# The Naked Scientists Forum

### Author Topic: How much CO2 does a tree consume per year?  (Read 57135 times)

#### alancalverd

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##### Re: How much CO2 does a tree consume per year?
« Reply #25 on: 06/01/2014 16:12:50 »
But this is not 'new' CO2 is it.

There is very little "new" CO2 in the atmosphere. Every carbon atom in fossil fuel was previously in the atmosphere, thence absorbed by plants to make coal or via plants and animals to make oil and gas. The only "new" stuff comes from volcanoes.

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I'm sure that you wouldn't want to give the impression that just through respiration, humans (or any other animals for that matter) cause an inherent increase in the amount of 'free' CO2 in the atmosphere (and ecosystem as whole), would you?
Of course they do. Remember Biology 101? Plants absorb CO2 and emit oxygen. Animals eat plants, inhale oxygen, and exhale CO2. That's life. The quantity of CO2 in the atmosphere at any time (until Mankind discovered fire) depends on the ratio of plants to animals, and it has only recently exceeded the previous peak level reached some 320,000 years ago.

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Increased numbers of humans are in no way directly, by breathing, putting any more CO2 into the system.
Nonsense. Humans are animals, animals exhale CO2, so more humans = more exhaled CO2.

If you do the calculation based on the energy released by combustion of food (to produce mostly CO2 and H2O) you will find that human breathing at 10 megajoule/man.day accounts for about 10% of all anthropogenic CO2, and the animals that we farm for meat generate about 20 - 25% of the total. Furthermore, every molecule of "artificial" CO2 (from fossil fuels) is emitted to satisfy the demands of a human being, so fewer people = less CO2.
« Last Edit: 06/01/2014 16:22:33 by alancalverd »

#### alancalverd

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##### Re: How much CO2 does a tree consume per year?
« Reply #26 on: 06/01/2014 16:21:24 »
A tree releasing 226 liters, more or less, of oxygen, with a human consuming 5-600 liters that same day. Using that it seems to need two trees per human, per day? Could be my conversions, it was late, but, I don't think it is.

The operative phrase is "more or less". Trees come in all sizes and activities. Probably a third of the trees in the UK are quite small, deciduous, fruit trees, which only photosynthesise for about half of the year, but trees in the tropical rainforest are huge, effectively evergreen, and transpire all year round. It's noticeable that one of our transatlantic correpondents refers to sequoia as typical trees. You probably think of Nordic conifers as typical, whereas all I can see from my office are temperate beech and sycamore trees which are currently dormant and leafless.

#### yor_on

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##### Re: How much CO2 does a tree consume per year?
« Reply #27 on: 06/01/2014 18:36:40 »
That's one way to look at it Alan. The other would then be to define it as a respiratory planet, breathing using photosynthesis, being in a equilibrium. Then came the industrial revolution, two hundred and fifty, to three hundred years ago, that now has spread all over the world, in where we dig up the stored carbon, oil, methane, etc, changing that equilibrium, introducing a ever growing excess of CO2. Methanes rest product will also be CO2.
=

Although there is more to it than that. The populations world wide has grown as I understands it, from around 700 millions in 1700 to https://en.wikipedia.org/wiki/World_population_estimates

Around 7 billions today That's 7 000 000 000 people.
It also seems as six of those 'new' billions has come to be in the last hundred years, or less.

There has to be a limit to what Earth can adapt too, and I think we're near it, in so many ways. And this time I don't think war can 'solve it' for us. It will only make it worse, like the last man standing on a (probably radioactive) garbage heap, telling himself that 'he won'. Sort of really stupid thinking that one..
« Last Edit: 06/01/2014 19:05:45 by yor_on »

#### yor_on

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##### Re: How much CO2 does a tree consume per year?
« Reply #28 on: 06/01/2014 19:16:24 »
On the other hand. This is what a free market economy, combined with the idea that 'the market knows best' and some normal greed will lead to. The instruments for it being the modern assembly line, and automation, enabling industries to spew out products, and also to reap the benefits of raping the environment in a ever faster pace. What protects this idea is banks and corporations in where no holder of stocks really can be hold responsible for the corporations action. It limits all involved responsibilities, instead letting their personal greed, and the corporations need of profit, set what limits there might be, and so called 'ethics' :)

There are no ethics to that.

