"Don Foreman" wrote in message
...
On Sun, 25 Jul 2010 22:14:45 -0400, "Ed Huntress"
wrote:


"Martin H. Eastburn" wrote in message
...
CO2 is CO2 no matter where it comes from.

From bugs man, forest fire, Oil Field on fire or decaying matter.

Martin

If it comes from recent photosynthesis, it adds nothing to the atmosphere.
If it comes from fossil fuels, it restores CO2 to the atmosphere that
hasn't
been there for millions of years. It increases CO2 levels as a result.

I think you mean "if it comes from oxidation of organic matter that
was produced by photosynthesis..." Photosynthesis doesn't release
CO2, it consumes it.

No, I meant that if the source of the sequestered CO2 is the result of
recent photosynthesis, then it adds nothing to the atmosphere that wasn't
there days, years, or a few decades ago. If its source was photosynthesis
that occurred millions of years ago, as in the oil example, then it adds to
current atmospheric CO2, by re-releasing carbon that was sequestered from
the atmosphere millions of years ago.


Any release of CO2 from any source adds immediately to the local
atmosphere.

But if the source is from recent plant life, it only adds back what was in
the atmosphere hours, or days, or perhaps a few decades ago, and had been
sequestered in the short term. And since the cycle is continuous, it adds no
net CO2 over time.

If that were not true then submarines wouldn't need CO2
scrubbers to deal with CO2 from respiration: just add oxygen to
replace that used.

That CO2 comes from stored food that they brought on board. If they didn't
eat food that was produced from plant life that recently sequestered CO2,
they wouldn't need CO2 scrubbers. They'd all be dead from starvation. d8-)


Simultaneously, current photosynthesis and other processes subtract
immediately from atmosphere in their locale. Any concentration
gradients that result are soon resolved by mixing due to winds and
Dalton's law of partial pressures. If these two processes balance
over a given period of time then there is no net change during that
period.

And that's EXACTLY what MUST happen with food, and human respiration. You
can only exhale CO2 that you breathed in, plus CO2 that's released from
metabolizing food. And the amount of carbon sequestered in that food can be
no less than the amount you exhale.

If the CO2 added by burning fossil fuel is not balanced by
a corresponding increase in subtraction by photosynthesis or other
subtractive mechanism, then atmospheric concentration will increase
over time. In fact, over the past 200 years or so we have both
increased the rate of addition and reduced the rate of subtraction by
destruction of vegetation.

Yup. It sounds like we're getting close to the underlying point about what I
said to Larry in the first place.


To mitigate this, we must look at both reducing production rate and
increasing subtraction rate. Breathing less is not a viable option
(pun intended) but fossil fuels are by no means the only other source
and subtraction is just as important in balancing the CO2 budget.

The CO2 budget for food and human respiration is directly related to the
sequestration of CO2 by plants that we eat. We can't exhale more than the
amount of CO2 sequestered in our food. And the amount of CO2 we breathe out
must be re-sequestered by the plants that form the basis of our food before
we can eat again -- like tomorrow. g

That's one of the clearest, least equivocal of the carbon cycles we deal
with. It's self-contained in the sense that we know how much carbon must go
in, and how much comes out, and we know the average time for that cycle to
complete itself. Other carbon cycles within the overall system dynamic
neither increase nor decrease the quantity of the carbon in the food cycle,
nor the cycle's velocity.

There are many other carbon cycles, such as the natural growth and decay of
forests. You can try to isolate them and get a handle on their individual
effects, or you can mix them all together indiscriminately and confuse the
hell out of anyone who's trying to understand it. g Certain cycles can be
treated exactly if they were closed; no matter where each molecule of CO2
came from, a specific amount must be sequestered in plants or we don't eat.
And that particular cycle is so isolated from things like burning fossil
fuels that it's often called a "carbon-neutral" cycle. Over the relevant
span of time (a few years), that's accurate to a high degree.

Burning fossil fuels is the exact opposite. That cycle is so long, and the
velocity of release is so extremely short in relation to the overall cycle
time, that it has large atmospheric effects.

We're not likely ever to go through the whole fossil-fuel cycle. It looks
like it's sequester once, re-emit the products once, and then it's all over.
After that, we're more likely to synthesize the products we used to get from
it -- something like what happened to whale oil. d8-)

--
Ed Huntress