suggestions for deciduous substitution?

Martin E. Lewitt lewitt at swcp.com
Sat Jan 13 07:47:48 EST 2001


In article <20010112212636.23663.00000943 at ng-fa1.aol.com>,
Iris Cohen <iriscohen at aol.com> wrote:
><< Recent research reports that North American evergreen
>forests rather than fighting global warming as carbon sinks
>may be contributing to global warming by absorbing more
>heat  in the winter because they are less reflective of 
>sunlight than the winter snow cover. >>

>Sounds like hogwash. Was this reported in a scientific peer reviewed journal?

I overstated. The authors word was that the albedo effect may
be "offsetting" some of the carbon sequestration.

I got my information from reading the
PHILIP BALL article  "Snow falling on cedars"
available free with registration at nature.com:

http://www.nature.com/nsu/001109/001109-10.html

Here is a quote from that article:

   At high latitudes, where snow covers the ground for part of the
   year, forests reduce the albedo. If snow falls on farmland or
   uncultivated scrubland, it can produce a uniform, bright covering.
   But snow falling on northern conifer forests tends to fall off the
   treetops, so that the dark forest canopy remains exposed.

   So forested land acquires a higher albedo when it is cleared for
   cultivation, at least in winter. Betts computer models of the worlds
   climate system show the effect of this.

Here are the first paragraphs (all that is free) of the actual
research articles the news feature story is based on.  I should
note that the feature story was supplemented by an interview with
the authors, so while their research was peer reviewed,  their
conclusions may be their own.   -- Martin

The Nov 9, 2000 issue of Nature had these two first paragraphs
available on the net for free:

Nature 408, 187 - 190 (2000) ) Macmillan Publishers Ltd.  

Offset of the potential carbon sink from boreal forestation by
decreases in surface albedo
RICHARD A. BETTS

Carbon uptake by forestation is one method proposed to reduce net
carbon dioxide emissions to the atmosphere and so limit the radiative
forcing of climate change. But the overall impact of forestation on
climate will also depend on other effects associated with the creation
of new forests. In particular, the albedo of a forested landscape is
generally lower than that of cultivated land, especially when snow is
lying, and decreasing albedo exerts a positive radiative forcing on
climate.  Here I simulate the radiative forcings associated with
changes in surface albedo as a result of forestation in temperate and
boreal forest areas, and translate these forcings into equivalent
changes in local carbon stock for comparison with estimated carbon
sequestration potentials. I suggest that in many boreal forest areas,
the positive forcing induced by decreases in albedo can offset the
negative forcing that is expected from carbon sequestration. Some
high-latitude forestation activities may therefore increase climate
change, rather than mitigating it as intended.

Nature 408, 184 - 187 (2000) ) Macmillan Publishers Ltd. 

Acceleration of global warming due to carbon-cycle feedbacks in a
coupled climate model
PETER M. COX, RICHARD A. BETTS, CHRIS D. JONES, STEVEN A. SPALL & IAN J. TOTTERDELL

The continued increase in the atmospheric concentration of carbon
dioxide due to anthropogenic emissions is predicted to lead to
significant changes in climate. About half of the current emissions are
being absorbed by the ocean and by land ecosystems, but this absorption
is sensitive to climate as well as to atmospheric carbon dioxide
concentrations, creating a feedback loop. General circulation models
have generally excluded the feedback between climate and the biosphere,
using static vegetation distributions and CO2 concentrations from
simple carbon-cycle models that do not include climate change. Here we
present results from a fully coupled, three-dimensional carbonclimate
model, indicating that carbon-cycle feedbacks could significantly
accelerate climate change over the twenty-first century.
We find that under a 'business as usual' scenario, the terrestrial
biosphere acts as an overall carbon sink until about 2050, but turns
into a source thereafter. By 2100, the ocean uptake rate of 5 Gt C yr-1
is balanced by the terrestrial carbon source, and atmospheric CO2
concentrations are 250 p.p.m.v. higher in our fully coupled simulation
than in uncoupled carbon models, resulting in a global-mean warming of
5.5 K, as compared to 4 K without the carbon-cycle feedback.
-- 
Personal, not work info:         Martin E. Lewitt             My opinions are
Domain: lewitt at swcp.com          P.O. Box 729                 my own, not my
Hm phone:  (505) 281-3248        Sandia Park, NM 87047-0729   employer's. 






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