You just did a typo somewhere 
33 MJ/kg = 33,000,000 J/kg = 33,000 J/g = 33 J/mg
So for 100 Watts, your approach will give 3 mg (milligrams) of carbon per second, which is comparable order of magnitude wise.
On occasion, while walking through a wooded glen, I’ll think, “This is my church.” So maybe the answer to the OP is as simple as “forests.” Forests are where trees go for mass! 
(Reformed ex-catholic scurries away from thread…)
Where do trees get their mass?
Catholic and Episcopalian Ents simply go to the nearest church or cathedral. They just have a problem getting through the door.
Thanks; I feel lighter and more energetic now. 
Trees get their mass from the Higgs boson. Bigger trees get their mass from bigger bosons.
Well, a tiny fraction of it, anyway. Most of their mass, they get from the binding energy of the strong nuclear force, a process completely unrelated to the Higgs field.
My guess was that [Senegoid](Straight Dope Message Board - Your direct line to thousands of the smartest, hippest people on the planet, plus a few total dipsticks.) was making a pun from “bigger bosoms.”
While removing carbon from the atmosphere is obviously a nice thing, I’ve read that trees are essentially carbon neutral when it comes to climate change. That’s because the carbon is rereleased into the atmosphere when the tree dies and decays.
Well, actually I was more thinking like “bigger boatswains”.
That’s true when forests are in a steady state. The problem is that so many trees have been removed (and are being removed) and not replaced, especially for agriculture. Less carbon in storage in trees means more carbon in the atmosphere.
It has to be, unless some of the carbon is going to other compounds. Which it might be, for the slowly-decomposing tree.
Over the long term, yes. However, some of the carbon in the decomposing tree will be incorporated into the biomass of fungi, bacteria, termites, and other decomposing organisms that feed on it. So some of the carbon originally fixed by the tree could remain in the ecosystem for a very long time, even after the tree itself has entirely disappeared.
The net amount of Carbon released would be the same. However some/lot of Carbon released during decomposition is released as Methane (CH4) versus (CO2). Each molecule of Methane is 28 times worse than CO2 when greenhouse effect is concerned.
But methane doesn’t tend to stay methane for very long, in an oxygen-rich atmosphere.
This is not my area of expertise, but from discussions IIRC the 28 number there is the average over 100 years.
Did some digging around and this paper (Table 1) gives the same number as 34 (average over 100 years) Fugitive Methane and the Role of Atmospheric Half-Life | SciTechnol
Because you aren’t burning elemental carbon. You are changing let’s say a glucose molecule into water and carbon dioxide. That process would have a different net energy difference.
Re: decomposition, obviously all the carbon doesn’t end up back in the air quickly because soil exists. There’s more carbon in soil than there is in the atmosphere.
τ ~ 12 years, t1⁄2 ~ 9 years. Hence the GWP depending on time scale.
IPCC GWPs are listed here:
28 vs 34 depends on whether feedbacks are considered. And of course if one is concerned about temperatures in, say, 2040, the 100-year GWP is less relevant.
Hm, that’s longer than I would have expected.