Are the “lungs of the earth” burning?

We urgently need to save the Amazon rainforest, but not for the reason usually given

Before I embark on today’s subject let me make perfectly clear, as I have done before: I am passionately in favour of saving the Amazon rainforest. In fact I have advocated that we, Europeans and Americans, should buy Amazonia, all two and a half million square miles of it, and preserve it for our progeny. It comprises more than half of the planet’s remaining rainforests, and is the largest, most bio-diverse area of the world. A great and precious treasure.

Having said that, I am most gratified to see that people all over the world, prominent people, are joining in the plea to save the Amazon rainforest. This took a special place in the news during the past month, when we were told that an unprecedented number of fires were burning in the rainforest. It was cause for great alarm. And the prime reason for alarm? Let me quote French President Emmanuel Macron, who on August 22, 2019, tweeted: “The Amazon rain forest — the lungs which produces 20% of our planet’s oxygen — is on fire.”

Others chimed in — celebrities like Madonna, Leonardo DiCaprio, Cristiano Ronaldo took to social media to say essentially the same thing: “The Amazon Rainforest produces more than 20% of the world’s oxygen and its been burning for the past 3 weeks” (Ronaldo on Twitter, DiCaprio even donated five million dollars to the cause). Another meme that was repeated by an endless stream of experts in the news media was: “The Amazon provides one of every five breaths you take.”

Now I spent some time considering: is this a good thing? It helps achieve the end I wish for: preserving the rainforest in South America. One could do the same by convincing people that Amazonia is somehow preventing asteroid impacts, or earthquakes, or devastating volcanic eruptions. But: is it expedient to give false reasons to support an important goal? Unfortunately not. At some stage the fallacy will be uncovered and the entire enterprise will be discredited.

First let me correct one factoid that politicians, celebrities and journalists keep getting wrong: the number of fires we have been seeing in 2019, and the area that is affected is not “unprecedented in the history of the Amazon rainforests.” In fact it is fairly average, as you can see in this BBC report:

In the first eight months of this year the NISR counted around 87,000 fires, as compared to 49,000 in the same period in 2018. But Brazil experienced more fire activity in the 2000s — there were more than 142,000 fires in the first eight months of the year 2005. It is quite normal in the dry season, with the fires starting naturally or, unfortunately, they are started by farmers and loggers clearing land for crops or cattle grazing.

The main fallacy in the news stories, however, is that Amazonia does not in fact produce 20% of our planet’s oxygen, in any sense of the word. It is not responsible for every fifth breath we take. I dealt with this in a in a previous Medium.com story, where I asked: do the rain forests actually produce oxygen or merely recycle it? It is one of the most-read articles I have published on my biographical and general interest blog. Also the most criticised. I will allow scientist to repeat my arguments in greater detail at the end of this piece.

Not one breath

I understand that it is difficult to accept my conclusions, which are not shared by the popular media. It was difficult to find any outspoken allies — until now.

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One Strange Rock, a science feature that premiered on National Geographic in 2018, is in my humble opinion one of the finest and most watchable television documentaries ever made. It tells us how life survives and thrives on planet Earth. One Strange Rock is hosted by actor Will Smith and features contributions by eight astronauts who have spent time (about 1000 days) on the International Space Station, viewing the Earth from above.

In the very first episode Amazonia and the “Lungs of the Earth” question are addressed, supporting exactly what I have been saying. You can watch a small part of this segment by clicking on the following link:

The above three-minute excerpt starts with astronaut Jeff Hoffman, who spent fifty days in Space, and Jerry Lininger (143 days) describing how you see, orbit by orbit, gigantic dust storms from the continental Africa crossing the Atlantic ocean and hitting the coast of South America. Lininger explains:

“As they grow the plants and the trees turn carbon dioxide into oxygen. One single tree can produce enough oxygen to support two people — and the Amazon rainforest is ten times the size of Texas, producing twenty times more oxygen then all the people on the surface of the Earth could consume. BUT: not one breath of it leaves the Amazon. There are so many animals in the Amazon basin that the life there uses all that oxygen up.”

Anchor Will Smith takes over: “For all these years I have been thinking the rainforest is ‘the lungs of the planet.’ Sure, it makes a lot of oxygen, but it uses it all.”

The episode goes on to explain who are really responsible for the oxygen in our atmosphere: “Diatoms, tiny marine organisms which smaller than the width of a hair.” I urge you to watch One Strange Rock, which is currently available in Netflix. It is extremely informative and visually stunning.

Anyway: if we are looking for the source of oxygen in the atmosphere we need to go to the oceans. That’s where most of atmospheric carbon dioxide is dissolved, and that’s where phytoplankton, microscopic organisms invisible to the naked eye are using photosynthesis to extract carbon from the CO2, and in the process releasing two oxygen molecules into the atmosphere. They, and not Amazonia, are providing the oxygen we breathe; they are responsible for the development of the oxygen-breathing creatures that inhabit the Earth.

