The Last Two Times the World Warmed, Pt 1.
Lessons about climate change from two times when things were even more extreme.
Hot Flashes of the Human Race?
The temperature of our planet has varied a lot over its 4.5 billion year existence. 650 million years ago it may have been frozen solid. About 65 million years ago it was so hot there was no frost even in winter at the poles.
These temperature changes are driven partly by regular fluctuations in the earth’s orbit every 100,000 years and in the earth’s tilt every 41,000 years, and partly by seesaw variations in the sun’s output, and partly by very irregular events like volcanic eruptions, asteroid impacts, or—lately—human industrial civilization.
By “human industrial civilization” we mean civilization based on burning fossil fuels—coal, natural gas, and oil—and by lately we mean the last two hundred years. Humans have always impacted the climate (as do all living things1) and humans even burned some coal and natural gas in earlier centuries,2 but during the industrial revolution fossil fuel use really took off, which drastically increased world population, which in turn further increased fossil fuel use, and so on, raising the earth’s temperature a lot in a short span. It’s estimated global temperatures are about 1-2°C higher than they would have been had we not taken up with the coal, natural gas, and oil.3 And we’re just getting started! At current rates we’ll probably add another 1-1.5°C by 2050 AD, and potentially another 1-2.5°C on top of that by 2100 AD.
Even if fossil fuel use were to stop today we’ve already set in motion feedback loops that will continue to increase temperatures.4 So educated guesses (and that’s all they are) give us temperatures by 2200 AD of maybe 3-6°C higher than today. By that time—if not long before—affordable fossil fuels will be rare enough for temperatures and history to take a radically different turn, but if you’re keeping score it all adds up to industrial civilization over the course of 1800 to 2200 AD driving up global temperatures by something like 5-8°C.5 Such a jump naturally has a lot of people worried.
Should they be?
Of course people should feel whatever they feel! Worry if you’re worried! Don’t worry if you’re not worried!
The truth is no one knows what will happen. It’s possible there are natural feedback loops we don’t know about that will kick in to slow, stop, or even reverse the heating! It’s also possible there are natural feedback loops that we don’t know about that will kick in and create a runaway temperature increase that kills us all, along with other large mammals, or at least ends civilization! But possible doesn’t mean likely. A 3-6°C increase by 2200 likely won’t kill off our species, or end civilization, although it almost certainly will end our particular version of civilization.
How do we know all this? Because humans have been through worse. Twice. And not that long ago.
Welcome to the Bølling–Allerød
The Bølling–Allerød is what scientists call the period from 14,700 years ago until about 12,900 years ago. Bølling and Allerød are names of places in Denmark where evidence of past climate change were found. The lines through the o’s are not because the scientists read too many fantasy novels, but because they’re Danish, and the Danish insist on having their own weird letters. Officially, the period is the “Bølling–Allerød Interstadial,” with “interstadial” meaning a warmer period between two cold periods. But we’re going to just stick with Bølling–Allerød and know what we mean.
Ice ages have been coming and going every 100,000 years for the whole two million years humans of one kind or another have walked the earth.6 The most recent ice age peaked about 18,000 years ago. Then century by century, millennia by millennia, the ice retreated, sea levels rose, temperatures began warming, rainfall began increasing—with ups and downs but overall in a fairly steady direction. Then suddenly 14,700 years ago temperatures shot up.7
By a lot.
In the Northern Hemisphere by as much as 9-10°C in only fifty years.
That’s 16-18°Fahrenheit in only five decades. Which is ten times the rate of modern global warming. Imagine Charlottesville, Virginia when you are a kid feeling like Orlando, Florida when you’re old. Boston becomes Savannah. London in a few decades feels like a city on the Mediterranean. Conditions in Northern Europe went from bitter cold to temperate in one lifetime. Tundra became forests. And as we’ll see deserts farther south—because warmer air generally means wetter air—became lush grassland.
But temperatures didn’t stay high for long. In a few decades they started to fall, not as sharply as it had risen, but fairly sharply and continuously, and worst of all (for humans) it kept dropping. Temperatures fell past the bitter cold level the Bølling–Allerød began with and bottomed out at hellishly cold—ice age cold—level around 12,900 years ago, a period called the Younger Dryas, where temperatures were something like 25°C lower than today.8 Over a thousand years Charlottesville feels like Minneapolis, and Massachusetts feels like Greenland.
