Life below zero: building the Ice Age

As I write this post, parts of the US are digging themselves out of a massive snowstorm. (Locally, of course, the anti-snow bubble was in full effect, and the Tennessee Valley area got only a dusting.) Lots of snow, cold temperatures, and high winds create a blizzard, a major weather event that comes around once every few years.

But our world has gone through extended periods of much colder weather. In fact, we were basically born in one. I’m talking about ice ages. In particular, I’m referring to the Ice Age, the one that ended about 10,000 years ago, as it’s far better known and understood than any of the others throughout the history of the planet.

The very phrase “Ice Age” conjures up images of woolly mammoths lumbering across a frozen tundra, of small bands of humanity struggling to survive, of snow-covered evergreen forests and blue walls of ice. Really, if you think about it, it paints a picturesque landscape as fascinating as it seems inhospitable. In that, it’s no different from Antarctica or the Himalayas or Siberia today…or Mars tomorrow. The Earth of the Ice Age, as a place, is one that fuels the imagination simply because it is so different. But the question I’d like to ask is: is there a story in the Ice Age?

Lands of always winter

To answer that question, we first need to think about what the Ice Age is. A “glaciation event”, to use the technical term, is pretty self-explanatory. Colder global temperatures mean more of the planet’s surface is below freezing (0° Celsius, hence the name of this post), which means water turns to ice. The longer the subzero temps, the longer the ice can stick around. Although the seasons don’t actually change, the effect is a longer and longer winter, complete with all the wintry trappings: snow, frozen ponds and lakes, plant-killing frosts, and so on.

We don’t actually know what causes these glaciation events to start and stop. Some of them last for tens or even hundreds of thousands of years. The worst can cover the whole world in ice, creating a so-called “Snowball Earth” scenario. (While interesting in its own right, that particular outcome doesn’t concern us here. On a snowball world, there’s little potential for surface activity. Life can survive in the deep, unfrozen oceans, but that doesn’t sound too exciting, in my opinion.)

If that weren’t bad enough, an Ice Age can be partially self-sustaining. As the icecaps grow—not just the ones at the poles, but anywhere—the Earth can become more reflective. Higher surface reflectivity means that less heat is absorbed, dropping temperatures further. And that allows the ice to spread, in a feedback loop best served cold.

Living on the edge

But we know life survived the Ice Age. We’re here, after all. The planet-wide extinction event that ended the Pleistocene period came at the end of the glaciation event. So not only can life survive in the time of ice, it can thrive. How?

Well, that’s where the difference between “ice age” and “snowball” comes in. First off, the whole world wasn’t completely frozen over 20,000 years ago. Yes, there were glaciers, and they extended quite far from the poles. (Incidentally, the glaciers that covered the eastern half of America stopped not that far from where I live.) But plenty of ice-free land existed, especially in the tropics. Oh, and guess where humanity came from?

Even in the colder regions, life was possible. We see that today in Alaska, for instance. And the vagaries of climate mean that, strangely enough, that part of the world wasn’t much colder than it is today. So one lead on Ice Age life can be found by studying the polar regions of the present, from polar bears to penguins and Eskimos to explorers.

The changing face

But the world was a different place in the Ice Age, and that was entirely because of the ice. The climate played by different rules. Hundreds of feet of ice covering millions of square miles will do that.

The first thing to note is that the massive ice sheets that covered the higher latitudes function, climatically speaking, just like those at the poles. Cold air is denser than warm air, so it sinks. That creates a high-pressure area that doesn’t really move that much. In temperate regions, high pressure causes clockwise winds along their boundaries, but they tend to have stable interiors.

Anyone who lives in the South knows about the summer ridge that builds every year, sending temperatures soaring to 100°F and causing air-quality and fire danger warnings. For weeks, we suffer in miserable heat and suffocating humidity, with no rain in sight. It’s awful, and it’s the main reason I hate summer. But think of that same situation, changing the temperatures from the nineties Fahrenheit to the twenties. Colder air holds less moisture, so you have a place with dry, stale air and little prospect for relief. In other words, a cold desert.