Will Smith: “Take a breath. Now take another. Now think about this: one of those breaths was entirely provided by those little fellas under the sea.”

So what about Amazonia, does it provide nothing? In my previous article my reasoning was as follows: if it actually were the case that the Brazilian rainforest was constantly extracting CO2 — carbon dioxide — from the atmosphere, and releasing oxygen which we inhale (with every fifth breath), we need to ask a very simple question: where’s the carbon? In the plant mass people say. But those 150 billion tons of vegetation have been around, in essentially the same quantity, for hundreds of thousands of years. No additional biomass, which would store additional carbon is being generated every year. Search as you will there is no giant repository of carbon to be found in the rainforest.

In the case of phytoplankton we know exactly where the carbon that they extract from the (dissolved) CO2 goes: to the ocean floor. There we find a half-mile thick layer of the remnants of these microorganisms, carbon that has been stored for tens of millions of years, with more being added to it, layer by layer, each year. The oxygen they have released in the process is what keeps creatures like us alive — every second breath is supplied by them.

Of course it is true that returning all the carbon stored by plants in Amazonia to the atmosphere would have catastrophic consequences. Actually it is similar to what we are doing now, with oil and coal. These are gigantic carbon sinks created by geological processes over millions of years: plants and trees died but did not decompose — they were pushed under the surface of the earth into anaerobic layers, where trillions of tons of carbon have been stored in permanently sealed caverns, as oil and natural gas. Well “permently” until homo sapiens came along and started drilling it all out again, releasing the carbon back into the atmosphere, while consuming atmospheric oxygen in the process.

Science Background

Thankfully it is not just the popular media in shows like One Strange Rock that inform millions of people worldwide — I have been able to find a fair number of scientific papers and articles that correctly address the subject. Here are two you should read:

Yadvinder Malhi: Does the amazon provide 20% of our oxygen?
The phytoplankton in the oceans photosynthesise, generating around 240 Pg (petagram: one Pg is 1¹⁵ g, or a thousand million million grams, also often called a gigatonne, a thousand million tonnes) of oxygen per year. Total global photosynthesis (land and sea) produces about 570 Pg of oxygen per year. Therefore in terms of TOTAL global photosynthesis, photosynthesis in the Amazon contributes around 9%. This is small, but still substantial.

A bigger point that is often missed is that the Amazon consumes about as much oxygen as it produces. This is shown in the diagram. Plants produce oxygen through photosynthesis (green arrow). However, the the same plants consume the equivalent of over half the oxygen they produce in their own respiration (blue arrows). Plants metabolise as animals do, just at a slower rate, and at night when there is no photosynthesis forests are net absorbers of oxygen. The remaining 40% of the Amazon oxygen budget is consumed mainly by microbes breaking down the dead leaves and wood of the rainforest, a natural process called heterotrophic respiration (dark blue arrows). These process of plant and heterotrophic respiration are effectively the reverse of the photosynthesis equation above.

So, in all practical terms, the net contribution of the Amazon Ecosystem (not just the plants alone) to the world’s oxygen is effectively zero. A final point to make is that the atmosphere is awash with oxygen, at 20.95% or 209,500 ppm (parts per million). Carbon dioxide, by comparison, is around 405 ppm, over 500 times less than oxygen, and rising by around 2–3 ppm per year. Human activity (around 90% of which being fossil fuel combustion) has caused this oxygen concentration to drop by around 0.005% since 1990, a trivial amount. In parallel, the same activities have caused carbon dioxide concentrations to rise by by 37 ppm since 1990, or 10%. This is a much more substantial percentage because there is so little carbon dioxide in the atmosphere to begin with, so human activities that emit or absorb carbon dioxide can make a major difference. This is why we need to worry about the increase of carbon dioxide in the atmosphere (and its resulting impact on climate), and why we don’t need to worry about running out of oxygen.

National Geographic: Why the Amazon doesn’t really produce 20% of the world’s oxygen — “Of the many important reasons to worry about the thousands of fires raging in the world’s largest rainforest, oxygen supply is not one of them. Trees don’t just exhale oxygen — they also consume it in a process known as cellular respiration, where they convert the sugars they amass during the day into energy, using oxygen to power the process. So during the night when there’s no sun around for photosynthesis, they’re net absorbers of oxygen. … Trees inhale a little over half the oxygen they produce this way. The rest is probably used up by the countless microbes that live in the Amazon, which inhale oxygen to break down dead organic matter of the forest.”

My previous Medium.com article: Rain forests — lungs of the Earth?
Do they actually produce oxygen or merely recycle it?

Written by

Frederic Alois Friedel, born in 1945, science journalist, co-founder of ChessBase, studied Philosophy and Linguistics at the University of Hamburg and Oxford.

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