[strainer]

The blogged claim that Amazon "consumes about as much oxygen as it produces" is not sourced and the piece seems to fly in the face of professional work on the subject. eg: "The global oxygen budget and its future projection" [1]

> Fig. 4 summarizes the annual averaged global O2 budget from year 1990 to 2005, with the mass of O2 in gigatonnes (Gt) listed in each sink and for each process mentioned above (see Section 2.5). The inputs of O2 to the atmosphere by land and outgassing from oceans are quantified as 16.01 and 1.74 Gt/a, respectively. ....

[1] https://www.sciencedirect.com/science/article/pii/S209592731...

[BurningFrog]

Let's demystify how plants "produce oxygen".

They do it by splitting CO₂ molecules. The oxygen part (O₂) goes into the air, and the carbon (C) part becomes the plant.

So for the Amazon to continually produce surplus oxygen to the atmosphere, it must also continually produce an ever expanding amount of plant material ("wood") that would form an ever growing pile there.

This is not happening. Because forests don't produce surplus oxygen. Our atmosphere doesn't work that way.

https://en.wikipedia.org/wiki/Photosynthesis

[EB66]

> This is not happening. Because forests don't produce surplus oxygen. Our atmosphere doesn't work that way.

This is just plain wrong. The blogger is completely wrong on this point as well.

In normal atmosphere conditions, photosynthesis does result in net oxygen gain. Plants do require oxygen for respiration, but they require far less oxygen than what they produce during photosynthesis. Furthermore, at night when there's no light, plants do absorb oxygen and give off carbon dioxide in order to continue respiration -- but the amount of oxygen given off during the day is typically ten times greater than the quantity of oxygen consumed at night.

> This reminds me, as we should all be reminded on a regular basis, the bulk of the things you read in the popular press are at best skimming the surface and at worst outright misleading due to grabbing onto one obscuring factoid instead of the most important pieces of information.

Similarly, we should all be reminded that when skimming blogs and comments you're likely to come across misleading and inaccurate content. Scientifically inaccurate content like this gets posted on HN and blindly upvoted all the time.

[shkkmo]

> The blogger is completely wrong on this point as well.

I think you may not have read the article closely enough:

>> 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 ... my own team's research suggests this is more like 60%

>> 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

> Similarly, we should all be reminded that when skimming blogs and comments you're likely to come across misleading and inaccurate content

The "blogger" who wrote this article is "Professor of Ecosystem Science, University of Oxford" and "Founding Director, Oxford Centre for Tropical Forests" and probably knows more about this than you or I. This is not a peer reviewed paper, but it is probably more accurate than science journalism by a non-ecologist on this topic.

[strainer]

> my own team's research suggests this is more like 60%

My point was he hasn't cited that research - if it is concluded ? published? reviewed?

He seems to be just having a technical rant about a contextual phrase while giving the impression that forests in general, or at least the amazon or equatorial forests do not help maintain the atmospheres oxygen content. That would certainly be a maveric proposition at this stage in Earth sciences.

[shkkmo]

> My point was he hasn't cited that research - if it is concluded ? published? reviewed?

I am far more willing to take the word of an established and respected expert who understand the subject mater than a random internet person with a poorly contextualized citation. You can find the author's published papers on this and related subjects quite easily at the top of the article.

> He seems to be just having a technical rant about a contextual phrase while giving the impression that forests in general, or at least the amazon or equatorial forests do not help maintain the atmospheres oxygen content. That would certainly be a maverick proposition at this stage in Earth sciences.

He is a scientist clarifying a technical subject that has been being misconstrued. There has already been plenty of damage done by people throwing around fake facts and pictures.

[strainer]

The problem is I feel that he has confused understanding of the subject here rather than clarifying it, which is an easy thing for anybody to do in a conversational article.

Here is a recent work[1] which substantiates matters that Amazons practical involvement in the planets atmospheric oxygen/carbon levels is really not as the professor felt like putting it as "effectively zero".

> Abstract: The response of the Earth’s land surface to increasing levels of atmospheric CO2 and a changing climate provide important feedbacks on future greenhouse warming6,7. One of the largest ecosystem carbon pools on Earth is the Amazon forest, storing around 150–200 Pg C in living biomass and soils8. Earlier studies based on forest inventories in the Amazon Basin showed the tropical forest here to be acting as a strong carbon sink with an estimated annual uptake of 0.42–0.65 Pg C yr−1 for 1990–2007, around 25% of the residual terrestrial carbon sink3,4. There is, however, substantial uncertainty as to how the Amazon forest will respond to future climatic and atmospheric composition changes. .... Here we analyse the longest and largest spatially distributed time series of forest dynamics for tropical South America. .... Our data show that mature forests continued to act as a biomass sink from 1983 to 2011.5, but also reveal a long-term decline in the net rate of biomass increase throughout the census period. The decline in net biomass change is due to a strong long-term increase in mortality rates, and occurred despite a long-term increase in productivity. While mortality increased throughout the period, productivity increases have recently stalled showing no significant trend since 2000. ....

