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Re: Human vs. natural influences on the environment



charliew@hal-pc.org (charliew) wrote:
>I made no assumptions in my statements.

They were implied by the language, but not stated.

>  I was trying to 
>point out that a long time constant by itself is not 
>necessarily detrimental.

If you apply a delta function to a second or higher order
system with a long time constant, it will continue reacting
to the input for a considerable time after it has been
removed.  Presence of a long time constant is not
necessarily beneficial or even neutral either.

>  Whether a system as large as the 
>atmosphere can be substantially affected over a 1 year time 
>interval is open to debate, and something that I consider to 
>be merely a matter of your opinion.

Do you consider the winter/summer atmospheric temperature
differential in Montana to be a matter of my opinion?  How
about over the entire northern hemisphere?

I personally try to keep an open mind, but not so far open
that my brain falls out.  Apparently some are not so careful.

>  However, even if I 
>assume that this is true, a time constant this short implies 
>that we can also move the atmosphere an equal amount in the 
>opposite direction in the same 1 year period.  So, where's 
>the problem here?

First, the forcing function is not a delta.  It is closer to
a ramp or an exponential curve.

Second, how could the concentration of CO2 in the atmosphere
be reduced quickly in a short period of time to move the
atmosphere in the other direction?  You gloss over the lack
of means to accomplish this end.

Third, the time constant of the atmosphere is not the only
matter of concern.  There is also the heat capacity of the
oceans and the influence of ocean circulation on climate.
The time constant of the oceans is measured in years, and
if a change in buoyancy from oceanic heating should cause a
change in ocean currents, the result could be enormously
greater than a fraction of a degree C in average temperature.
There is also no guarantee that restoring the temperatures
would return the circulation to its previous pattern.

Perhaps we can understand these things with good enough
models and lots of study, and determine what we can and cannot
do safely.  Right now we don't know, so it behooves us to
tread very carefully.

I should note here that a Chernobyl disaster every decade
would not have the devastating impact on Europe that a shift
in the circulation of the Gulf stream would have.



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