[DenisM]

A few comments are saying that forests capture a lot of CO2.

But how could that be? If a forest doesn't change over thousands of years it cannot be accumulating carbon in any significant quantity. Or else where would that material go?

The Amazon trees are about as tall and wide today as they were 10,000 years ago, and only so many of them fit on a given area. If the amount of vegetation remains the same the only way for a forest to capture carbon would be to accumulate an ever-increasing layer of it under the forest floor. That would be a lot of combustible material accumulated over millions of years that Amazon was around, and I'm pretty sure it isn't there (otherwise certain people would be mining it already).

Amazon is not scrubbing carbon out of the air, and neither does any other forest of static size. The carbon has to go into the ground to remain sequestered.

[patmcc]

>>>A few comments are saying that forests capture a lot of CO2.

As you indicate, those people are incorrect. But a forest may contain a lot of C02, such that burning it all at once increases the amount in the atmosphere noticeably.

[cmrdporcupine]

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.

[DenisM]

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.

[cmrdporcupine]

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.

[DenisM]

Amazon has been around for 55 million years. Do you think we will find the topsoil to be 55,000,000 / 100 * 5 feet thick? I wager it went up to like 20 feet max in the first million years and hasn’t changed since then.

[Rebelgecko]

Doesn't burning the forest down release a good portion of that CO2?

[DenisM]

My point is that a standing forest doesn’t affect carbon levels. A growing forest or a burning forest does.

So a statement like “forests are scrubbing CO2 and help us against climate change” are false - a stationary size forest has no effect whatsoever.

For carbon to be sequestered it has to go into the ground and stay there.

[crimsonalucard]

https://wwf.panda.org/knowledge_hub/where_we_work/amazon/ama...

it's just less accessible but I'm pretty sure like any forest on the face of the earth, portions of dead animal and plant matter is getting sequestered into the ground while another portion is getting exhaled by animals eating the leaves or other animals eating the animals.

The stuff that's getting sequestered though is probably miniscule. At the timescale of our lifetime it may be negligible but I wouldn't know as I'm not an expert. Perhaps someone with the actual data can fill us in?

[shkkmo]

Well, just based on the linked article:

> A final point to make is that the atmosphere is awash with oxygen, at 20.95% or 209,500 ppm (parts per million). Carbon dioxide, by comparison, is around 405 ppm and rising by around 2-3 ppm per year, over 500 times less. Human activity (around 90% of which being fossil fuel combustion) has caused this concentration to drop by around 0.005% since 1990, a trivial amount. In parallel, the same activities have caused carbon dioxide concentrations to rise by by 37 ppm since 1990, or 10%. This is a much more substantial percentage because there is so little carbon dioxide in the atmosphere to begin with, so human activities can make a major difference. This is why we need to worry about the increase of carbon dioxide in the atmosphere (and its resulting impact on climate), and why we don't need to worry about running out of oxygen.

The 3 order of magnitude difference is the relevant bit of info.

So while it takes millions of years for the amazon to have an impact on )2 levels, impacts on CO2 levels happen on the time scale of thousands of years.

This is also why it makes more sense to be concerned about the CO2 being released by burning the Amazon than the oxygen consumed by the fire.

[DenisM]

Even if a tiny amount was sequestered each year over the course of 55 million years there would be a huge pile of carbon there. But it isn’t there, is it?

[OscarCunningham]

Has the soil under the rainforest been slowly getting deeper?

[abdullahkhalids]

There is. That's all the coal, oil and gas we burn.

[crimsonalucard]

my initial reply was a post about oil mining in the amazon...

Additionally tectonic plates move, 55 million years ago the amazon probably wasn't even there. Additionally oil found on land could've been produced by biomass under the ocean and vice versa it's all moving around all the time. Likely the oil found underneath the amazon could have been produced at a time where that tectonic plate was under water.

[justanothernoob]

You aren't accounting for the trees being living, growing beings. Asking how they capture CO2 is kind of like asking how we grab oxygen- it's in the air, we use it to fuel our growth and stay alive, and then it's CO2 when it leaves our bodies. It's the reverse for trees, I don't know if any significant amount of solid carbon would need to accumulate, as it forms the wood and the varies trees that grow and die.

[crimsonalucard]

A forest of constant size is not growing and therefore not removing any carbon from the air is this persons argument.