[1]https://www.nature.com/articles/nature14283

Published in Nature: 18 March 2015 : "Long-term decline of the Amazon carbon sink"

[EB66]

> I think you may not have read the article closely enough

I did read the article closely :)

>> 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 ... my own team's research suggests this is more like 60%

>> 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

The author is stating that the Amazon rainforest is in perfect equilibrium without citing any studies or evidence. There are plenty of studies that indicate otherwise, such as this 30 year survey involving 100 researchers: https://www.nature.com/articles/nature14283

> While this analysis confirms that Amazon forests have acted as a long-term net biomass sink, we find a long-term decreasing trend of carbon accumulation.

But even if we accept the author's argument that today the Amazon is in perfect equilibrium -- I think it was misleading of the author not to clarify that in order for any forest to grow, it must be a net carbon sink and net oxygen producer up to that point in the forest's lifetime.

Now the comment that I originally replied to said something different. That comment argued that forests cannot be net producers of oxygen because there aren't "ever growing [piles of wood]" and then he provided the Wikipedia article for photosynthesis as evidence supporting that. That's wrong as I explained above.

You can have forests that are net carbon sinks and net producers of oxygen and you don't need "ever growing [piles of wood]" in order for that to happen.

[shkkmo]

> The author is arguing that the Amazon rainforest is in perfect equilibrium without citing any studies or evidence

The author argued no such thing, You are making up claims adn attributing them to the author, so perhaps an even closer reading of the blog post would be beneficial.

>> 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. The same is pretty much true of any ecosystem on Earth, at least on the timescales that are relevant to humans (less than millions of years).

The paper you cited is talking about carbon dioxide, not oxygen. The net effect on global O2 levels of carbon sequestration is minimal and not significant on human time scales. That same carbon sequestration has a significant impact on global CO2 because there is much less CO2 in the atmosphere.

[EB66]

> The author argued no such thing, You are making up claims adn attributing them to the author, so perhaps an even closer reading of the blog post would be beneficial.

Please go read the article again. That's exactly what he's saying. He is saying that Amazon rainforest O2 production and consumption are in equilibrium.

> The paper you cited is talking about carbon dioxide, not oxygen. The net effect on global O2 levels of carbon sequestration is minimal and not significant on human time scales. That same carbon sequestration has a significant impact on global CO2 because there is much less CO2 in the atmosphere.

For heaven's sake, please read the study. If you'd rather not read the study, then just Google until you find a satisfactory source that explains that net O2 production and net CO2 sequestration strongly correlate with one another.

[shkkmo]

> The author is stating that the Amazon rainforest is in perfect equilibrium without citing any studies or evidence. There are plenty of studies that indicate otherwise, such as this 30 year survey involving 100 researchers: https://www.nature.com/articles/nature14283

Y. Malhi, one of the authors of that paper, is also the author of this blog post. That makes sense since he a preeminent rainforest ecologist who publishes lots of papers on the carbon cycle.

[EB66]

Yes, you also pointed out this fact up above in the comment chain as well. And as @strainer pointed out, it leaves us with more questions than answers. Specifically: how could he have participated in the study but publish a blog post that contradicts the primary conclusions of the study?

[BurningFrog]

A single plant does produce oxygen while it's alive, and the carbon is bound in its growing body.

But that carbon is all released back as it decomposes after its death.

On a "whole forest/whole year" perspective, there is normally an equal mass of plants growing and being decomposed, and thus the net oxygen effect is zero.

[EB66]

> But that carbon is all released back as it decomposes after its death.

> On a "whole forest/whole year" perspective, there is normally an equal mass of plants growing and being decomposed, and thus the net oxygen effect is zero.

Sure, if you're talking about a timespan of one hour, one month, one year, etc then it's definitely possible for biological processes in a forest to expel carbon in the form of CO2 in equal volumes that were sequestered by plants. You could even have an overpopulation of some kind of insect or fungus cause a forest to temporarily become a net contributor of atmospheric carbon.

But over the lifetime over the forest, the net effect is obviously massive CO2 sequestration and massive O2 production. If the net carbon impact was zero over the lifetime of a forest, then forests would have no soil. But we know that not to be the case. Forests grow, they accumulate soil, etc.

