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Comment by danmaz74 | Hacker News Reader

I really wonder why, when talking about climate change, the reference to deforestation has been downplayed so much compared to a few years ago. Isn't that just as important as CO2 emissions?

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Did some programming on the Kyoto accord. At the time, old forests were thought to be carbon neutral (e.g. in a steady state), while a growing forest clearly absorbs carbon, and we assumed cut trees were released carbon into the atmosphere.

I am curious about the last assumption: Wood products can hang around for quite a while, so while long-term decomposition may release their carbon into the atmosphere, in the short term we have some very old wood around. Hell, maybe we could grow trees and sink them into oxygen-deprived water where they never decay.

Ultimately investment in this area has been reduced as the truth could be very inconvenient for the economies that rely on tree farming or land created by deforestation. See the disgraceful yellow blob: https://en.wikipedia.org/wiki/Kyoto_Protocol

> I am curious about the last assumption: Wood products can hang around for quite a while, so while long-term decomposition may release their carbon into the atmosphere, in the short term we have some very old wood around.

I have a hard time thinking of significant amounts of wood that doesn't decompose, unless treated by humans. There are exceptions, including petrified wood or maybe wood in oxygen-deprived water (I don't know much about that) but I doubt it adds up to much. I know I've read studies about the carbon released by decaying organic matter in rivers and river deltas; it's a well-studied process as far as I know.

Not to nitpick but because this is really cool: petrified wood is actually stone.

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

What about architecture? There are plenty of buildings which have lasted over 100 years.

> What about architecture? There are plenty of buildings which have lasted over 100 years.

Agreed. That's what I was thinking of to when I wrote, "unless treated by humans".

Ah, I was thinking of pressure-treated wood [0][1] as opposed to "raw" wood.

[0] http://www.homedepot.com/c/discover_benefit_pressure_treated...

[1] http://www.strongtie.com/productuse/ptwoodfaqs.html

Thanks, great answer!

I'm following the CO₂ emissions discussion less closely than I should, but agricluture generally (broadly scoped, including forestry) is a major contributor. Soil has considerable carbon content, and that can be and is released through human activity and disruption.

Livestock account for 18% of CO₂ emissions, agricluture 8% (75% of that from production of ag chemicals -- pesticides and fertiliser).

US EPA gives 9% of total CO₂ emissions as from agriculture:

http://www.epa.gov/climatechange/ghgemissions/sources/agricu... http://www.epa.gov/climatechange/images/ghgemissions/sources...

Nature puts the level at ⅓ worldwide:

http://www.nature.com/news/one-third-of-our-greenhouse-gas-e...

Deforestation: 6-17% of anthropogenic CO₂ emissions: http://www.nature.com/nclimate/journal/v2/n3/full/nclimate13...

The problem with deforestation isn't just the CO2 emission, but, most importantly, the missed future CO2 absorption. At least, that what I was thinking about.

Grown forests are carbon stores, not carbon sinks: the carbon is locked into trees and released when the trees die (some of it might get sunk into the soil but IIRC it's a very small fraction). When the forest does not grow, its day-to-day carbon impact is pretty much neutral, growing trees are balanced by decaying dead trees.

There's limited "missed future CO2 absorption" to deforestation, but there's a huge "immediate" released of stored carbon.

I used to think old forests were carbon neutral but an argument prompted me to google, and I found this:

http://www.nature.com/nature/journal/v455/n7210/full/nature0...

http://www.scientificamerican.com/article/old-growth-forests...

http://www.sciencedaily.com/releases/2008/09/080910133934.ht...

Atmospheric carbon per area is about 1 kg/square meter. (x)

It's not inconceivable that trees could store roughly similar orders of magnitude of carbon per area.

  x: 0,3 * 5e18 * 400/1e6 / (7000000*7000000*4*3,14)

> but there's a huge "immediate" released of stored carbon.

Surely that depends on where the tree goes. If it's burned, or left rotting, sure. If it's harvested for building materials, might it not even lead to increase storage of carbon overall.

I think one of the biggest source of deforestation is "slash and burn" subsistence agriculture, so, definitely a CO2 source.

Building material harvesting very rarely the primary purpose of deforestation.

My recollection from school years is that the fraction that goes to the soil is significant, but I don't know about more recent data...

> Soil has considerable carbon content, and that can be and is released through human activity and disruption.

None of your numbers suggest that carbon from soil is significant. The vast majority of carbon involved with agriculture comes burning fuel or from plants (such as when cows eat them and emit gas), and the carbon in plants comes from the air.

Quite honestly, I don't have the numbers I'd like on this. But you're talking about topsoil, which covers literally hundreds of millions of acres throughout the US, and probably on the order of billions of acres worldwide. And that for a depth of up to multiple meters. That's a vast, vast resource. And soil depletion is about exhausting that -- both returning the carbon content to the atmosphere and washing away topsoil.

OK, here's a Wikipedia stat:

Soil carbon is the generic name for carbon held within the soil, primarily in association with its organic content. Soil carbon is the largest terrestrial pool of carbon, containing 2,200 gigatonnes (Gt) of it.[1] Humans increasingly influence the size of this pool. Soil carbon plays a key role in the carbon cycle, and thus it is important in global climate models.

Citing: Batjes, N.H. (1996). "Total carbon and nitrogen in the soils of the world". Soil Science 47 (2): 151–163. doi:10.1111/j.1365-2389.1996.tb01386.x.

Continuing:

Although the figure is frequently being revised upwards with new discoveries, over 2,700 gigatonnes (Gt) of carbon is stored in soils worldwide, which is well above the combined total of atmosphere (780 Gt) or biomass (575 Gt), most of which is wood. Carbon is taken out of the atmosphere by plant photosynthesis; about 60 Gt annually is incorporated into various types of soil organic matter (SOM), including surface litter; about 60 Gt annually is respired or oxidized from soil.[2]

And I really don'tknow how that is influenced by human activity, climate change, changes in biocover, etc.

There's also loess, a high-carbon sediment covering 10% of the Earth's surface, to depths of tens of meters, over 100 meters in parts of China.

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

More on CO₂ in soils: http://soilquality.org.au/factsheets/how-much-carbon-can-soi...

Deforestation is a form of CO2 emission: a stable forest is roughly carbon-neutral (over long time scales obviously), a growing forest locks up carbon, a shrinking forest releases carbon.

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