Then they shot up again. But we’ll visit that next time.
Why Do Temperatures Rise?
Why the sudden spike? After all, those changes in the earth’s tilt and orbit are slow, steady, and predictable. What could make temperatures in less than a century rise so fast? Even with all our greenhouse gas dumping temperatures aren’t climbing anywhere close to that today.
Nobody knows, but the most popular culprit seems to be the Gulf Stream.9 Today the Gulf Stream brings warm water up from the Caribbean across the North Atlantic to Northern Europe, which is why Scotland is warmer than parts of Labrador at the same latitude. The theory is that the Bølling–Allerød spike came from the first appearance of the Gulf Stream, or the first appearance in a long time. Maybe the Gulf Stream cuts on and off. Anyway, according to mathematical models, the Gulf Streams appearance could warm the Northern hemisphere that quickly.10
There are other theories including volcanoes and asteroids, and the ever-popular multiple causes at once. All that is above my pay grade, but one possible cause that I do want to address is the cause we’re experiencing now: Is it possible the Bølling–Allerød spike was caused by anthropomorphic global warming by some previous industrial civilization?
Sadly, so far as such things can be known, we know that there wasn’t an industrial civilization of any size during the Bølling–Allerød. We’ll get into how we know that, but let’s acknowledge that it would have been cool if there had been, and what’s more surprising to me, is that, so far as such things can be known, there could have been. So how could there have been, how do we know there wasn’t, what were humans doing instead, and what does this mean for humans today?
How We Know There Wasn’t
The word civilization brings to mind monumental stone architecture, domesticated plants, writing, dense settlements, priests and kings, and metallurgy. But much of that is just bells and whistles. The Maya, Inca, and Aztecs didn’t cast bronze or forged iron at all. The Inca didn’t have writing.11 Many civilizations used far more wood and earth than stone, while many clearly uncivilized people had priests and kings and built stone monuments.
But metallurgy is necessary for industrial civilization. Without forging or casting boilers and machines there’s no way to harness the productive energy of fossil fuels
Here at Blame Cannon industrial civilization will mean (as I said above) civilizations that make extensive use of fossil fuels—coal, oil, and natural gas, and civilization will mean cultures with domesticated plants, urban settlements (towns or cities), and a complex division of labor.12
We can’t know for sure if there was a division of labor 14,000 years ago, but we can say if there was extensive metallurgy or plant domestication because both leave clear evidence. Domesticated plants are physically different from their wild ancestors. Their structure is different, their pollen is different. Plant and metallurgy leave traces in the atmosphere that can be later found and identified in ice cores in the arctic. Because of this scientists know that there was no substantial amount of plant domestication and no substantial amount of metalworking during the Bølling–Allerød.
Sure, theoretically there might have been a city or two on some coast that later was destroyed by floods, maybe even an industrial city or two, tucked away in a hidden valley or on distant island manufacturing metal tools and growing domesticated plants, but a city or two wouldn’t impact the climate enough to cause a temperature spike ten times the rate of modern global warming.13 Other science fiction ideas like a massive comet or a nuclear war caused by aliens would also leave clear traces in the ice.
So no lost industrial civilization in the last 15,000 years, and that sadly is almost certainly true for the entire 2 million years of humans roaming the earth. Certainly no extensive metallurgy or fossil fuel use, and almost certainly no plant domestication.14
Why not?
How We Know There Could Have Been
All existing humans are of the species homo sapiens which has been around for about 300,000 years. Those older homo sapiens were anatomically the same as us15 so there’s no anatomical reason why civilization, couldn’t have appeared 20,000 or 50,000 or 100,000, or even 300,000 years ago.
Or even further back.
We assume homo sapiens are the most amazing and important humans, since they’re us, but if an alien were to look over the history of our world and pinpoint what humans mattered most, changed most, and accomplished most, they probably wouldn’t say homo sapiens; they’d probably say homo erectus.16
Homo erectus was the first true world-class human. There were species of the genus homo before that—all in Africa as far as we know—but they were mostly scarce scavenging creatures that would have seemed more like upright walking bonobos than us. Then about 2 million years ago homo erectus appeared.
