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Kyle,<br>
<br>
<div class="moz-cite-prefix">On 11/9/2012 12:09 AM, Takamoto wrote:<br>
</div>
<blockquote
cite="mid:4DCE166D-A25C-4A12-9FA2-8494913905BF@takamotobiogas.com"
type="cite">Dear List and Chanakya,<br>
<br>
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? <br>
</blockquote>
<br>
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.<br>
<br>
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. <br>
<br>
Just as an example of how much these things might vary, consider
that in terms of CO<sub>2</sub> 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<sub>2</sub>, 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<br>
<blockquote>"...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, <span
dir="auto"><a
href="http://en.wikipedia.org/wiki/Global-warming_potential">Global-warming
potential</a>)</span></blockquote>
Whereas most people are not aware, the GWP of 25 to 27 commonly
quoted for methane is its effect averaged across a century.<br>
<br>
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?<br>
<br>
<br>
So unfortunately in order to gain a fully serviceable answer to your
question, you would need to specify a bit more exactly.<br>
<br>
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<sub>2</sub> reductions is that we can never actually measure such
reductions. After all, what one is asserting is an <i>estimate</i>
of what <i>might</i> 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.<br>
<br>
For further information about calculations made in such situations,
I would suggest visiting the UNFCCC CDM site (<a
href="http://cdm.unfccc.int/">here</a>), searching for (<a
href="http://cdm.unfccc.int/Projects/projsearch.html">here</a>)
and reviewing some of the submissions made.<br>
<br>
<br>
d.<br>
<div class="moz-signature">-- <br>
<div style="font:Georgia" ;=""><span style="font-size:110%;">David
William House<br>
</span>
<div style="padding-left:3em;font-size:80%;">"The Complete
Biogas Handbook" <code><a href="www.completebiogas.com">www.completebiogas.com</a></code><br>
<em>Vahid Biogas</em>, an alternative energy consultancy <code><a
href="www.vahidbiogas.com">www.vahidbiogas.com</a><br>
<br>
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<div style="padding-left:2em;">"Make no search for water.
But find thirst,<br>
And water from the very ground will burst."
<div style="padding-left:2em;font-size:80%;">(Rumi, a
Persian mystic poet, quoted in <em>Delight of Hearts</em>,
p. 77) <br>
<br>
<a class="moz-txt-link-freetext" href="http://bahai.us/">http://bahai.us/</a></div>
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