Steve Schulin wrote:

Phil Hays wrote:

To talk about CO2 as
having a single "lifetime" is too simple of a model. This is why:

The exchange of carbon as CO2 with the mixed layer of the oceans has a
very short time scale, on the order of years. This process is
reversible by just reducing the CO2 level in the atmosphere.

The sequestration of carbon in silicate rock weathering has a longer
time scale, on the order of 100,000 years. This process is not
directly reversible, but is reversed by plate tectonics.

If we tried to measure the "lifetime" of CO2 over a few years, we
would see mostly the results of the first process. We would measure a
"lifetime" less than a decade.

If we tried to measure the "lifetime" of CO2 over a million years, we
would see mostly the results of the second process. We would measure
a "lifetime" on the order of 100,000 years.

With just these two processes, there would no single lifetime for CO2.
The "lifetime" we would measure would depend on how long of time
period we looked at. Of course, reality is more complex than this.
But that doesn't change the conclusion. There is no single lifetime
for CO2.

Gee whiz, Phil. I have repeatedly specified the timeframe I'm
discussing. It is the timeframe relevant to such questions as whether
anthropogenic emissions will result in doubled atmospheric
concentrations of CO2 in policy-relevant period.

Don't confuse reality with your interests. The assumption of a
single "lifetime" does not allow for measuring the real parameters of
the system. This has nothing to do with the use of estimates of these
parameters for policy.


--
Phil Hays