[meteorite-list] Arrow head found in box of Moroccan Meteoritefragments.

[Darren Garrison]

On Sat, 9 Jun 2007 14:41:12 -0700 (PDT), you wrote:

>This post simply underlines a theory I had presented
>to me 10 years ago, that global warming is just a
>phase.
>If as little as 13000 years ago, the sahara was
>watered grassland, and the sahara grew before
>industry, how likely that we are the influence of
>climate change?

It isn't as clear cut as that.  First off, I'm not claiming to be an expert on
the Sahara desert, I'm just tossing ideas around.  But if there was a heating of
the Sahara 13k years ago, that'd be local warming (even though it is a fairly
big location) and wouldn't necessarily say anything about global temperatures.
Plus, desertification could mean not changes in temperature, but changes in rain
patterns-- 13k years ago, the Sahara could have been a 100 degree grassland that
became a 100 degree desert.  Humans could have cut down trees and burned off
ground cover, allowing soil to blow away and moisture to no longer be held in
the ground.  And once a desert starts, it tends to grow, with blown sand
covering bordering vegitation, killing it, slowly expanding it.  And you could
even theorize desert expansion with a COOLING atmosphere-- cooler air holds less
moisture and evaporates less from ocean/lake surfaces, so there is the
possibility of dryer areas in the world with a cooling trend (and the
theoretical possibility of global warming making some areas of the world greener
with increased rainfall).  So desert formation may or may not say something
important about overall warming trends, and it may or may not say something
about human causes.

Look at the US dust bowl, which, because of human farming practices, was pretty
darn close to desertification:

http://en.wikipedia.org/wiki/Dust_bowl