Homo erectus stood taller, had big brains, and migrated across most of the planet in foraging bands, hunting and gathering during the day, sitting around campfires together at night, making sophisticated specialized stone tools, and speaking some sort of language. Basically every known human species since has followed their mold: Foraging bands of 10-40 individuals in multiple families hunting and gathering during the day, sitting around the campfire at night, caring for the sick, sharing food, living in huts or caves, making and using tools of stone, bone, and wood. Homo erectus did it first, and homo neanderthalensis, homo denisova, and until very recently homo sapiens are just copycats.
How smart were homo erectus? Smart enough! The brain size of homo erectus groups varied a lot from place to place depending on conditions. Homo erectus populations in one area might have been dumber than a bag of wet hammers and in another area as smart as we are. Some of the larger homo erectus skulls found were not far off ranges of modern homo sapiens.
By 250,000 years ago homo erectus had diversified into several—perhaps more than several—different species including us. Your racist friend who imagines the earth as having radically different types of humans of differing intelligence and abilities would have probably loved to be around then. Sort of like the Lord of the Rings with elves, dwarfs, and men, except no one was magical and everyone ate a lot of bone marrow. We do know we, homo sapiens, interbred—or should we say intermarried?—with these other humans, and whether by war, birth, or disease—we don’t know why—by 20,000 ago we were the only human left.
While the cultural output of homo sapiens—stone tools, art, railroads, and moon rockets—eventually is far more impressive than other humans, we didn’t really start that way. Neanderthals were as impressive as contemporary homo sapiens.
My point is not only could homo sapiens theoretically have come up with civilization tens of thousands or hundreds of thousands of years before we did, there’s certainly no reason why Neanderthals or Denisovans couldn’t have come up with civilization hundreds of thousands of years earlier, and frankly there’s no anatomical reason why even grandpa homo erectus himself couldn’t have come up with civilization a million years ago.17
In an earlier version of this post I talked the problems of civilization and why many hunter-gatherers could be considered—and would have considered themselves—better off. But I’ve cut that. I want to talk about the early transitions to farming, so we can double back and see why many humans, be they Neanderthal, Denisovans, homo erectus, or earlier versions of us, would have opted out.
What Was There Instead
To see what humans actually did in that rapidly warming early phase of the Bølling-Allerød let’s visit the people archeologists call the Natufians.18
The Natufians lived in what is now Palestine and Israel with a branch stretching up into what is now Syria. The Middle East at the time was becoming warmer and wetter due to the temperature spike so that deserts were becoming grasslands and grasslands forests. At first glance Natufian live much like their hunter-gatherer predecessors, those small egalitarian groups in tents and huts with fire and stone tools that homo erectus had pioneered migrating out of Africa—with the jewelry, figurines, bows, and ritual burials that had been added by other humans in the epochs since.
But three things are unusual:
First, some of the villages seem to be not migratory camps but permanent villages. There are other sites that seem permanent or fairly permanent in prehistory, but they aren’t common. The Natufians are placing their settlements in strategic locations—where woodlands meet forest steppes—so they can gather food from different nearby ecological niches. And they are along the migratory paths of gazelle herds, so like salmon are fished swimming up river during spawning season, the gazelles can be hunted for food and hides. Again, humans may have had permanent or semi-permanent camps in times and places where circumstances allowed since homo erectus, but it has been the exception and not the rule.
Second, the Natufians are making and using the first known stone sickles. Sickles are sharp curved hooks used for cutting grains and other grasses. They not part of the earlier paleolithic tool kit. Other humans are known to have used mortars and pestles to crush wild plants for food or dye, but the Natufians pioneer the sickle. I would invite you to abandon any “brilliant invention” view of this; the existence of sickles is not evidence of a super genius who realized that grains could be eaten or grasses used. Grains were always eaten, grasses always used, but the sickles are evidence that humans were now reaping enough grains and/or other grasses to want a new tool. (Stone axes aren’t very useful for reaping.)
This fits with evidence the Natufians were planting and tending wild plants. These are not domesticated plants, which are different species. Earlier people augmented and altered native plant populations in all sorts of ways, including clearing brush, burning clearings, and planting grains. But not enough to need sickles.
Third, the Natufians had domesticated dogs.
How did wild plants become domestic plants and where did the dogs come from? And what does all this foretell for our own climate future?
