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Where's the carbon?

In the terrestrial carbon cycle, carbon moves from the atmosphere, to vegetation via photosynthesis in the form of complex carbon compounds (plain C in the animation), to litter and soil when the plants or leaves die, and back to the atmosphere as carbon dioxide via decay, oxidation, or burning.

The approximate pools of carbon are indicated in gigatons (billion metric tons). These carbon pools are broad averages, and are proportional to the average residence time of carbon in them. The terrestrial carbon cycle is an emergent phenomenon, the sum of the metabolisms of countless self-motivated organisms, most of them microscopic.

Human management influences both the biomass pool and the soil pool, either shortening or lengthening the time that carbon spends in each. Human management of soil and vegetation thus has great leverage on the atmospheric pool.

Fossil fuel burning (not shown) also contributes carbon dioxide to the atmosphere, about a tenth of the total terrestrial circulation.

From a forthcoming animation on the carbon cycle. Figures are from Rattan Lal, Sequestration of atmospheric CO2 in global carbon pools, Energy and Environmental Science 1:86-100 (2008).


Nice work, Peter! I recognize the diagram from your talk at the 'Black' swan in Vancouver.

A couple things that caught my eye: It has that nice friendly feel - the fluffy cloud, or the little face in the woods, for example. :) I think I'd like to see caps and units on the constituents though (e.g. Air (780 gt C)) and I think it would help differentiate the visuals if you changed the colour of the line drawing in Vegetation to white, and have the white colour continue through to the root system in the Soil section.


Thanks Dave, done. Good eye.

Austin, Texas

I like this graphic very much! I would like to see percentages attached to the 3 portions as that may help quickly reinforce one of the fundamentals with another communications style.

Can do Christina, but the pie chart slices will be moving in the final version. First, seasonal variation in the biomass pool (the up and down seasonal zigzag of the Keeling curve of atmospheric CO2). Second, a hoped-for increase in the soil carbon pool.

(Some recent studies indicate that Arctic soil carbon and peat may have been underestimated.)

The diagram is a curious hybrid. It's a pie chart, but also a clock, showing the portion of time in which carbon bonds are available for doing biological work, and when they are just idly heating the planet as CO2. The diagram is also a landscape, suggesting perhaps that the way to enhance the cycle is to get the bare soil on the left side covered with vegetation and litter.

Hi Peter,

V impressed with your diagram, and with the Soil Carbon Slideshow. I have just prepared a blog post drawing attention to the work of the Soil Carbon Coalition, and have embedded them there.

This seems to be something that you encourage, but if you have any objection please do just let me know. My post is up at:

Very best wishes,

Yes, we encourage this.

Thanks Peter. Maybe I missed it, but I couldn't find any official notice to this effect on the site. You might consider including an appropriate Creative Commons tag on your site, to encourage more spreading of your work:

that fluffy moving diagram is nonsense: there is some 50X as much CO2 in the oceans as there is in the air.

Note that this is a diagram of the terrestrial (land-based) carbon cycle. The ocean, which contains vastly more carbon than soil, biomass, and air combined, exchanges carbon with the atmosphere via solubility, so in many ways it can be considered an extension of the atmospheric pool.

Ocean buffering is one reason why reducing fossil fuel emissions has little near-term leverage on atmospheric carbon.

This diagram does not include rocks, either, which hold far more carbon than the ocean.

so if the oceans are "an extension of the atmospheric pool" (surely the other way round?) then why is it not shown?

it seems to me that your diag is a kind of devotional exercise rather than an attempt to explain anything.