Rain forests — lungs of the Earth?

Do they actually produce oxygen or merely recycle it?

Some years ago cousin Heinz came to visit. He was a forest scientist who subsequently advanced to become a professor with a University department all of his own. He is a very intense, athletic person, and I got into an argument with him. This is how it evolved:

At an evening dinner Heinz was expounding on the rain forests, which he called the “lungs of the earth.” In Brazil, the largest of the lot, they needed to be protected, vitally so in an age when climate change and carbon dioxide accumulation in the atmosphere is threatening our future. He quoted the acreage of rain forest that was lost to logging each year, and got a round of approving nods when he said this had to be stopped at any cost, if we were not all to suffocate. Or something to that effect.

Now I am passionately in favour of saving the rain forests; in fact I have advocated that we, the Europeans and Americans, should buy Amazonia from Brazil and surrounding countries, 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 and most bio-diverse area of the world. The Amazon basin has 400 billion individual trees of 16,000 individual species. And don’t get me started on the animal world it harbours, or the weather effects it has.

Also: after a couple of years of scepticism, I have become a firm believer in the dangers of global warming, brought about by human intervention. I turned because some of my smartest friends told me it was really happening — and because G.W. Bush (and now Donald Trump) said it wasn’t.

More recently I listened to the Sam Harris podcast with Joseph Romm: What You Need to Know About Climate Change. I challenge you to do the same without conclusively understanding that climate change is real and a result of human activity.

So I am not a climate denier with a hidden agenda. But I did have a practical question for Heinz: lungs of the earth? Are you implying that the Amazon rain forests are extracting carbon from the atmosphere in vast quantities and thus keeping us alive? Of course he was implying exactly that, and Heinz had concrete numbers to support his narrative: rainforests contain close to 50% of the carbon in the terrestrial biomass, with Amazonia clearly in the lead. He gave us the total mass of carbon contained in the soil and in the vegetation itself, which he expressed in hundreds of billions of tons. Deforestation was destroying this carbon repository in a way that threatened us globally, he said.

Image for post
Image for post
Image from CarbonBrief, which seems to agree with Heinz and writes: “The world’s forests provide a huge carbon sink, absorbing around a third of manmade carbon emissions, and helping to moderate global temperature rise… As part of the Earth’s natural carbon cycle, vast amounts of carbon dioxide are taken out of the atmosphere and absorbed by the land each year. Tropical rainforests … are responsible for much of that exchange.

But my simple question was: if the Amazon rainforest is extracting carbon dioxide from the air, gigatons of it, where is all this carbon being stored? In the trees, the wood, the biomass, of course, Heinz told me — and some of it in the soil. So over millions of years this grows to many billions of gigatons, I asked? And we find it in mountains of carbon, in some form or the other? Limestone, coal? Peatland, carbon-rich topsoil, hundreds of meters thick? Or are gigatons of carbon being washed into the oceans by the mighty rivers? These were innocent questions — I was really eager to understand how it all worked. But the professor of forestry became disconcerted. He did some real-time research — he sat in a corner for half an hour and thought. Then he said he would come back to me and explain everything on his next visit.

That did not bring the solution. Heinz had worked out that the Amazon basin currently stored something like 150 billion tons of carbon, with around two billion tons being absorbed from atmospheric CO2 each year (I am not sure about his exact figures — I did not jot them down at the time). So in a hundred years it would be 200 billion tons of carbon capture, I asked? And why was only 150 billion tons stored in the 50 million years this tropical rainforest has existed? Heinz was getting nervous: because some of the “sequestered carbon” stored by the plants and soil is returned to the atmosphere when trees “respire”. And when trees and foliage die they fall to the ground where they are decomposed by bacteria and fungi, a process that stores some of the carbon in the soil but returns most of it back into the atmosphere. Very little, if any, is added to the base of around 150 billion tons.

So how are tropical rain forests the lungs of the earth, if they do not, as generally implied, substantially change the total carbon balance of the planet, on a long-term basis? It is true that huge quantities of carbon have been accumulated by trees and plants, but that the total amount has not been increasing in millions of years. It is clear that if we returned all the carbon stored by plants to the atmosphere it would have catastrophic consequences. Actually that would be 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 were stored in permanently sealed caverns, as coal, oil and natural gas. Until homo sapiens came along and started drilling it all out again, releasing the carbon back into the atmosphere.

Are the hundred billion tons of carbon stored by the rain forests being basically recycled and renewed, while doing little for the overall carbon balance of the earth? This was my genuine question to Heinz, who was visibly distressed. I could not resist turning the screw a little further: “It seems to me that if we really wanted to extract substantial amounts of carbon from the atmosphere, the best strategy would be to chop down all the rainforests and bury the wood and foliage. New trees would grow and capture hundreds of billions of tons of new carbon, from the atmosphere?!”

Addendum: A friendly young ecology student, Emma, drew my attention to the fact that “burying” the wood would not achieve much, if anything. “Bacteria and fungi are present everywhere, and unless you enclosed all of that organic matter in an airtight container, nature would take its course and break it down.” You are right, Emma, but I meant exactly that by “bury” — not store it in the soil but in anaerobic caverns, where it could turn into oil and coal and stay permanently stored. The earth has been doing this for hundreds of millions of years.

As I have said before and would like to stress again: I am passionately in favour of preserving Amazonia and the rain forest. As son of a German herpetologist I spent part of my childhood in a semi-rainforest jungle, and treasure the memories from that time. Destroying rain forests for timber and agriculture is in my opinion a crime that has to be stopped. It has to be done, in my opinion, to preserve the jewels of the earth’s surface, but not, as Heinz believed, because rainforests continually extract vast amounts of carbon from the atmosphere. Because apparently they don’t. They are not in this sense the “lungs of the earth,” as countless articles on rain forests put it. They do not reduce the total amount of CO2 in the atmosphere.

It is possible that I have not understood exactly how the carbon cycle works for the rain forests. If that is the case will somebody explain it to me, please. Heinz couldn’t do it — and he has stopped talking to me.

Also read my updated article: Are the “lungs of the earth” burning?

We urgently need to save the Amazon rainforest, but not for the reason usually given. And coming soon: an article on how we humans use half a billion km² of the earth’s continental surface to produce food and sustenance; and how in doing so we utilize just 0.009% of the energy reaching this area from the sun. Quite wasteful — solar panels are 2000 times more energy efficient.

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.

Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store