How much biochar do I need to bury actually?

Rob Hopkins – co-founder of Transition Towns -has been to Sweden and a publicity event was arranged to effectively remove carbon dioxide from the atmosphere by burying biochar (charcoal made from burning wood with low oxygen supply to leave as much as 1/3 of the carbon.)

This is a great opportunity to do some maths – parents and children, school classes, local activists etc.

Put your answers in the comments section below.

The publicity says that every Swede needs to bury 17 kg of biochar a day. That is

17kg X 365 = 6 205 kg or 6.2 tons.

The Swedish EPA – Naturvårdsverket-  estimates that Sweden emits about 100 million tons of carbon dioxide equivalents from its total economic activity (Including import)

See the statistics here (in Swedish)

GIVEN that the above is true.

CALCULATE, in metric tons, the weight of  annual carbon dioxide emissions this represents for each Swede given that the Swedish population is 10 million.

CALCULATE in metric tons, the equivalent annual average emissions in carbon per person

Trees to wood to biochar

  • Newly harvested trees contain about 50% water.
  • Wood, when dried, has about 15% moisture in it.
  • Completely dry wood has about 50% carbon content in it.
  • When you char wood you loose about half of the carbon content of the wood.

GIVEN the above trees to wood ratios:

CALCULATE how much weight of  wood in tons, newly harvested, per Swedish inhabitant, is needed to make biochar to completely compensate emissions from Swedes.

CALCULATE the area of mature forest (in hectares) you would need to chop down to get that wood (you may need to search the internet for figures)

Forests in Sweden have an average  117 m3 of wood per hectare.

Wood weighs about 400 kg per cubic meter


GIVEN THAT SWEEN HAS 28 million hectare forest

CALCULATE the percent of Swedish forests that should be felled and biocharred each year to fully compensate emissions.

Do feel free to comment on your findings in the comments section.




You will probably need to use our data bank of basic conversions here.

2 Responses to “How much biochar do I need to bury actually?”
  1. Susanna says:

    Very interesting experiment! I hope l am wrong, but according to my calculation 38% would be needed, each year. Too much..
    What is the potential if we use the organic residues from both forestry and farming?

    (6,2 ton biokol per år =12,4 ton kol i helt torkad ved = 24,7 ton helt torkad ved = 49,4 ton ny skördad ved = 124,25 m3 nyskördad ved= 1,06 ha. * 10 milj= 10,6 milj ha = 38% av Sveriges skogsareal.)

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