## How much carbon dioxide can a giant sequoia store?

**Below you will find our calculations in detail for the assertion that the General Sherman Giant Sequoia has stored over a full human lifetime of carbon dioxide emissions.**

**Note: we use American mathematical nomenclature here (commas to separate 1000s, periods to indicate decimals) with metric units**

When calculating carbon dioxide sequestered by a sequoia, it is first necessary to have the density of sequoia wood (we didn't want to harm our sequoias). We did also receive a generous sample of sequoia wood from our friend Joe Welker at giant-sequoia.com (where we bought our sequoia trees). The measured density for a small piece of sequoia wood containing bark was approximately 0.48 g/mL. We obtained this by measuring a small piece of sequoia wood (36 grams) on a very accurate scale. We then submerged this same piece in a graduated cylinder, which displaced 75 mL. 36/75 = .0.48g/mL which equals 0.48 g/cc as one milliliter is equal to one cubic centimeter, by convention.

This density of 0.48 g/cc is within the range of densities reported by Wolfgang Knigge in his scientific paper

*Giant Sequoia in Europe*, http://www.fs.fed.us/psw/publications/documents/psw_gtr151/psw_gtr151_06_knigge.pdf

*.*His reported densities found average values of 0.345 g/cc in European giant sequoias (with a range of 0.180 to 0.600 g/cc) and 0.369 g/cc in (with a range of 0.279 and 0.671 g/cc) California giant sequoias. Our density of 0.48 g/cc converts to 480 kg/m3 . The math for this conversion is 0.48g/cc x 1,000,000 cc/m3. This result is then multiplied by 1 kg/1000 g, equaling 480 kg/m3.

Next we need to calculate how much mass the largest living sequoia tree, General Sherman, contains. According to the National Park Service, the General Sherman sequoia has a volume of 1,486.6 cubic meters (http://www.nps.gov/seki/learn/nature/sherman.htm, http://www.livescience.com/29144-worlds-largest-tree.html). To get total mass of this tree, we multiply 1486.6 m^3 by 480kg/m3. This gives us a total mass of 713,568 kg for General Sherman.

This mass is of course not all carbon - much being oxygen, nitrogen, and other elements. Most trees are about 50% carbon by mass. However, as giant sequoias have more heartwood (more durable wood in the center of the trunk) than sapwood, and heartwood has a slightly higher carbon content, this 50% value may be too low for sequoias. According to Sean Thomas in his Paper

*Carbon Content of Tree Tissues: A Synthesis*(See section 4.1, available here: http://www.mdpi.com/1999-4907/3/2/332/htm), giant sequoias are approximately 55% carbon by mass. When we multiple our calculated mass for General Sherman of 713,568 kg x .55, we get a carbon mass of 392,462 kg.

We next need to convert the mass of carbon into metric tons, so we divide 392,462 kg by 1000 to get a value of 392.4 metric tons or carbon stored in General Sherman.

However, carbon is not the same as carbon dioxide. Carbon dioxide has one carbon atom and two oxygen atoms per molecule. Trees absorb the carbon when growing while (mostly) emitting the oxygen. The atomic weight of carbon is 12.001115, while the atomic weight of oxygen is 15.9994. So the total atomic weight of CO2 is 43.999915. With a little algebra, we see that since the ratio of carbon dioxide to carbon is 43.999915/12.001115 or 3.6663 units of carbon in the tree for every unit of carbon dioxide removed from the atmosphere. We obtained this information from the Broward County Florida Climate Change website (https://www.broward.org/NaturalResources/ClimateChange/Documents/Calculating%20CO2%20Sequestration%20by%20Trees.pdf) as well as contact with Richard Campbell from Save The Redwoods.

We can thus multiply our total mass of carbon, 392.462 tons by our conversion factor 3.6663 from above to get 1438.892 total tons of CO2 removed by the General Sherman giant sequoia.

Americans, on average, produced 16.6 metric tons (or tonnes) of carbon dioxide per year in 2013 (the most recent year available) according to the Netherlands Envirornmental Assessment Agency (Table A1.2, page 49 found at http://edgar.jrc.ec.europa.eu/news_docs/jrc-2014-trends-in-global-co2-emissions-2014-report-93171.pdf).

When we divide 1438.892 metric tons of carbon dioxide removed by General Sherman by 16.6 metric tons, we get 86.7 years of CO2. That is 86.7 years of carbon emissions sequestered in a single tree! We find this number so impressive that we checked our math several times.

Life expectancy for Americans, according to the Centers for Disease Control, is 78.8 years as of 2014 (http://www.cdc.gov/nchs/fastats/life-expectancy.htm).

Caveats: General Sherman is the largest sequoia now living, and any trees planted would be unlikely to get quite this large. We chose this tree as good data was available on its volume. Also, it likely took several hundred years to reach this size, with more carbon absorbed more quickly at larger sizes. So any sequoias planted are unlikely to absorb a whole person's carbon dioxide output for several decades. However, adults emit considerably more carbon dioxide than young children, so the growth and sequestration of a sequoia may roughly mirror a human's emissions. However, sequoias are likely to grow faster in the higher carbon dioxide now prevailing (which will only accelerate absent intervention).

Also, as mentioned elsewhere, above ground volume of a tree does not take into account volume of roots still living below a tree, carbon based fungus (mycorrhizae) living off those roots in a symbiotic relationship, or humus previously produced by that tree, all of which store carbon.

Please contact us with any questions or comments at matthewauman@dewharvest.com