#### Bored chemist

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##### Re: How much CO2 does a tree consume per year?
« Reply #29 on: 06/01/2014 21:58:53 »
Trees are mainly made of wood and water.
The water gets sucked up from the ground and doesn't make any difference to the oxygen produced.
The wood is mainly  (about 75%) carbohydrates (cellulose and hemicellulose etc).
About a quarter of it is lignin.
(from here)
http://www.ipst.gatech.edu/faculty/ragauskas_art/technical_reviews/Chemical%20Overview%20of%20Wood.pdf

Lignin also isn't a hydrocarbon (though it does have a little less oxygen pro rata than cellulose)

So, to a fairly good approximation the reaction you need is
n CO2 + n H2O --> (CH2O)n + n O2
each molecule of CO2 produces 1 molecule of oxygen
So 44 grams gives 32 grams
48 pounds gives 35 pounds

Now, does anyone have a credible answer to the question where does the other 225 pounds of oxygen comes from?
If it's from making leaves, then the tree must make a lot of them; 6.5 times more (dry weight basis) than it makes timber.
That's spectacularly inefficient.

#### CliffordK

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##### Re: How much CO2 does a tree consume per year?
« Reply #30 on: 06/01/2014 22:12:32 »
So, to a fairly good approximation the reaction you need is
n CO2 + n H2O --> (CH2O)n + n O2
each molecule of CO2 produces 1 molecule of oxygen
So 44 grams gives 32 grams
48 pounds gives 35 pounds
Using your formula, if you incorporate 12 lbs of carbon, you will release 32 lbs of oxygen.
Incorporate 48 lbs of carbon, you release 128 lbs of oxygen.

Still a little short from the original numbers.

I wonder if the OP accidentally doubled the numbers again.
128 lbs x 2 = 256 lbs.  We breathe O4, right?
« Last Edit: 06/01/2014 22:22:45 by CliffordK »

#### yor_on

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##### Re: How much CO2 does a tree consume per year?
« Reply #31 on: 06/01/2014 23:23:47 »
It's weird stuff :)
But interesting.

Heres another take on it. "A resting, healthy adult on an average, cool day breathes in about 53 liters of oxygen per hour. An average, resting, health adult breathes in about 500 mL of air per breath. This is called the normal tidal volume. Now, 150 mL of this air will go to non- functioning areas of the lung, called the "dead space." The average breath rate for this average person is 12 breaths per minute. So, the amount of air breathed in by the person which is available for use is 12 x (500 mL -150 mL) = 4,200 mL/minute. Multiply by 60 to get 252,000 mL/hour. That is, every hour, the person will breathe in 252 L of air. Now, on an average, cool, clear day, only 21% of that air is oxygen. So, 21% of 252 L is 53 L.

So, in an hour, the person breathes in about 53 L of oxygen." times 24? Or does this change when you sleep? It should, as well as it should change with what you are doing. But it's about the same number anyway.

Eh, not really :) The number I got here is about the same as the first one I got, but that was for two persons, per day (1000-1200 liters) Here we instead find it for one person, needing around 1200 liters oxygen per day. Or let's say a thousand to twelve hundred. It's pretty confusing. And considering that I got 82600 liter per tree, per year? Divided with 365 becoming  226.3 liters per day??

We now would need one tree to produce 1200 liters oxygen per day for one person, making the number 226 liters per day for a tree sux, real bad.

Then we come to leafs. I started with looking at plants.

"how much oxygen do plants produce in an hour. Actually, I have data for how much oxygen LEAVES produce in an hour: 5 mL. If your average plant has 30 leaves, then that would be 5 ml/leaf x 30 leaves = 150 ml/plant/hour.

So, if an average person needs 53,000 ml (53 l) of oxygen per hour, and the average plant produces 150 ml per hour, then 53,000/150 = 353 plants. Since these are round figures, let us just say that between 300 to 400 plants are needed to produce enough oxygen to keep a person alive in an hour.

