Re: [Paddlewise] Global warming

From: "SRI" <sailboatrestorations_at_worldnet.att.net>
> 
> Anyway, the subject of global warming is of great interest to me.  I have
> been trying to learn more about it, but I find information hard to get.
> Lots of the sources seem to be "fringe" groups with too much rhetoric and
> not enough straight factual info.  Anyone know how one might really learn
> about this subject?  TIA.
> 
> Mark

Go to this site and do a search on " global warming "

http://scienceweek.com/swfr.htm

Also, the following is from this week's Scienceweek issue, retransmitted 
with permission (a side note, PaddleWise discussions include issues of 
environmental concern which can affect our marine environment):

from Science Week, 11 August:

1. EARTH SCIENCES:
CAUSES OF CLIMATE CHANGE OVER THE PAST 1000 YEARS
     The physical basis of the so-called "greenhouse effect" is
essentially as follows: Carbon dioxide gas is transparent to
visible light but relatively opaque to infrared radiation. The
same is true of glass. Relatively high-energy visible light
radiation from the sun passes inward through the atmosphere,
warms the surface of the Earth, which then radiates lower energy
in the form of infrared radiation (heat) back to the atmosphere.
But if the atmosphere has a concentration of infrared
impenetrable gases such as carbon dioxide, the infrared radiation
cannot pass out, and the surface of the Earth underlying the
atmosphere cannot cool, and the surface of the Earth thus will
continue to grow hotter.  
     There is no significant disagreement concerning the
mechanism of the greenhouse effect, but the consequences of the
effect, particularly for future global climate, are unclear.
... ... Thomas J. Crowley (Texas A & M University, US) presents a
detailed study of the causes of climate change over the past 1000
years, the author making the following points:
     1) The author points out that the origin of the late-20th
century increase in global temperatures has prompted considerable
discussion. Detailed comparisons of climate-model results with
observations suggest that anthropogenic changes, particularly
greenhouse gas increases, are probably responsible for this
climate change. There are, however, a number of persistent
questions concerning these conclusions that involve uncertainties
in the level of low-frequency unforced variability in the climate
system, and whether factors such as an increase in *solar
irradiance or a reduction in *volcanism might account for a
substantial amount of the observed 20th century warming. Although
many studies have addressed these issues from the paleoclimate
perspective of the past few centuries, robust conclusions have
been hampered by inadequate lengths of the time series evaluated.
     2) The author reports that the agreement between model
results and observations for the past 1000 years is sufficiently
compelling to allow one to conclude that natural variability
plays only a subsidiary role in the 20th century warming, and
that the most parsimonious explanation for most of the warming is
that it is due to the anthropogenic increase in greenhouse gases.
     3) The data used in this study included physically based
reconstruction of Northern Hemisphere temperatures and indices of
volcanism, solar variability, and changes in greenhouse gases and
*tropospheric aerosols.
     4) The author concludes: "There are... two independent lines
of evidence pointing to the unusual nature of late-20th century
temperatures. First, the warming over the past century is
unprecedented in the past 1000 years. Second, the same climate
model that can successfully explain much of the variability in
Northern Hemisphere temperature over the interval 1000-1850
indicates that only about 25% of the 20th-century temperature
increase can be attributed to natural variability. The bulk of
the 20th-century warming is consistent with that predicted from
greenhouse gas increases. These two lines of evidence provide
further support for the idea that the greenhouse effect is
already here."
-----------
Thomas J. Crowley: Causes of climate change over the past 1000
years.
(Science 14 Jul 00 289:270)
QY: Thomas J. Crowley [tcrowley_at_ocean.tamu.edu]
-----------
Text Notes:
... ... *solar irradiance: In general, the amount of solar
irradiation received from the Sun.
... ... *volcanism: In general, the eruption of lava.
... ... *tropospheric aerosols: The term "troposphere" refers to
the lowest 10 to 20 kilometers of the atmosphere (with the lower
boundary the surface of the Earth). The term "aerosol" refers to
a dispersion in which a finely divided solid is suspended in air
and the particles are of colloidal dimensions. The term
"colloidal dimensions" refers to the range approximately 1
nanometer to 100 nanometers in diameter.
-------------------
Summary & Notes by SCIENCE-WEEK http://scienceweek.com 11Aug00
For more information: http://scienceweek.com/swfr.htm

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