----- Original Message -----
From: "Michael Tobis" <[EMAIL PROTECTED]>
Newsgroups: gmane.science.general.global-change
To: <[email protected]>
Sent: Wednesday, July 04, 2007 12:27 PM
Subject: [Global Change: 1857] Re: breaking the population bomb taboo
>
> I have a relatively minor point, in the present context, about forests
> and carbon balance, but I feel compelled to make it. I also address
> some of the larger issues below.
>
> On 7/4/07, Don Libby <[EMAIL PROTECTED]> wrote:
>
> ...
>> As evidence of overpopulation, Rapley cites a
>> World Wildlife Fund figure of "1.25 earths needed to sustain the
>> population", which is down from 5 earths just a few short years ago.
>
> While I don't know what goes into the calculation (and would like to
> know), your analysis about forests is incorrect.
Not my analysis. My reading of University of British Columbia urban
planners Reese and Wackernagel who first published the "ecological
footprint" concept (a rehash of ancient carrying capacity thought for modern
mass consumption.) I'm sure you can google your way to the source but five
or ten years ago I went through their article fairly carefully and traced
the adoption and diffusion by others such as the World Economic Forum and
WWF. Acreage for trees to absorb carbon is the biggest part of the
footprint, and as you point out, among the more dubious. But the larger
point is that the whole enterprise of carrying capacity measurement is
dubious.
>
> Nevertheless, the question of what the maximum population that can be
> sustained indefinitely actually is remains a real one. We may not know
> how to do something and still need to do it.
Like studying perpetual motion? Grant funding is pretty thin in that field,
for good reason.
Michael, that question is not a real one, it is a hypothetical conjecture at
best. The authoritative encyclopedia of carrying capacity estimation is
geographer Joel Cohen's 1995 _How Many People can Earth Support?_ It will
satisfy your curiosity about quantification efforts, but the estimates range
to a high of 10^12 - maximum indefinitely sustainable population (with
people stuffed into huge nuclear powered anthills spaced evenly over earth's
land and ocean surface).
As you will find in the "consensus statement" cited previously, the *real*
questions are what kind of life we want to live, what kind of environmental
quality we want to preserve, and so on - these are questions of human
values, not of scientific laws that constrain human activity. Human
activities are constrained by scientific laws, but "global population
carrying capacity" is not one of them. The possibility is not excluded by
the laws of physics or biology.
>
>> The global population is currently stabilizing, carbon emissions are not.
>
> I still think it is worth considering what the goal should be.
> Regardless of the actual number, in the very long run the only
> sustainable global fertility is the one that exactly balances
> mortality (and in the unlikely event that space travel ever becomes
> important in this matter, net emigration)
Michael, in the very long run we are all extinct - species only last an
average of 4 million years. Fertility and mortality rates can fluctuate
over time, and in the limit as t goes to infinity, the average is zero.
Natural preadator-prey cycles may oscillate sinusoidally with birth and
death rates locked in phase but rarely equal - such cycles may be
sustainable without "exact balance". Biologist Stewart Pimm has shifted
thinking about population equilibrium away from the rigid notion of carrying
capacity and toward a much more dynamic concept of "resilience" with
populations and resources swinging about through more-or-less broad ranges
of tolerance.
As I've said before, in my opinion the goal should be "stabilization".
Under current conditions, we're well on the way to achieving population
stabilization by mid-century. We're doing less well on the carbon
stabilization front. Perhaps an accelerated decline in fertility would
increase the chances of carbon stabilization - I would agree that continuing
to promote the conditions associated with fertility decline is a laudable
goal for many reasons.
>
>> Therefore we must look to other causes of carbon emissions to deal with
>> them
>> effectively.
>
> I agree that this is far the more urgent problem. However, I would
> like to see the sustainability issue addressed quantitatively.
Yes the topic has fascinated many over the centuries (nod to Malthus - see
Cohen to more than satisfy your curiosity.) Today it is regarded as a
sterile concept, as one reviewer of Cohen put it "to be consigned to the
intellectual dead letter box" (F. Landis MacKellar review of Cohen in
_Population and Development Review_ March 1996 p 145).
>
> I am very puzzled about the tight correlation between income and
> fertility. We may be relying on it too heavily if we don't understand
> it. At my current level of understanding it strikes me as possible
> that cause and effect have been reversed. If so, it reminds me of my
> plan to plant palm trees in Wisconsin to make the winters less harsh.
>
> Don, or somebody, please reassure me that the causality is understood
> if you can.
>
> mt
>
Michael, the "cause and effect" is manifold and not strictly material, but
socio-cultural, summed up in the term "women's emancipation".
Here's my reassurance: relax good fellow. Relax with a good book reviewing
the research literature in an readable discourse: R.A. Easterlin _Growth
Triumphant: the 21st Century in Historical Perspective_ U Mich Press, 1997.
Also on your summer reading list: Brian O Neill, F. Landis MacKellar and
Wolfgang Lutz, _Population and Climate Change_. Cambridge University Press,
Cambridge, 2001.
Thanks for your thoughts,
-dl
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