Does the Amazon provide 20% of our oxygen? • Hacker News Board

Re: Does the Amazon provide 20% of our oxygen?

#191

Post by mirimir » Sun, Aug 25, 2019, 3:20 PM UTC

jefftk wrote: post #172

Merovius wrote: post #145

Earlier quoted context omitted.

> 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 FTR, this article is doing exactly that. Like, they a) divert your attention with the CO₂ O₂ conversion (which doesn't change relative num…

The article is making a much stronger claim: > the net contribution of the Amazon ECOSYSTEM (not just the plants alone) to the world's oxygen is effectively zero If this is correct, then the entire Amazon could vanish without having any effect on CO₂ levels.

That's actually pretty much true. At least, if it literally "vanished", without releasing biomass carbon back to the atmosphere.

In temperate ecosystems, there's net long-term storage of biomass and nutrients in soil. Mainly roots of dead plants. But also stuff that accumulates faster than it can decompose. Tundra and taiga are extreme examples.

But mature tropical ecosystems are pretty much in equilibrium, with ~zero net impact on the soil or atmosphere. Pretty much all mineral nutrients are locked up. And everything that dies gets recycled very quickly.

Re: Does the Amazon provide 20% of our oxygen?

#192

Post by dcolkitt » Sun, Aug 25, 2019, 3:53 PM UTC

chewbacha wrote: post #186

dcolkitt wrote: post #182

Earlier quoted context omitted.

Some back of the envelope math... One tree in a tropical rainforest sequesters 50 pounds of carbon. The Amazon contains 390 billion trees. Since industrialization humanity has cumulative released about a trillion tons of carbon. So if the entire Amazon burned down it would increase atmospheric carbon by less than 1%. This is just a rough estimate, and I'd encourage others to check my calculations. But intuitively thi…

I agree that burning fossil fuels release more CO2 into the atmosphere. I was not trying to imply that the rainforest will halt global warming, obviously it can’t because it’s been there the entire time. However, I do believe just multiplying trees by weight does not accurately describe what carbon sequestration is. Trees are not the only place carbon is sequestered in a forest. Soil sediment, animals, and other plan…

> However, I do believe just multiplying trees by weight does not accurately describe what carbon sequestration is.

That's a fair point. The IPCC gives an estimate of 109 tonnes per acre of tropical forest. Which is about an order of magnitude higher than my original estimate.

But even with those numbers, deforestation is basically a rounding error compared to fossil fuel emissions. The Bolsonaro admin has increased deforestation rates by 278%, or an annual rate increase of 4500 sq km. Using the IPCC numbers, that's 110 million tonnes of Carbon per year.

That's less than one week of America's carbon emissions. Less than one day of global carbon emissions. The point is that from a climate standpoint, current rates of deforestation are largely inconsequential compared to fossil fuel emissions. It's almost certainly more effective to spend political and economic capital on energy efficiency and renewables.

Re: Does the Amazon provide 20% of our oxygen?

#193

Post by BurningFrog » Sun, Aug 25, 2019, 4:20 PM UTC

EB66 wrote: post #127

BurningFrog wrote: post #123

Earlier quoted context omitted.

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 prod…

> 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 th…

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.

Re: Does the Amazon provide 20% of our oxygen?

#194

Post by BurningFrog » Sun, Aug 25, 2019, 4:21 PM UTC

bad_user wrote: post #187

BurningFrog wrote: post #126

Earlier quoted context omitted.

There is this idea that the ecological balance is very fragile and easily destroyed. This is true, in a way, but it doesn't mean nature will dies. It almost always just means that nature will find a new ecological balance.

If nature finds a new ecological balance that's incompatible with human life, does it matter?

This is more a Hollywood movie plot than something that really happens.

Re: Does the Amazon provide 20% of our oxygen?

#195

Post by EB66 » Sun, Aug 25, 2019, 4:49 PM UTC

nearbuy wrote: post #151

EB66 wrote: post #142

Earlier quoted context omitted.

> 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.

