Humans on Earth: A Brief Ecological History
How we turned the ecological world completely upside down and threatens our very own survival.
Many a history of humans have been told, but today let me offer you an extremely brief yet crucial narrative of our species from an ecological perspective.
It is a living history, and hopefully will still be a living history for generations to come, depending on the choices you and I make today.
This is the story about remarkable ecological and geological processes unfolding over billions of years that gave us both a breathable atmosphere and a massive stock of fossil fuel.
This is the story of how stored energy has catapulted our civilization into multiplicity and prosperity, but at the time threatens our own survival.
It is a story worth telling in its full glory. Remarkably, it is also refreshingly simple and elegant to tell, requiring nothing more than the most basic understanding of biology and arithmetic.
Let’s start with the sciences. How did earth become habitable for humans?
Nowhere else in the solar system is there a planet whose atmosphere is loaded with free oxygen. How did free oxygen come to be?
If you guessed photosynthesis then you’re dead on. The earliest photosynthetic organism was the blue-green algae. Most people nowadays know trees as significant photo-synthesizers. Ecologists call these solar creatures primary producers.
Through photosynthesis, trees capture and store solar energy in their trunks, roots, and leaves, producing oxygen as a by-product. Meanwhile, respiration does just the reverse, taking in oxygen, releasing energy and produces carbon dioxide. And not just animals respire, but trees also respire at night.
All in all, if we count all the oxygen and carbon molecules that go through these natural cycles, they all cancel out. That is required by chemistry. Essentially all the photo-synthetic products are respired away eventually.
So that means trees can act as carbon sinks? Yes, as long as they are living.
How do we know? Because we can see trees grow with our naked eyes, duh! Tree trunks and roots are made of carbon and the fact that carbon accumulates means that the oxygen has to be found somewhere else.
In the atmosphere, right? Not so fast!
Oxygen, mind you, is one of the most active molecules. It binds with just about anything. Iron, for example, turns rusty when combined with free oxygen. Indeed, geologists found that there was a point in time where every piece of iron on the surface of the earth went rusty, an event known as the Great Oxidation Event.
For this much oxygen to exist in the atmosphere, there is some process that produces the same amount of carbon somewhere hidden in the earth. Guess what? Those are what we call “fossil fuel,” which is basically fossilized organic matter that escaped decomposition.
When trees die, decomposers such as worms and bacteria break down the tree trunks and roots and emit CO2. This is why an old-growth forest stores tons of carbon in huge living trees, and why deforestation is bad because it releases tons of carbon.
But when these tree trunks and other organic matters sank to the bottom of the ocean and hid underneath rocks they became fossil fuel. To put it simply, fossil fuel was formed by an ecological imbalance that played out over hundreds of millions of years by motions of the mountains and the oceans.
On the one hand, a vast amount of free oxygen built up in the atmosphere. On the other hand, a vast store of carbon-based fossil fuel lie underneath the earth’s surface. They are the residual imbalances caused by geology for an otherwise perfectly reversible transient process: the dance of photosynthesis and respiration.
And life was plentiful until the rise of humans.
You probably know already that the invention of fire is a significant event in the history of homo sapiens. Fire produces light and warmth, gives us superior protection, enables cooking and brought tool-making to a whole new level of sophistication. Think pottery, alchemy, etc.
But from an ecological perspective, the invention of fire has an even greater significance. It marked a huge shift. Before this, nature had relied exclusively on solar energy from plants’ photosynthesis, and humans were second-hand beneficiaries by breathing in oxygen and eating the plants and animals for energy. We stood at the top of the food chain, while the solar creatures a.k.a primary producers lie at the bottom. Through the burning of firewood, we found a shortcut in the food chain to get solar energy.
The invention of fire allowed humans to access a STORED energy source that was as abundant as tree trunks in the forest. Abundant stored energy has allowed us, humans, to stay warm late at night, to migrate to colder climate where no man had gone before.
And we went forth and prospered.
But that was elementary. That was just the beginning of our civilization. That was primitive.
Because the scale of energy released by burning tree trunks and firewood was unremarkable before the advent of fossil fuel. In short, the discovery of coal ushered in the Industrial Age and put the Great in Great Britain.
The discovery of oil and the rise of automobiles and air travel have propelled humans to every corner of the world. We live like gods, flying through the clouds and enjoying the warmth of summer even in the middle of a freezing winter in the coldest places on earth.
We were kings of the world, or so we thought.
But remember the ecological imbalance of oxygen and carbon? And remember the time scale of a geo-ecological process that took us to where we are today?
We are, essentially, burning the stored energy reserve that took hundreds of millions of years to accumulate, releasing carbon and reversing an ecological process that gives us breathing oxygen in the atmosphere. What could possibly go wrong?