Again, there are many assumptions: average leaf, average plant. Plus you will need to take into accounted oxygen production decreases as carbon dioxide concentration increases Assuming this hypothetical person is in a confined space with all these plants, the CO2 concentration will rise due to the person's expiration. This will inhibit the plant's photosynthetic rate. Oh, yes, do not forget we will need good amount of light and water, too.

wizkid"

==

The next question could then be, how many leaves exist on a 'average leafy tree'?
I don't know?
« Last Edit: 06/01/2014 23:41:49 by yor_on »

#### CliffordK

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##### Re: How much CO2 does a tree consume per year?
« Reply #32 on: 07/01/2014 00:13:30 »
I'm seeing different estimates, but the air you breathe in is about 20% oxygen.  The exhaled air is about 15% oxygen, or a difference of about 5%.

The exhaled CO2 is about 4%.

Since you don't eat trees (other than fruit)...  Perhaps one should consider how much CO2 gets converted into simple sugars and carbohydrates in fruit, vegetables, and grains (plus whole grasses consumed by livestock producing milk and meat).
« Last Edit: 07/01/2014 00:16:31 by CliffordK »

#### yor_on

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##### Re: How much CO2 does a tree consume per year?
« Reply #33 on: 07/01/2014 00:33:06 »
We could use the numbers Wizkid gives for defining how many leaves you would need though, assuming 5 mL, then divide that with 53000. That would give us 10600 leaves needed (per hour although in principle you can use this number for any and all hours if you get my drift).

Now, that seems possible for a tree to handle, I think? I've seen some numbers, from 30 000 up to where a mature, healthy tree might have 200,000 leaves? But I don't really know.
==

the more I look into it the more I prefer http://scrippso2.ucsd.edu/plots actually. There's so many variables involved in this, from what you do, age, condition, etc etc to how many leaves a 'average' tree might have, and as Alan pointed out, it definitely depending on where you get that 'average', from what Country and trees. Then you have seasonal changes and how much sun, soil, night activity versus the day etc. No wonder the figures seems to differ :)
« Last Edit: 07/01/2014 00:47:08 by yor_on »

#### Bored chemist

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##### Re: How much CO2 does a tree consume per year?
« Reply #34 on: 07/01/2014 20:53:25 »
You could estimate the amount of oxygen someone uses in a day from how many calories they use.
(You need some information or assumptions about their diet too, but you should be able to get a ballpark figure)

#### CliffordK

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##### Re: How much CO2 does a tree consume per year?
« Reply #35 on: 07/01/2014 22:16:11 »
Essentially all of what we eat came from plant photosynthesis in the recent past (or eating animals that ate the crops).

Having more babies means eating more crops, but it doesn't significantly impact the overall CO2 balance.

What affects the CO2 balance is digging up buried carbon, oxidizing it, and releasing it into the atmosphere, and to some extent burning wood, for example clearing rainforests to make cropland.

Of course, the more people, the more cars and energy demands.

#### alancalverd

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##### Re: How much CO2 does a tree consume per year?
« Reply #36 on: 07/01/2014 23:27:45 »
The average human uses about 1.5 kilowatts of "artificial" energy, nearly all of which comes from fossil fuels. The numbers vary enormously from almost 20 kW in such diverse places as Canada and Saudi Arabia to 200W or less in parts of Africa and some Pacific islands.

The average human burns about 115 watts of food energy. Some of this comes from plants but increasingly it comes from farmed animals. We maintain about 3 times our body weight of farm animals, and all warmblooded creatures have broadly similar metabolic processes, so the animals we eat burn about  350W.

Thus about 25% of all anthropogenic carbon dioxide comes from humans and farm animals.

#### norton94

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##### Re: How much CO2 does a tree consume per year?
« Reply #37 on: 22/10/2014 22:15:38 »
My son just asked me if it would be possible to select a plant/tree based on C02 consumption and O2 emission - essentially developing a hybrid that would be more efficient at the process.  Has this been attempted?

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##### Re: How much CO2 does a tree consume per year?
« Reply #37 on: 22/10/2014 22:15:38 »