Despite constant heavy rains and erosion, soil in the Amazon rainforest is often several meters deep and spans an area of over 2 million square miles. That's a lot of carbon sequestration!

[BurningFrog]

I agree that for a "startup" forest, there will be an accumulation of soil.

I assume it reaches an equilibrium after some time, and that the Amazon soil has remained the same "several meters" deep for many millions years.

But I'll admit I don't know that, and you may have a valid point. If real, this effect has to be quite small though.

[EB66]

> I assume it reaches an equilibrium after some time

Yep definitely and in part because CO2 only makes up ~0.04% of our atmosphere. Photosynthesis processes slow when CO2 levels fall and increase when CO2 levels rise. But as well as know atmospheric CO2 levels are rapidly on the rise and is outstripping the ability of large forests to sequester it.

[nearbuy]

Then where is the carbon going?

[EB66]

We're talking about oxygen production. Not carbon sequestration.

Regarding sequestration: the carbon goes into the trunk, branches, roots and leaves of the tree. Leaves fall off the tree, rot and become soil. The tree eventually dies, rots and becomes soil.

Some carbon will be given off by various decomposition processes, but the overall net effect is by far a carbon sink.

[nearbuy]

> We're talking about oxygen production. Not carbon sequestration.

BurningFrog said the carbon from CO2 goes into plants. Since plant matter isn't accumulating, carbon can't be accumulating, and therefore oxygen can't either. You replied, "This is just plain wrong".

So you're saying the part that is sequestered goes into the soil. That means some significant fraction of the 20 billion tonnes of carbon the Amazon photosynthesizes each year is turning in to soil. You're claiming the amount of soil increases by this amount each year, correct?

[EB66]

> That means some significant fraction of the 20 billion tonnes of carbon the Amazon photosynthesizes each year is turning in to soil.

Correct. That fraction is obviously reduced when the forest is burned.

[atoav]

Into the plant? Btw. you can easily test this yourself in a closed glas sphere.

[PeterisP]

Exactly, it goes into the plant, and is then released as the plant decomposes - so in a stable rainforest, where the total plant mass isn't increasing, the new plants growing (creating O2 and absorbing CO2) is fully balanced by old plants decomposing or burning (absorbing O2 and creating CO2); so there's no net creation of O2.

[varjag]

That would be true only if you always burn 100% of biomass, which doesn't happen. Carbon gets sequestered into soil, and partly consumed by insects and animals up the food chain.

All carbon in your body was once sequestered by plants.

[nearbuy]

I meant overall in the long term, in response to EB66 saying BurningFrog is wrong.

The plants can't be net collecting carbon each year unless the Amazon contains more and more plant matter each year.

[strainer]

Into the amazon river and out to sea basically. Rain will wash a lot of matter that way.

[strainer]

If forests did not then some other body of plant mass would have to - erosion and weathering of rocks takes a lot of oxygen out of the atmosphere, and this needs replaced by biology by photosynthesis. In the long term this is the reason the Earth needs to "breathe", and plants are how it has done so. Plants die and are eaten by ranging animals, dispersing their material, creating soils and eventually sediments. This is a long cycle through which carbon is returned to ground, sometimes to metamorphic rock.

It takes place at a lower intensity than our burning of fossil material and forests in recent history. Regrowing forest, usefully captures carbon and releases oxygen more rapidly than mature forest, but of course not rapidly enough to make up for burning them down.

[mirimir]

The paper that you cite is talking about small changes.

> Under the Representative Concentration Pathways (RCPs) RCP8.5 scenario, approximately 100Gt (gigatonnes) of O2 would be removed from the atmosphere per year until 2100, and the O2 concentration will decrease from its current level of 20.946% to 20.825%.

    2018  209460 ppm
    2100  208250 ppm

That's 15 ppm per year.

From Stolper et al. (2016) A Pleistocene ice core record of atmospheric O2 concentrations:[0]

> We present a record of Po2 reconstructed using O2/N2 ratios from ancient air trapped in ice. This record indicates that Po2 declined by 7 per mil (0.7%) over the past 800,000 years, requiring that O2 sinks were ~2% larger than sources.

That's 7000 ppm decrease over 800000 years, or 0.009 ppm per year. And so yes, atmospheric oxygen concentration is dropping lots faster now. But TFA's point that it's slow, and regulated by long-term processes, is still valid.

0) https://science.sciencemag.org/content/353/6306/1427

[strainer]

So that's where he is getting the context for his rant >>

"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."

