Monday, April 16, 2007

Carbon-based life forms

So here's the scoop on carbon sequestration.

We burn fossil fuels to produce energy, and the byproduct of this process is the rapid release of carbon dioxide into the environment. Carbon dioxide is the principal greenhouse gas that contributes to global warming. Global warming is part of our overall global climate change, which has devastating consequences such as the melting of the polar ice caps and subsequent rising of the oceans, affecting weather patterns around the world. We can offset our own carbon dioxide emissions (driving our car, heating our house, buying our food) by carbon sequestration.

"Carbon sequestration refers to the provision of long-term storage of carbon in the terrestrial biosphere, underground, or the oceans so that the buildup of carbon dioxide...will reduce or slow." (1)

A carbon dioxide (CO2) sink is a carbon reservoir that is increasing in size, and is the opposite of a carbon "source". The main natural sinks are (1) the oceans and (2) plants and other organisms that use photosynthesis to remove carbon from the atmosphere by incorporating it into biomass. This concept of CO2 sinks has become more widely known because the Kyoto Protocol allows the use of carbon dioxide sinks as a form of carbon offset." (2)

Here in Minnesota we can preserve and create carbon sinks by protecting and planting forests and prairies. Native plants are better adapted to our soil profile and climate, as well as having natural pest and disease resistances.

On the individual scale, Scientist Jonathon Foley has been creating a carbon budget alongside his financial budget. He and his family have reduced their carbon dioxide footprint as much as possible, including using energy efficient appliances and moving closer to work, as well as getting rid of a car.

"Every square meter of forest, Foley says, stores 10 to 15 kg of carbon in biomass above ground and 10 to 15 kg in the soil. A prairie stores only three kg above ground, but 30 to 40 below. Midwest soils are deep and fertile because the prairie built up humus there for millennia. Prairie restoration is a popular community activity around Madison, so the Foleys will help do the work and also contribute money to prairie and tree planting groups." (3)

Jonathon's brother David has taken up organic gardening. When David and his family first began, the soil tested at only 1 percent organic matter. Now it's at 7.7 percent, about double your average farm soil. His brother Jonathon runs the numbers for him to see how much carbon he has offset.

"A silt-loam soil, Jonathan says, weighs roughly 85 pounds per cubic foot. Eight inches of it weighs 56 pounds per square foot.

Organic matter is about 58 percent carbon. So soil with 1 percent organic matter contains (hmmm, 1 percent of 58 percent of 56 pounds) 0.3 pounds of carbon per square foot. Soil with 7.7 percent organic matter contains 2.5 pounds of carbon per square foot. David and Judy have increased the amount of carbon in every square foot of their garden by 2.2 pounds.

It's a big garden, 0.4 acres. (Actually it's a communal garden, which David and Judy share with their neighbors.) That's 17,424 square feet. Multiply by 2.2 pounds of carbon per square foot -- let's see here -- that makes over 38,000 pounds of carbon removed from the atmosphere -- 19 tons!

Jon writes to David: "You have sequestered 19 tons of carbon into your garden over the last 10 years. If you think that the soil test is representative of a deeper soil profile (let's say 16 inches instead of 8), then scale that number up. This is impressive! The average American releases 6 to 6.5 tons of carbon into the atmosphere each year. So you have offset about three years of an average American's emissions." (4)

Obviously this is only part of the solution. Fossil fuels are non-renewable, and Peak Oil is just around the corner (or maybe it's in the past). But by reducing the use of fossil fuels and increasing our use of renewable energy sources like wind and solar we can certainly take a giant leap forward.

If the average American can reduce their consumption by 50%, down to 3 tons of carbon per year, they would have to plant the equivalent of about 15 trees a year. At 20 to 30 kilograms of carbon storage in a cubic meter of an average forest vs 33 to 42 kilograms in an average cubic meter of prairie, prairie plantings are 40% to 65% more effective then tree plantings in the storage of carbon in terms of area. Given the chthonic perennial nature of the biomass of a prairie vs. the terrestrial linear expansive nature of a forest, prairie plantings would fit into the urban niche better then forest gardens.

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