Then why is the soil layer in the Amazon only about a meter deep after millions of years of carbon sequestration? The rainforest photosynthesizes about 3 kg of carbon per square meter per year.

The soil is not only a meter deep. In most places it's several meters deep and it's that deep despite constant heavy rains and erosion.

The soil does not need to be millions of meters deep in order for the forest to be both a net carbon sink and net positive oxygen producer -- it can slowly acrue over time.

And even if biological respiration processes in the forest began to equal carbon sequestration processes -- the forest would still be a massive carbon sink over its lifetime given the massive quantites of plant matter and soil present.

Re: Does the Amazon provide 20% of our oxygen?

#196

Post by EB66 » Sun, Aug 25, 2019, 4:55 PM UTC

shkkmo wrote: post #170

EB66 wrote: post #164

Earlier quoted context omitted.

> 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 leve…

> He is saying that Amazon rainforest O2 production and consumption are in equilibrium. where? > net O2 production and net CO2 sequestration strongly correlate with one another. yes, but we have ~500 times more O2 than CO2 in the atmosphere so the effects on atmospheric composition are not anywhere close to equivalent. edit: Let me put it another way. We have so much oxygen that if we were to use any significant amou…

I think you need to look up the definition for "equilibrium" and then re-read the article once more...

Either way I'm done with this tangent.

Re: Does the Amazon provide 20% of our oxygen?

#197

Post by strainer » Sun, Aug 25, 2019, 5:04 PM UTC

shkkmo wrote: post #156

strainer wrote: post #146

Earlier quoted context omitted.

> 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 st…

> 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 technica…

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"

Re: Does the Amazon provide 20% of our oxygen?

#198

Post by strainer » Sun, Aug 25, 2019, 5:11 PM UTC

nearbuy wrote: post #128

EB66 wrote: post #127

Earlier quoted context omitted.

> 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 th…

Then where is the carbon going?

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

Re: Does the Amazon provide 20% of our oxygen?

#199

Post by hanche » Sun, Aug 25, 2019, 6:04 PM UTC

Armisael16 wrote: post #48

didbsivdf wrote: post #41

Earlier quoted context omitted.

“Not if it's turned into a ranch!” That’s not obvious to me. Most plants are C2 plants, but grass is a C4 so it captures sunlight more efficiently. Not to say burning the Amazon isn’t a terrible idea.

Plants pretty consistently are ~40-50% carbon by mass, so the amount of biomass on the ground is a fairly solid indicator of the amount of carbon sequestered. Unless the ranchers have a truly massive amount of hay at all times I don't see how a ranch can approach a forest.

Don’t forget the soil. Old prairie has immensely thick soil, with a high carbon content. Think deep plant roots. With the right management, ranchers could mimic the prairie ecosystem, restore and build soil, and sequester carbon into the soil. It’s not easy, but the most successful farmers have been astoundingly successful.

Not that any of this is a valid excuse for burning down the Amazon.

Re: Does the Amazon provide 20% of our oxygen?

#200

Post by cmrdporcupine » Sun, Aug 25, 2019, 6:25 PM UTC

DenisM wrote: post #190

cmrdporcupine wrote: post #179

Earlier quoted context omitted.

Temperate forests sequester carbon over millions of years by leaving a layer of carbon rich top soil beneath them through leaf and other litter fall. Soil can hold a _lot_ of carbon per square foot. Carbon that is partially lost to the atmosphere when it is plowed. But my understanding is that tropical forests tend to have fairly carbon poor soils on the forest floor.

The only way it could work is for the top soil to grow thicker by the year, reaching huge depths over tens of millions of years. As I recall my temperate forests, the topsoil is skin-deep, relatively speaking.

If you take a core sample from an established forest it's often got at least 5-6 feet of heavy dark carbon rich soil beneath. That's the case on my property anyways. I had some trees moved with a giant tree spade some years back. Sandy soil, but the top 5 feet was nice and dark. The area would have been forest and marsh only about 50-100 years ago.