Patience friends! Next time we’ll delve into those questions, watch the Natufian world fall apart and rise again, and see what the Younger Dryas has in store.
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There are theories that since about 12,000 years ago humans may have been impacting the climate more than most animals. We’ll take up local prof William Ruddiman’s work in future posts.
Great Britain was burning a fair amount of coal a hundred years before anyone else, and London was burning a fair amount of coal a hundred years before the rest of the British Isles.
1°C is 1.8°F by the way. Our impact on the climate may have been more than that from the beginning of agriculture. See #1 above.
For instance higher temperatures melt permafrost which release methane which further raises temperatures. Melting polar ice reduces reflectivity which allows the planet to absorb more heat.
That’s 12°-14°Fahrenheit.
There was a fad when I was a kid to fear an impending ice age. It was first postulated in 1958, but the pouplar version I remember is Leonard Nimoy’s voice on In Search Of narrating the late 1970s version which imagined the next ice age just around the corner. That’s the program where I also learned about pyramid power, the Loch Ness Monster, Bigfoot, Atlantis, and biorhythms—though biorhythms were popular enough with rationalist types that I think I remember seeing a biorhythm chart on the box of my brother’s first Texas Instrument electronic calendar. Anyway, the next ice age is about 80,000 years away, so it’s probably not worth losing sleep over.
That 14,700 year-ago spike marks the official beginning of the Bølling–Allerød.
The Younger Dryas is named after little flowers found in arctic conditions and therefore used by archeologists to date sites. There was an “Older Dryas” between the Bølling and Allerød parts of the Bølling–Allerød Interstadial, and an “Oldest Dryas” just before the Bølling-Allerød started. One reads a lot more about the Younger Dryas than the Bølling-Allerød, and I honestly wonder if it that’s because of discomfort with those Os with the lines through them. Anyway, the Younger Dryas, the Bølling-Allerød (including the Older Dryas), the Oldest Dryas, and the entire ice age preceeding it are part of the Pleistocene Epoch. The end of the Younger Dryas will begin the Holocene Epoch, our own time.
The Gulf Stream is part of the Atlantic Meridional Overturning Circulation (AMOC) and it’s collapse would disrupt the rest of the AMOC, but mostly people nowadays says AMOC instead of Gulf Stream to prove their graduate school tuition wasn’t wasted.
As I understand it, that would warm up Europe fast, and one of the theories of that sudden chilling after the sudden rise is that the new Gulf Stream warmed the North enough to melt enough ice to diminish the Gulf Stream and bring back the cold. Ironically current global warming could melt enough of the arctic ice to choke off the Gulf Stream and lead Europe into a colder future, while the rest of the planet is warming. It’s all interesting stuff.
The Inca as befitting a huge bureaucratic empire did keep records, but they used knotted strings called quipu.
The oldest civilization is usually described as the Sumerians and dated about 6000 years ago. Defining civilization (as I have) as urban settlements with a division of labor and farming, there are older candidates. We’ll get to those.
A lot of this applies to ideas like those espoused in Graham Hancock’s Ancient Apocalypse. As I understand it (never saw the show) he speculates that during the last ice age there was some sort of “worldwide advanced civilization” which I assume means agriculture and metallurgy. That’s an interesting idea and as we’ll see it might have been true, but sadly it isn’t. Agriculture and metallurgy on a large enough scale for a worldwide civilization would leave trace residue in Greenland ice.
Theoretically, if ancient humans domesticated plants that we don’t know about scientists might miss the pollen. But that makes some assumptions about plant domestication that we’ll examine as we go along.
Except they were probably a little smarter. Modern agricultural civilized homo sapiens brains (us) are about 12.7% smaller than homo sapiens brains 100,000 years ago. No one knows why but it is a general pattern of domesticated animals. Dogs have smaller brains than wolves, pigs have smaller brains than boars, domesticated turkeys have smaller brains than while turkeys.
Homo erectus is sometimes used only for the Asian descendants of what an African ancestor called homo egaster, but keep reading to get to my opinion on the overemphasis on species rather than genus.
Average homo sapiens brains are actually a bit smaller than Neanderthal brains. Homo erectus brains are smaller on average but there’s a very wide range (600-1250cc) so their ceiling isn’t far out of the modern range. But remember the note above that brain size and/or intelligence is not what created civilization.