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Friday, January 11, 2008

The Earth's Lungs?

The following multiple choice question appeared on my eight year old daughter's homework:
Which of the following is the reason that tropical rain forests are called the Lungs of the Earth?
The answer was:
They breathe out more than 20% or the Earth's oxygen.
I had never heard that specific tidbit before and initially thought, "Oh, well, that's interesting." But then I thought about it a little more and quickly came to the conclusion that the answer was nonsensical. The first thing that struck me was the 20% figure. Twenty percent of what? Total oxygen in the atmosphere? That seems unlikely. Twenty percent of all oxygen consumed? Must be it, but that's not made clear by the answer.

But the "breathe" and "Earth's lung" concepts seem even more problematical to me. After the oxygen is breathed out, is it all breathed back in? If so, that's just another way of saying that twenty percent of the Earth's total metabolic processes occur in the tropical rain forests and that they are their own lungs, not lungs for the Earth.

The other choice is that the tropical rain forests breathe out and the oxygen is exported to the rest of the world. Indeed, that's what the answer to the question seems to imply. But where does this oxygen come from? I think the only plausible choice is that it's stripped from CO2. But if the rainforest is a net exporter or "O", then there's that pesky residual "C" left laying around in the forest. If the carbon isn't somehow also exported, it will start to pile up. I don't think much of the carbon is exported in any other form than CO2 (which requires "O" to produce). Therefore, if oxygen is exported, we would see a net increase, year after year, of carbon based compounds in the tropical rain forests.

I don't think that happens. Sure, when a tree grows it collects carbon. But when it dies, it rots and the carbon is converted back to CO2 by insects, fungi, micro-organisms, etc. The tree starts as nothing and ends as nothing. All of the tree, including it's leaves, seeds, etc., are ultimately consumed except for tiny fractions on average that may get buried. But I find it unlikely that those tiny fractions add up to anywhere near 20% of the earth's consumed oxygen.

I didn't (and still don't) know if my analysis was correct. So, I googled it. Many sites confirm the concept of the tropical forests being the earth's lungs. Here's one for example:
The Amazon Rainforest has been described as the "Lungs of our Planet" because it provides the essential environmental world service of continuously recycling carbon dioxide into oxygen. More than 20 percent of the world oxygen is produced in the Amazon Rainforest.
However, numerous others agree with my analysis. Wikipedia, for example, states:
Tropical rain forests are also often called the "Earth's lungs", however there is no scientific basis for such a claim as tropical rainforests are known to be essentially oxygen neutral, with little or no net oxygen production.
What do you think? Who's right? Is my child being fed bogus propaganda? Or scientific fact?


Howard said...

Silence comrade! You'll disrupt the brainwashing.

Harry Eagar said...

Total free oxygen has been unchanged for at least several hundred million years.

Unless total free carbon dioxide really is resulting in net increased biomass, in which case total free oxygen would also increase in the same proportion.

Total free oxygen was once much higher than now but found an equilibrium point. In that sense, biological activity can be thought of as a reverse lung, but lungs are a zero-sum activity (almost): O in and CO2 out, whereas the reverse lung is CO2 in, O out.

Whether 20% of respiration occurs in tropical forests or not, I don't know.

Humans are oxygen sinks. You could just as well say that killing off half of us would enhance the 'lung power' by eliminating a huge sink.

Anonymous said...

Years ago, when I was working for an environmental group challenging mega-project development in the North, we used to call the river systems the "bloodstream of the Arctic". The kids loved it.

But you get in there, Bret. Call the teacher and tell her you want to address the class and tell the kids all about that pesky residual "C". Let us know how you make out.

Bret said...

If I were going to do anything about it other than point out to my kids that statements like that aren't always what they seem, I would write to the publisher of the textbook. The teacher is just following the book. She's a fine teacher and I wouldn't want to burden her.

erp said...

"Is my child being fed bogus propaganda?"

Is you serious?

It gets far worse as the child progresses through the system. Brace yourself for it, or get her out ASAP.

Lungs breathe in oxygen and “breathe out” CO2, so the analogy is false and even if the percentage is correct, why* would an 8 year old need to know the precise percentage of oxygen "breathed out" by the tropical forests? (I’m impressed they’re even being taught percentages and decimals at eight).

All forests “breathe out” oxygen, not only those in the tropics. Even the geranium in the little pot on the front steps “breathes out” oxygen.

*Other for propaganda purposes, I mean.

Anonymous said...

Bret, I'm sure she is a wonderful teacher. Just like the favourite teacher who held my son up to ridicule and asked him in front of the class whether he believed the world was flat when he came to school with articles showing not all scientists buy into the party line on global warming.

They really don't like to be told inconvenient truths.

Harry Eagar said...

Yeah, after NCLB destroys the bad old public schools, all the kiddies can go to the kind of school I went to, where I learned about the concept of the one-way safe conduct.

Among other nonsense.

Bret said...


My wife suggested that I email or talk to the teacher. As your example shows, I think there is more downside (for my daughter) than upside (for anyone) by doing anything with the teacher here.


What's the concept of one-way safe conduct?

erp said...

Why not go back to the public schools I went to where leftwing politics weren't brought into every discussion and we learned stuff. Even the Catholic grammar school only brought up religion in religion class, not arithmetic and grammar. American history may have been a little heavy with the exploits of Jesuits, but otherwise was pretty even handed -- and they didn't make things up.

Bret - you're right that talking to the teacher will effect your daughter negatively as will bringing articles or otherwise showing her that the propaganda she's teaching is factually wrong. Text book publishers are on the same page.

I used to be on the text book selection committee in our town. About 20 years, I resigned due to a disagreement with the content of the books submitted by the publishers, all of them. I haven’t seen a textbook since then, but I imagine they only got worse, not better.

One thing I don’t understand is why Orrin Judd is such a champion of public schools. Is he just being ornery to stir things up? He can't be serious.

Harry Eagar said...

He isn't a champion of public schools He just sends his kids to one because he won't put his money where his mouth is.

My father, whose finances were much worse than Judd's, made great sacrifices to send us to Catholic schools.

Draw your own conclusions.

The one-way safe conduct was offered to Jan Hus to go to Rome, where he was burned at the stake.

Believe it or not, 500 years later my Catholic school teachers were defending that as reasonable.

It isn't true that religion only came into religion class, at least not at any of the Catholic schools I went to. It came into all of them.

And it isn't true that the teachers didn't just make things up.

I was taught, for example, that India and China were Catholic countries.

erp said...

Harry, I'm sorry you had such a bad experience, but it was far different from mine. When I got to the public high school, there was no overt propaganda although I did think the leftist point of view was more popular, we got a great education.

There are private schools without religious association.

Hey Skipper said...

Phytoplankton (from Greek phyton, or plant), autotrophic prokaryotic or eukaryotic algae that live near the water surface where there is sufficient light to support photosynthesis.

75% of the Earth's surface is covered by water.

One heck of a lot less than that is covered by the Amazon.

I'm calling shenanigans.