Arquivo de etiquetas: holoceno

The antropocene V – Holoceno e Antropoceno

Where we introduced the big picture, the science behind the evidence showing that we can welcome humanity to the Anthropocene, the Quadruple Squeeze on planet Earth, and the Great Acceleration of the human enterprise.

This coming week, we’ll now explor211e the Anthropocene in much more depth, digging ourselves into the different perspectives and visions on the Anthropocene. Professor Garry Peterson, one of our senior head researchers in regime shifts at the Stockholm Resilience Centre will be joining us this week. And please don’t miss our first hangout at the end of this module.

To understand the human predicament in the globalized phase of environmental change, in a situation where we recognize increasingly that the Earth system self-regulates its stability and that it could push itself away from its current stable state if we trigger the planetary system too far. We must explore something profoundly important in order to help us in the pursuit of global sustainable development, namely to identify what is the desired state of planet Earth?212

We often illustrate it in the following way, namely showing in different cups the stable states that an ecosystem, or in this case the entire planetary system, can reside in. So one of the largest and most important questions for science today is what is the desired state of planet Earth to support the modern world as we know it? And what is really exciting is that science increasingly shows that we have an answer to this question.

And the answer originates, not surprisingly, from paleoclimatic data on ice cores. Now you’ve probably seen this set of data, the fantastic evidence going all the way back almost 1 million years, here at the ice core data going back 800,000 years, showing temperature variability over this period, and the twisting and churning of the Earth system in and out of two stable states; namely, the deep glacial states, the cold, lower points in these graphs that often have a duration of roughly 120-150,000 years, separated by relatively short periods of interglacial warm periods where we have essentially an ice-free state of the planet with ice in the caps.213

Now what is really interesting with this graph is to look particularly at the last two interglacial periods. You see the label Eemian, and then you see the label Holocene. Holocene is the period that we are in right now, the period where we’ve been for the past 10,000 years. But the last time we had a warm interglacial is the Eemian, roughly 120,000 years back. Now this period is interesting because over several thousand years it was two degrees warmer than what we have today in the Holocene. And research shows quite clearly that during that period of 2 degrees Celsius warmer than what we have today in the world of the Holocene, sea levels were in the order of 4-6 meters higher than today.

And this is to me an enormously clear reminder that the Earth system actually has stayed over very long periods of time within very narrow bands of environmental boundaries or levels, and that even small changes can lead to very, very abrupt and large shifts in life conditions on Earth, in this case manifested at sea level rise.214

What you also observe from this curve is something quite extraordinary. On the Y axis you see that temperatures on average change with only +/-4 degrees Celsius, and that’s the difference between having two kilometers of ice above our heads, and the warm, lush environmental conditions that we are so used to in the world of today.

So this is one reminder of the extraordinarily important insight that the environmental conditions on Earth vary and that we have stable states. But let’s not go into trying to answer the question of what is our desired state.

Then we can go into exactly the same data, which is shown here, but only over the past 100,000 years. So this is the last 100,000 years on Earth, again on the Y axis showing variability of temperature, a good proxy of how it was to live on Earth. And what you’ll see now is that this was indeed over almost the entire period a very jumpy ride for humanity indeed.215

We were hunters and gatherers during this period. We were a few million people and we had a very rough time because predominantly because of these enormously rapid jumps between very cold and very warm periods.

It’s an interesting period because we were modern humans during the entire phase, so we had the same ability, both physically and intellectually, to develop civilization as we know it.216

Recent genetic paleoanthropological data shows in fact that the cold point that you might there at roughly 75,000 years back when we had hundreds of meters lower sea level than today and most of the fresh water in the world tied up as ice in the polar regions, we’re probably down to only 15,000 fertile adults on Earth. We were hidden in the Ethiopian highlands and we had a very rough time of survival. We were essentially extinct. And we go through this entire very tough period and enter then this final stable phase which is shown in a circle here which we have learned in school to call the Holocene.

The Holocene is an extraordinarily stable phase for human development. In fact temperatures vary with only +/-1 degrees Celsius. And even though the genetic diversity has been around for millions, often hundreds of millions of years, it is now that everything we know in terms of ecosystems, nature, the biosphere, settles in.

This is where the rainforest, the coral reef systems, the temperate forests, all the wetlands, settle in and establish themselves very permanently in the state that we know. It is now the rainy seasons become predictable. It is now in the northern temperate zone we know that we have almost every year a hundred days of temperature, which allows us to grow food. It is now in the tropical regions we have a hundred days of secure rainfall, allowing ourselves to be able to produce food. And not surprisingly we barely enter the Holocene and what do we do?218

We embark on the most important invention of all time; we invent agriculture. And the exciting thing is that we invent agriculture right at the start of the Holocene in at least four different places simultaneously on Earth. And because we didn’t have SMS or e-mail or chat rooms it’s absolutely proven that this occurred entirely independent of each other, and because of the stable environmental conditions on Earth.

We go into the civilizational development starting off with agriculture, the Mesopotamian empires, the Egyptian empires, the Maya, the Chinese, the Latin American civilizations develop all the way to the great acceleration in the mid-1950s. We’re three billion people and then off we go in the Great Acceleration. We’re 7 billion people today, committed to 9 billion people.

And the scientific conclusion of this single graph is as simple as it is dramatic, that the Holocene is the only stable state of the Earth that we know can support the modern world as we know it.

We can live outside of the Holocene, the planet isn’t bothered, but we would probably not have any chance to support the modern world as we know it, soon with nine billion co-citizens.219

Now this simplifies life tremendously for humanity because we know the Holocene very well. We can define very well the environmental conditions that we need to fulfill in order to remain stable in the Holocene. We understand the carbon cycle, the nitrogen cycle, the phosphorus cycle, the big ecosystems, and this helps us tremendously in defining global sustainability.

Now the proof that we have had major problems during this period are shown in this graph showing the very large exodus that we were triggered or forced to embark on during periods of often very, very cold, dry, and food security-wise challenging situations for humanity. We also know during this period from data from Greenland that the jumps in temperature could be 10-15 degrees Celsius over just periods of decades.

In fact we have 25 such abrupt shifts over just the past 100,000 years, as evidence that it was a very, very difficult ride for humanity during this cold period before entering the Anthropocene.

So overall we need to recognize that the biomes and ecosystems in the world sustain and support the Holocene state of the world. That systems such as rainforests that regulate the carbon sinks in large parts of the rainforest systems, and the rainfall systems regionally; that we have coral reef systems that also regulate the resilience in the ocean, and the ability to circulate heat, and the ability to take up carbon dioxide; the large permafrost regions holding vast amounts of methane; the temperate forest regions that provide a canopy that reflects back heat back into space through its darker colour, but also massive carbon sinks; the systems on the savannahs which in turn regulate large parts of heat fluxes, rainfall trajectories, and also carbon sinks; are all systems that together form part of regulating the stable state of the Holocene.130a

And the conclusion is that we understand the Holocene, we need to preserve the Holocene, and the Holocene is the state that we know can support human development in the future.