Kyle,
On 11/9/2012 12:09 AM, Takamoto wrote:
Dear List and Chanakya,
Thanks for the detailed answer. But I was thinking, shouldn't you
add those two numbers because biogas both reduces Methane emissions
from open pit composting AND reduces unsustainable CO2 emissions
from cooking with firewood. Its not an either/or situation, right?
To a degree, the answer both to your original question and the above
depends on context and intention. It is one thing, for example, to
have a number that can be used in casual conversations such as those
on this list, and another to have a number that one expects to submit
to the UNFCCC as a basis for a claim on CER carbon credits, or Gold
Standard carbon credits. In a third instance, one may be exploring the
development of a climate model, and addressing questions such as yours
in the attempt to come up with numbers that assist in predictions of
outcome.
Obviously neither context nor intention would have any impact on the
situation itself-- our mere point-of-view does not change the world--
but both would have a significant impact on the approach taken.
Just as an example of how much these things might vary, consider that
in terms of CO_2 equivalence or global warming potential (GWP), the
impact of a tonne of methane can be taken as (that is, some common
equivalences mentioned in various sources are) 20 tonnes CO_2 , 27
tonnes, or 100 tonnes. These are variously quoted for several reasons
besides simple error. The two most common reasons are that research
has gotten better on this question, somewhat changing the number
known, whereas the number as used in some calculations depends on
convention, and the convention has not caught up with the research. As
well, this number depends on the time scale being considered, because
methane degrades over time in the atmosphere by reaction with oxygen. Thus
"...the 20 year GWP of methane is 72, which means that if the same
mass of methane and carbon dioxide were introduced into the
atmosphere, that methane will trap 72 times more heat than the
carbon dioxide over the next 20 years." (Wikipedia, Global-warming
potential <http://en.wikipedia.org/wiki/Global-warming_potential>)
Whereas most people are not aware, the GWP of 25 to 27 commonly quoted
for methane is its effect averaged across a century.
I mentioned "convention", above, and that should not be taken as a
criticism of some agencies or methods. Rather, convention is
significant for such things as doing calculations for carbon credits,
since there is a matter of justice to be considered-- all those who
previously submitted did so on the basis of what was known at the
time, resulting in their use of a certain factor. Now that better
information is in hand, should the number used be changed, providing a
relative advantage or disadvantage to those who submit subsequently?
So unfortunately in order to gain a fully serviceable answer to your
question, you would need to specify a bit more exactly.
There is a final issue I would mention, and it is that even with a
clear context, a known intention and a vetted process, one of the very
peculiar things that will always be true about calculations of CO_2
reductions is that we can never actually measure such reductions.
After all, what one is asserting is an /estimate/ of what /might/ have
happened, except that we, or the population being studied, are not
doing that thing that might have happened. It is, ultimately, for this
reason that calculations done when seeking carbon credits tend not to
add all potential reductions together. Dr. Chanakya would have to
answer for himself, but it may well be that he is used to calculating
for the purpose of asserting for CERs. The convention used is to be
rather humble about the estimate of savings, in which case one might
take the approach of choosing between savings from open-pit composting
that did not happen, and savings from wood that was apparently not burned.
For further information about calculations made in such situations, I
would suggest visiting the UNFCCC CDM site (here
<http://cdm.unfccc.int/>), searching for (here
<http://cdm.unfccc.int/Projects/projsearch.html>) and reviewing some
of the submissions made.
d.
--
David William House
"The Complete Biogas Handbook" |www.completebiogas.com|
/Vahid Biogas/, an alternative energy consultancy |www.vahidbiogas.com
|
|
"Make no search for water. But find thirst,
And water from the very ground will burst."
(Rumi, a Persian mystic poet, quoted in /Delight of Hearts/, p. 77)
http://bahai.us/
|
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