any other way.26
Being from Switzerland and very familiar with the Alps, Agassiz had noticed some of the same phenomena Esmark had seen in Norway: for example, the erratic boulders and the moraine ridges. Agassiz had seen how modern-day glaciers could carry such rocks along with them, and how they formed moraines from stones and gravel. He also noticed the striations on the surfaces of the rock, which all went in one and the same direction, as if somebody—or something—had scraped the rock with some vast instrument.
Eventually, Agassiz was able to picture how the ice had covered a much larger area than the small glaciers that still remained up in the mountains. He latched on to a term one of his friends, a half-crazy German botanist called Karl Schimper, had used in a poem in 1837: ice age. Agassiz gathered more proof and in 1840, he was able to publish his revolutionary theory: that large swaths of Europe, and perhaps other parts of the world, had once been covered in ice, and that this could explain many of the landscape formations. As he put it: “In my opinion, the only way to account for all these facts and relate them to known geological phenomena is to assume that . . . the Earth was covered by a large ice sheet that buried the Siberian mammoths and reached as far toward the south as did the phenomenon of erratic boulders.”27
Agassiz was here referring to the mammoths that had created a furor when well-preserved specimens were discovered in the Siberian tundra. The discovery of these mighty frozen creatures helped give his theory credibility. At first, it is true, people thought they were elephants, washed north to Siberia by the flood described in the Old Testament. But the French natural scientist Georges Cuvier (1769–1832) proved mammoths were a separate species, specially adapted to life in the cold Arctic.
In spite of severe opposition—this contradicted the Bible, after all, and predated Darwin’s theory of evolution—Agassiz’s theory was eventually accepted. And now, suddenly, the traces were easy to see and people found them almost everywhere: moraines, erratic boulders, striations, U-shaped valleys, or U-shaped fjords, as in Norway. The same types of traces also appeared in other parts of the world, such as North America and New Zealand. Old stories about how the glaciers had grown or shrunk, previously dismissed as tall tales, were looked at again. Agassiz himself moved to the United States, where he garnered considerable recognition as a scientist and became a professor at Harvard. In his new homeland, he saw many signs that North America had also had an ice age. The great lake that formed when these glaciers melted was named Lake Agassiz.
Aided by numerous ingenious methods, scientists have since discovered that there hasn’t been just one ice age, but many. In the past 800 million years, in particular, Earth has frozen and thawed, frozen and thawed in a cyclical dance. In the past 800,000 years alone, there have been at least nine ice age “episodes.” The first thorough documentation of this was in the 1960s and ’70s, with British scientist Nicholas Shackleton’s analysis of sediments from the ocean bed, together with Danish paleoclimatologist Willi Dansgaard’s ice-core drilling in Greenland. Both made use of the fact that the composition of oxygen isotopes (variants of oxygen with different atomic weights) changes in step with temperature and sea level. On that basis, it was possible to produce time series that showed how the climate had fluctuated in the last ice age periods. Among others, they showed that Earth has spent most of the past million years in ice ages and that it has been much colder than it is in our times. Even though solar radiation has increased, Earth has basically become colder. According to this pattern, we should now actually be on our way back to a new ice age. But because of what we are currently doing to the atmosphere, it is far from certain this will happen.
WHAT CAUSES ICE AGES?
WHY ALL THESE fluctuations, these shifts between cold and hot periods? Isn’t the temperature on Earth primarily determined by solar radiation? And in the 4.5 billion years in which Earth has