That’s the case on the ice sheets, and some thinkers extend that to the area around them. Having so much of the Earth’s water locked into near-permanent glaciers means that there will be less precipitation overall, even in the warm tropics. That has knock-on effects in those climates. Rainforests will be smaller, for example, and much of the land will be more like savannas or steppes, like the African lands that gave birth to modern humans.

But there are still prospects for precipitation. The jet stream will move, stray winds will blow. And the borders of the ice sheets will be active. This is for two reasons. First, the glaciers aren’t stationary. They expand and contract with the subtle seasonal and long-term changes in temperature. Second, that’s where the strongest winds will likely be. Receding glaciers can form lakes, and winds can spread the moisture from those lakes. The result? Lake-effect precipitation, whether rain or snow. The lands of ice will be cold and dry, the subtropics warm (or just warmer) and dry, but the boundary between them has the potential to be vibrant, if cool.

Making it work

So we have two general areas of an Ice Age world that can support the wide variety of life necessary for civilization: the warmer, wetter tropics and the cool convergence zones around the bases of the glaciers. If you know history, then you know that those are the places where the first major progress occurred in our early history: the savannas of Africa, the shores of the Mediterranean, the outskirts of Siberia and Beringia.

For people living in the Ice Age, life is tough. Growing seasons are shorter, more because of temperature than sunlight; the first crops weren’t domesticated until after the ice was mostly gone, when more of the world could support agriculture. Staying warm is a priority, and making fire a core part of survival. Clothing reflects the cold: furs, wool, insulation. Housing is a must, if only to have a safe place for a fire and a bed. Society, too, will be shaped by these needs.

But the Ice Age is dynamic. Fixed houses are susceptible to moving or melting glaciers. A small shift in temperature (in either direction) changes the whole landscape. Nomadic bands might be better suited to the periphery of the ice sheets, with the cities at a safe distance.

The long summer

And then the Ice Age comes to an end. Again, there’s no real consensus on why, but it has to happen. We’re proof of that. And when it does happen…

Rising temperatures at the end of a glaciation event are almost literally earth-shattering. The glaciers recede and melt (not completely; we’ve still got a few left over from our last Ice Age, and not just at the poles), leaving destruction in their wake. Sea levels rise, as you’d expect, but they could also sink, as the continents rebound when the weight of the ice is lifted.

The tundra shrinks, squeezing out those plants and animals adapted to it. Conversely, those used to warmer climes now have a vast expanse of fresh, new land. Precipitation begins to increase as ice turns to water and then evaporates. The world just after the Ice Age is probably going to be a swampy one. Eventually, though, things balance out. The world’s climate reaches an island of stability. Except when it doesn’t.

Our last Ice Age ended in fits and starts. Centuries of relative warmth could be wiped out in a geological instant. The last gasp was the Younger Dryas, a cold snap that started around 13,000 years ago and lasted around a tenth of that time. To put that into perspective, if it were ending right now (2016), it would have started around the time of the Merovingians and the Muslim conquest of Spain. But we don’t even know if the Younger Dryas was part of the Ice Age, or if it had another cause. (One hypothesis even claims it was caused by a meteor striking the earth!) Whether it was or wasn’t the dying ember of the Ice Age doesn’t matter much, though; it was close enough that we can treat it as if it were.

In the intervening millennia, our climate has changed demonstrably. This has nothing to do with global warming, whatever you think on that topic. No, I’m talking about the natural changes of a planet leaving a glacial period. We can see the evidence of ancient sea levels and rainfall patterns. The whole Bering Strait was once a land bridge, the Sahara a land of green. And Canada was a frozen wasteland. Okay, some things never change.

All this is to say that the Ice Age doesn’t have to mean mammoths and tundra and hunter-gatherers desperate for survival. It can be a time of creation and advancement, too.

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