From: userDHAL@mts.ucs.UAlberta.CA (David Halliwell)
Subject: Re: Lawyer's science vs. unbiased presentation of the facts
Organization: University Of Alberta, Edmonton Canada
Date: Thu, 30 Jul 1992 20:10:49 GMT

szabo@techbook.com (Nick Szabo) writes:

>In article <dhalliwe.712449793@muskwa.ucs.ualberta.ca> userDHAL@mts.ucs.UAlberta.CA (David Halliwell) writes:
> 
>>>Ecosystem impacts are caused by local, not global temperatures.
>>
>>    The only thing that short term variations are relevant to is the
>>subject of short term changes. Global warming is not a short term change
>>and thus the impact of short term changes is not relevant.

>You are making an artificial dichotomy between changes over a few
>years (which you miscall "weather") and changes over decades ("climate").
>After the temperature has changed, the ecosystem does not "wait" over 
>some long period to change; the organisms in question die or thrive 
>from the current, local temperatures and rainfall.  If there is an
>unprecedented biting spring frost, the leaves fall off that spring,
>not decades later.  If the species can survive at lower populations or 
>go dormant longer than a year, it can often last long enough to allow 
>migration.  

    No way, Nick. If the species can survive a period of dormancy of
one year, this is no guarantee that it can survive a dormancy of
one hundred years. New individuals require "good" years to germinate,
and then must grow enough to be able to withstand "bad" years. If the
bad years are too frequent, then none of the young plants will survive
to maturity. Other plants that *can* survive in the new climate will
have a competitive advantage, and will replace the old species over time.
We do not see major changes in plant communities over a period of one
or two years because individual plants often survive longer than this
and succession cannot occur over such a short time.
  
   The time period is critical: it is 2C warmer here in Edmonton now
than it was an hour ago. This warming has the same magnitude as
volcanic activity and CO2(predicted), and has occurred at a much greater
rate. However, plant response to this recent warming is of no use
whatsoever in looking at global warming.

   The biting spring frost is survivable only if it doesn't happen too
frequently. Look at weeds on your front lawn: they'll survive having
the leafs ripped off once (or twice), but if you go out and pull the
leaves off every day the weeds *will* die as they deplete their food
reserves trying to produce new leafs that never get a chance to
photosynthesize and replenish the reserves.
 
   Sure, the leaves fall off immediately following the frost. However,
that doesn't mean that a new frost-resistant species will migrate into
an area over the next week or two. This won't even happen over a year
or two. Probably not even over a decade or two. In order to favour
the growth of a different species, we would have to have recurring
late spring frosts, slowly discouraging the growth of the existing
species while allowing the establishment of a competitor.

   You are confusing the response of a single individual plant (or
a collection of individuals all living at the same time) with the
response of a plant community or an ecosystem.
 
   I referred to the volcanic and El Nino effects as weatherISH. They
are certainly *not* of sufficient duration to be called changes in
climate. They are simply part of the variability within the current
climate. They are of short enough duration that they only represent
a small portion of the conditions under which the plant community will
develop or survive.

>You also lump in Younger Dryas as such a short-term change, but 
>in fact the 7C change took 40 years and the new levels lasted for
>centuries.  Many volcanoes over the period of human evolution have 
>had impacts up to a decade long, with rate of change and magnitude greater 
>than the hypothesized global warming.  It's absurd to reject comparisons 
>to global warming because these are "weather" and global warming is
>"climate".  It is also premature to reject ENSO, Pinatubo, etc. as
>irrelevant to the issue of ecosystem change from global warming.  
>We can learn quite a bit from studying the changes induced by these
>shorter-term phenomenon.

    I have not lumped the Younger Dryas in with anything. I have not
referred to it at all in any of my posts. All of my comments have
been directed at volcanic and El Nino events.

   Volcanic effects tend to peak at most a year after the eruption.
After this time, the effects are decreasing in magnitude. The effect
is quite non-linear, so that even if the effect is still detectable
after 10 years, *most* of the effect has disappeared after just two
or three years. It is still a transient effect, rather than a permanent
one. The big difference between these and the Younger Dryas is in
your statement "lasted for centuries". This makes the Younger Dryas
of sufficient duration to be classified as climate change. It is the
only one of your examples that *is* relevant.


Dave Halliwell
Department of Geography
University of Alberta
Edmonton, Alberta
Newsgroups: sci.environment