Practically, the reason why we have oxygen in the atmosphere is plant photosynthesis over long terms. We can quibble over the net annual product of every forest and ecosystem as he has - but over geological timeframes, the plant life they contain is the reason we have any oxygen to breath. And if the amazon currently amounts to about 20% of the plant life on earth now, its not wrong to teach that it is doing 20% of the oxygen maintaining.

The fact that long term maintenance is obscured by shorter term dynamics including our modern industrial activity, does not make a lie of the understanding and respect that forests are lungs of the planet.

[eveningcoffee]

I am lately thinking that we are assigning too less value to this fact. We all need oxygen and we should have enough forests to produce it and this means that we should globally subsidize forest keeping. It is not a single country problem. It is a global problem.

[nearbuy]

1. The article explained this isn't true. Carbon dioxide is a problem. Oxygen depletion is not. Burning enough forests to decrease atmospheric oxygen by just 1% would increase CO2 by 5000%. We'd be dead long before we ran out of oxygen.

2. I'm not sure what you have in mind for "short term" vs "long term", but oxygen levels only change significantly over hundreds of millions of years.

3. Just like a stable sized forest doesn't produce any significant net oxygen, humans don't overall use up oxygen from breathing. The plants you eat (or if you're eating meat, the plants your food ate) released oxygen into the air when forming the carbohydrates and fats you eat. Your body then recombines these with an equal amount of oxygen to produce energy.

[eveningcoffee]

Of course excess CO2 is greater problem than lack of oxygen but these things are in 1 to 1 correlation - you need oxygen to burn carbon. The more you burn carbon the more oxygen you join from the environment. To get the same oxygen back you need to breakup all the carbon you burnt.

If you destroy the forest then you will reduce the capacity to remove the CO2 from the atmosphere and produce oxygen or do you disagree with this?

[nearbuy]

Then why mention oxygen? It's irrelevant. It's like advocating that people should only shoot people with non-lead bullets so the victims don't get lead poisoning.

> If you destroy the forest then you will reduce the capacity to remove the CO2 from the atmosphere and produce oxygen or do you disagree with this?

The linked article explains this isn't true. The rainforest is in equilibrium. It doesn't remove CO2 overall. It's a carbon stockpile.

If you were to burn the forest, it would release the stockpiled carbon into the atmosphere as CO2.

[shkkmo]

> over geological timeframes, the plant life they contain is the reason we have any oxygen to breath

About 1/2 of the oxygen produced is produced by Phytoplankton, which are not plants (though they are similar).

> And if the amazon currently amounts to about 20% of the plant life on earth now

The amazon accounts 16% of the photosynthesis on land.

> its not wrong to teach that it is doing 20% of the oxygen maintaining.

It is wrong. If you want to provide a nice round, reasonably accurate number you should use 10%.

> does not make a lie of the understanding and respect that forests are lungs of the planet.

Forests are important and and a significant part of the respiration of them planet, but they are less important than our oceans. Our oceans are the true lungs of the planet (edit: and they are not in great shape, atmospheric oxygen may not be an issue, but oxygenation of the ocean is more variable).

[mirimir]

Sure. But long term, the Sahara may green, and "replace" the Amazon. At this point, I'd worry more about the oceans.

[strainer]

Burning the amazon down is something to worry about. Not afforesting widely and extracting timber from the amazon ecologically so it sequesters carbon and supplies materials replacing demand for carbon intense alternatives - is tragedy.

The advice that amazons contribution is "zero", hedged under this safety-net word "effectively" is false to the understanding of geophysics and natural history. I hope the professor will clarify his language after consideration.

[mirimir]

I'm not arguing that it's not something to worry about. It certainly is something to be worrying about. But so are the tropical forests of Southeast Asia, which are arguably even more threatened.

But we should be worried about it because of the impact on global biodiversity. Not because we'll be running out of oxygen. Having ~20% oxygen in the atmosphere reflects a long-term equilibrium of biologic and non-biologic processes.

If advocates focus on the oxygen issue, adversaries can easily point to negligible changes, and argue that there's nothing to worry about.

And, as I said, to the extent that oxygen is an issue, we ought to worry even more about the oceans. They are by far the major oxygen source, and arguably more vulnerable to catastrophic collapse.

[shkkmo]

> the piece seems to fly in the face of professional work on the subject.

The blogger does professional work on the subject. The article makes it pretty clear that the net positive production of oxygen the the Amazon is so close to zero that it is only relevant on the time scale of millions of years.

[james_s_tayler]

One Strange Rock documentary on Netflix makes the same claim.