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Here is my third post. It was to be my last because the discussion suddenly 
went downhill after that.

I am one of those impressed by evidence of  human causes for global warming. 
But if I am to practice what I preach about objective scientific inquiry, I 
suppose I need to look seriously at the other side's science before I become 
too infatuated with my own perspective.

I take it as a fact that measurements have demonstrated a recent history of 
global warming. What is more controversial is whether it is a natural or 
human-caused trend.

The best scientific argument against human causation is the existence of a 
natural  warming trend starting with the end of the "Ice Age" 12,000 years 
ago and of natural climate fluctuations since then.  We appear to be 
involved in an upturn after a downward fluctuation called the "Little Ice 
Age"(LIA). The LIA was a relatively cool era during which glaciers and pack 
ice expanded.  The LIA was preceded by a relatively warm period called the 
"Medieval Warm Period" or the "Medieval Climate Optimum," which occurred 
roughly between 800 C.E. and 1300 C.E.  Experts disagree on when the LIA 
began and whether it was primarily a European, Northern Hemisphere or 
world-wide phenomenon. There seems to be little dispute, however, that the 
Little Ice Age ended c. 1850 C.E. See generally 
http://en.wikipedia.org/wiki/Little_Ice_Age (The web posting includes a nice 
temperature graph).

Note that the end of the LIA ended just as the Industrial Revolution and a 
large human population expansion began. Proponents of a human cause 
hypothesis of global warming track the coincidence between carbon emission 
and temperature increases and infer that the emissions caused the warming. 
Proponents of a natural cause explanation argue that the correlation between 
rising "greenhouse gas" levels and rising temperatures is either completely, 
or at least partly coincidental.

Proponents of the natural cause hypothesis are at a disadvantage vis a vis 
the human cause theorists because they have a smaller amount of data to work 
with. There is, however, at least some evidence to support two possible 
causes of global warming other than human activity -- i.e. decreased solar 
activity and/or increased volcanic activity. A third possible cause --  
changes in ocean currents -- is supported by even less data. But it deserves 
to be ruled out because ocean currents have such a large impact on climate.

If there is a purely natural explanation for global warming, science should 
be able to pinpoint it with further effort. If an explanation that goes 
beyond speculation about decreased solar activity and/or increased volcanic 
activity has already been discovered, I d like to know what it is.

One argument I don't want to hear goes like this, "It's too complicated. 
We'll never figure it out. Therefore, let's not even try. In the meantime 
why not keep on polluting the air?"  That argument is driven by politics, 
not science.

Bob Fisher
Independence, Missouri
[log in to unmask] 

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