Will Steffen – TRANSCRIPT
Thanks very much, Steve. For those of you who are expecting a talk on climate change, actually thankfully, you won’t get it.
I’m going to talk about this rather broader context, broader term which puts climate change in a much broader context. That’s the term of “Anthropocene.” Now, for those of you who studied Geology or even watched Hollywood films, you know that geologists like to look at earth history in terms of periods, eras, or epochs, or something. You’ve probably heard of the Pleistocene, many of you. Those of you who have seen the famous Hollywood film certainly know the Jurassic era, Jurassic Park, but there’s a group of us now who are proposing that the earth has actually entered a new epoch at least, perhaps even a new era which is a more substantive term, and that is the Anthropocene.
As the name indicates, Anthropo refers to us. It refers to human beings. Unlike the previous eras in earth’s history which were marked by meteorite strikes, big changes, for example, in plate tectonics or something like this, this is a biological species, ourselves. We are pushing the planet into a new and perhaps, somewhat frightening geological, as well as biological era. Let’s get started with what the Anthropocene actually means.
I really like to show this graph up here. This is some data taken from an ice core in Antarctica. The famous Vostok Ice Core. That’s a Russian station by the name of it but many people don’t know, this ice core comes from Australian territory. This is from the 42% of Antarctica which we claim.
Now, this particular record goes back nearly half-a-million years. The red line in the middle is a proxy for temperature. How temperature changes through the time. The top graph, the blue one, is the famous greenhouse gas that we’re all concerned about, the carbon dioxide. The bottom line is methane.
The important thing is entire human history is encompassed in this ice core. Fully modern humans, Homo sapiens, evolved around 250,000 years ago. You see that in the middle, we evolved in Africa. Now, for well over 90% of our time on the planet, you see that stretched out, we are hunter and gatherers only. Our genetic code is wired for hunting, and gathering, and living in small groups of up to 200 or 300 people.
We live in a quite different world. The beginning of agriculture only occurred at the very end of the record at a warm period. Notice how the ethoxylates in a beautiful rhythmic pattern, much likely human heartbeat between long cold periods and short warm periods, but the present one period is unusually long – I’ll get to that in a moment – which means that it’s given us a bit of time to break out of the hunter and gatherer mole. It’s only during this last 10,000 years that we’ve had agriculture and so on. Let’s look at that in a little bit more detail.
This is another ice core, and this comes from the opposite end of the planet. That other one was down here in the south in Antarctica. This one comes from Greenland, not far from the North Pole. It’s actually a much shorter time period. It lasts 100,000 years.
It captures the earth as the temperature, and this blue line is another proxy for temperature as it’s sliding in to the most recent ice age. There are a lot of spikes that you see in the northern hemisphere that you don’t see so clearly in the southern hemisphere, but we won’t be concerned about those here. We’re looking at common trends across the earth. Now, we unpack what has happened to us as a species in more detail. The first successful migration of fully modern humans out of Africa was about 85,000 years ago.
You see that there was a dip in temperature which means that sea levels dropped. It was easy for humans to migrate out of Africa, and they did. They went around the Arabian Peninsula, moved on through around the Indian subcontinent through the Indonesian archipelago. The earth was getting even colder through that time. Sea level is dropping even further.
We were connected to New Guinea, Tasmania was connected to the Mainland, and so on. The first wave of fully modern humans ended up here. In fact, it branched at the very end between New Guinea and Australia. Indigenous Australians are the endpoint of the first wave of fully modern humans out of Africa. They left groups of people all the way long, and indeed some continent, and so on.
Some of those later on then, set migrations up from South Asia into Europe. Now, those of us of European descent, and I’m primarily of European descent, I can trace my mitochondrial DNA. In fact I can trace mine back to that second red here or about 33,000 years ago, but I come from South Asia originally. Basically, all of us who are Europeans come originally from South Asia and originally from Africa. Again, look at this ice core record about 10,000 years ago, the earth became very much steadier in climate.
It was warmer, carbon dioxide was much higher, plants were growing better, sea levels are rising too starting to isolate us again. As the sea levels rose by 120 meters between the bottom of the ice age and that period then. The geologists actually have a name for that 10,000-year period with a blue line. It is zero which is a simply a reference temperature, and it stays there pretty steadily. That’s called the Holocene. That’s still the official epoch that the earth is in.
We’re suggesting now that we’re moving out of that epoch, out of the Holocene and into the Anthropocene. What has happened during that 10,000-year period of unusual warmth, and reasonably steady climate, although rainfall has gone up and down through that period? First of all, about 10,000 years ago, we saw the beginning of agriculture. Very interestingly, it appeared pretty much simultaneously at four different places on the planet. Most people associate it with the Middle East, with present day Syria, Mesopotamia, and so on.