Rain forests — lungs of the Earth?

By Frederic Friedel

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.

But my simple question was: if the Amazon rainforest is extracting carbon 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 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 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 350 billion tons, 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 the total amount has not been increasing in millions of years. True also, that if we returned all the carbon stored by plants to the atmosphere that would have catastrophic consequences. Actually that 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 were stored in permanently sealed caverns, as 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.

As I have said before: 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 of the 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, and 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 Heinz and 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.

Addendum: Today (October 8, 2018) the Washington Post published a report that backs up much of what I said. One passage quotes Erik Solheim, the executive director of the U.N. Environment Program, saying that we need to either stop emissions entirely by 2050 or find some way to remove as much carbon dioxide from the air as humans put there. He continues:

The latter would be used as part of a currently nonexistent program to get power from trees or plants and then bury the resulting carbon dioxide emissions in the ground, leading to a net subtraction of the gas from the air — bioenergy with carbon capture and storage, or BECCS.

Or bury the carbon-laden new vegetation. Actually what we need is a way to store the carbon dioxide generated by bioenergy not as a gas but as a stable compound, just like nature has done for billions of years (e.g. by the massive production of carbonate rocks and limestone). Come on, scientists, you can do as well as microorganisms (corals, foraminifera). Maybe we can build beautiful white cliffs in the process?!

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.