A fabulous science lesson

okay, so again, I recently produced this little spoof/promo video:

And I got to chatting with a real live professor of Ecology and I asked him, "well, it's just a spoof of propaganda ads, but is this, like a plausible idea?"  and he (Eric J. Olson of Brandeis) was kind enough to provide this very interesting and enlightening explanation!  And here it is!  Thank you Eric! 

Me: 
I have to ask this question: is it theoretically possible, to
grow fast growing trees, them cut them down and store them in yucca
mountain, and recapture carbon emissions that way??? 

Eric:
Yep, theoretically.   But remember, trees do not live on CO2 and water
alone.   They also take nitrogen, phosphorus, potassium, magnesium, calcium, iron,
sulfur, and so on from the soil.   Nitrogen, phosphorus and potassium in
atomic abbreviation terms are N, P, and K, and this is what most farmers buy every year at the fertilizer store to feed the fields where they grow corn and wheat and all the other crops that feed the world.   The reason we have to do this is we
harvest the plant material (its called the crop in agriculture) and send it
off to feed humans and cows and chickens and even our pets.  

We humans and our domesticated animals then use the nutrients like N and P and K (and iron from spinach and potassium from bananas) to grow and to live.   So the nutrients that make our bodies start in the soil and we need to replenish them by adding fertilizer.

So the notion of harvesting fast growing trees or other plants and then storing the trunks and branches in a deep underground deposit raises the question, what about
replenishing of THOSE soils?   If trees became a fast crop like vegetables
and grains are today, we would likely see their yields (tons per acre per
harvest) come down over time.   We' d have to start fertilizing soils just
to grow trees, this is not currently done because fertilizers are too
expensive to justify something that has such low value as lumber (remember
we only harvest lumber now on about a 30 year rotation, at the least, so the
annual value of the next ring of wood is pretty small).   So now we are just
going to grow trees and store them, not use them – who will pay?   Because
if we fertilize the soil to do this, there will be a cost to growing all
those trees.

Better might be to burn the fast growing plants we grow and use them in
power plants instead of coal — this way the CO2 taken in the by plant one
year is released the next but if you replant the field you take that same
CO2 back in.   It becomes a cycle instead of what we have now — taking coal
from the ground, which is storage of CO2 about 300 million years old, and
releasing ancient carbon.   Impossible to make a cycle from coal, it takes
so long to make new coal (and huge amounts of compression from the earth).

But won't these soils also become depleted as well?   Yes, but if you were careful about it, you would be able to use the ashes from the combustion process to return some of the nutrients — and maybe you could put in filters on the smokestack to capture some of the nutrients that would otherwise be lost in the smoke.    If this ash (which should be pretty light in weight) were shipped back to the farms to be spread as a fertilizer, you would complete that loop too.   By they way, the food crop equivalent is if human feces were to be processed back into fertilizer, poop is equivalent to the "ashes" of our bodily combustion process!

If the idea of burning fast growing plants instead of coal seems ridiculous
well hang on to your hats pardner, because that future is now:

http://greeninc.blogs.nytimes.com/2009/10/01/utility-replaces-some-coal-with-swtichgrass/

Cheers,

Eric

Eric J. Olson
Senior Lecturer in Ecology
Program in Sustainable International Development
The Heller School for Social Policy and Management
Brandeis University
415 South Street
Mailstop 035
Post Office Box 549110
Waltham, MA 02454-9110