Comment by Merovius | Hacker News Reader

Comment by Merovius | Hacker News Reader

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> 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 numbers in percentages of photosynthesis at all - you multiply both sides of the equation). And b) then proceeds to pretend that the Amazon eats up most of the Oxygen it produces, but the rest of the world apparently doesn't. Like, if a tree re-metabolizes 40% of the O₂ it produces, then that's also true for the 91% of O₂ produced outside the Amazon, so we still end up with the same 9% figure of all O₂ produced in the Amazon.

The article ends with the "CO₂ emission is more important". Which, again, fair. But Photosynthesis is presumably a pretty important mechanism by which CO₂ is removed from the air. So a reduction of O₂ production is equivalent to a reduction of CO₂ absorption (though you have to multiply with 2.67, don't forget!), which seems to… be a bad thing for CO₂ concentration in the air.

The gist of the article is pretty much "if you don't round and take into account maritime photosynthesis, the Amazon only produces 9% of all O₂". Which is fair. The rest is noise. It doesn't add to the argument and is just fueling the "MSM is bad!" cries…

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.

It could be correct and still have an impact on CO2 levels as it is still a massive sequester of carbon. Burning it down removes the sequester and adds it to the atmosphere.

Also, just because it doesn’t produce the breathable O2 we need, that doesn’t mean it’s not part of a global system that produces and stabilizes our atmosphere. It actually is responsible for a massive silt run off that feeds the oceanic diatoms that in turn produce half of the worlds breathable O2 and fixes carbon right in the ocean.

This is a case where a literal point is incorrect but it does not decrease the importance of the rainforest to our globe.

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 this seems correct. Extracting fossil fuels releases all the carbon sequestered by organisms over 100 million+ years. Burning down a rainforest only releases the carbon sequestered by organisms currently living.

I don't see how it wouldn't be possible for fossil fuels not to contain orders of magnitude more carbon than forests. Which is of course why the switch from wood to coal precipitated the industrial revolution.

[1] https://medcraveonline.com/FREIJ/FREIJ-02-00040.pdf [2] http://mentalfloss.com/article/63519/how-many-trees-are-ther... [3] https://ourworldindata.org/co2-and-other-greenhouse-gas-emis...

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 plants also sequester. It’s also a home of biodiversity and nutrient run off that assists other parts of our global ecosystem. In turn, Carbon sequestration occurs over time; and it’s these rich, biodiverse ecosystems that produce the fossil fuels that we are burning, without them the carbon would never sink into the earth as it does.

Eliminating the rainforest halts the engine that cleans the atmosphere and removes the carbon and cools the earth. It would also dump millions of more tones into the atmosphere (even by your calculations). It would also disrupt global food chains which do produce our global breathable oxygen.

I’m not sure what your point is that you are making other than you imply that we don’t need to save the tropics because fossil fuels are worse; but I heartedly disagree with that implication.

> 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.

> Trees are not the only place carbon is sequestered in a forest

Trees are not the only part of the amazonian ecosystem, but I'm pretty sure trees outweigh other parts of the amazonian ecosystem by a significant ratio. I think the calculation probably suffices as a back of the envelope estimation.

> I’m not sure what your point is that you are making other than you imply that we don’t need to save the tropics because fossil fuels are worse; but I heartedly disagree with that implication.

Removing tropical rainforest would be disastrous, but not because of impact on global CO2 levels. (Its effects on CO2 levels would not be helpful but wouldn't be among the worst consequences). Among other reasons, it would significantly alter global weather patterns and cause massive damage to ecosystems across the globe.

I think the point is that even an ecosystem as massive and influential as the amazon can't even make a dent in the amount of CO2 that is being produced by human activity.

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.

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