We are the thieves of the earth’s ecological past and our children’s carbon future.
A quantitative perspective matters here to help understand the stupendous scale by which we are burning down the world.
Just how much carbon are we releasing for our fossil-fuel dependent activities? If we instead burn firewood or biofuel, how big of a forest would we burn to get an equivalent CO2 emission?
It is estimated that human activity released 37 billion tons of CO2 into the atmosphere in 2018 alone. In contrast, a coniferous forest fire can release 20 tons CO2 for each acre burnt.
This means annual human activity is burning an equivalent of about 2 billion acres of forest fires.
Of course, it depends on the type of forest fires, but we can estimate above the figure in a simple way like this: 1 acre ~ 100 pine trees ~ 50 tons mass (assuming 500kg/tree) ~ 10 tons carbon (trees contain water and the wood cellulose contain molecules like oxygen, hydrogen, so we assume 20% of the mass is Carbon) ~ 30 tons CO2 when burnt. This is called a back-of-the-envelop calculation based on deep understanding and gives a roughly correct answer.
So, mankind’s annual emission roughly equals burning a forest with an area equivalent to that of the U.S. or the whole of Europe.
That’s an entire continent. Burned to the ground. Every single year.
Let that sink in for a moment.
That is the scale of destruction that our “civilized” life depends on, business as usual. It sometimes can be smelled but it is mostly hidden from plain sight.
We haven’t even talked about climate change, a most urgent problem caused by the stupendous level of carbon emission afforded by our society.
It is simple to explain: carbon in the atmosphere traps heat from the sun and increases the earth’s temperature. This is known as the greenhouse effect.
Many have talked about the catastrophic consequences of climate change: from frequent flooding, more destructive hurricanes, vicious snow storms and lethal heat waves. I’m not going to repeat them all here. If you want to learn more, a viewing of Al Gore’s “An Inconvenient Truth” would be gently recommended. Or if you have a tolerance for Stephen-King-style horror then go right ahead to read David Wallace-Wells’s “The Uninhabitable Earth.”
Truth is often times stranger and scarier than fiction. The urgency of the problem, our failure to act, and the catastrophic effects all make for a combination that can disturb the calmest mind.
So how to we get all that CO2 out of the atmosphere to save the planet? Since trees do take in and sequester carbon, can we simply plant more trees?
Sure, but how many trees do we need to plant to compensate for each year of human’s emission? In other words, is it possible to carbon-offset our so-called modern lifestyle?
The answer is actually the same number as above! We need to plant 2 billion acres of trees for each year of society’s carbon emission.
There are differences, however. First, it takes decades to grow a tree to maturity (whereas in a forest fire all the trees’ carbons are released at once). Second, the soil organic matter underground a forest can store as much as 10 times the carbon trees store aboveground. A forest fire only releases the above ground carbons but not those underground. These two effects cancel out and we get the same answer.
That is, every 5 years, we need to grow a forest with an area equal to the size of the whole Asia (around 10 billion acres).
Needless to say, this method of carbon-offsetting is unsustainable. We would simply run out of land.
So what now?
Can we live in harmony with the earth, not at its odds? Can we pull off this massive decarbonization of society?
Mind you, our dependence on fossil fuel energy goes way beyond electricity and transportation and deep into our way of life.
Fossil fuel goes into the food we eat when farmers use nitrogen fertilizer to feed the soil and chemical pesticides to spray their crops. Fossil fuel goes into the synthetic fabrics most of our clothes are made of. It goes into the cheap plastic toys our kids quickly destroy. It goes into the bags and straws that are choking our ocean, poisoning marine life and making its way into our drinking water and very bloodstream.
Breaking away from this fossil fuel addiction is not going to be easy. With all due respect to Al Gore, cleaning up this mess is going to require far more than a laundry list of ten things to do such as switching to an LED light bulb or to buy offset for your flights. Those are necessary, but far from sufficient.
Because we would need to fundamentally re-imagine how we live our lives and conduct commerce with net zero carbon emission. Project Drawdown list 100 of the most effective such solutions. There are countless others.
So whatever skills you have or whatever industry you are in right now, you have a transformative role to play: be it deploying and developing new technology, educating the public, organizing and leading people, fighting in courts or protesting on the streets.
In a way, your impact might be larger than the impact of any pure scientific research at this point in time. Because the science of climate change is really settled, and it’s dead simple to explain.
What are you going to do?
 A Citizen’s Guide to Ecology. Lawrence B. Slobodkin
 Direct carbon emissions from Canadian forest fires, 1959–1999, B.D. Amiro et al.