"Scott Whitehead" wrote in message
om...
With ice sheets evidently on the move in the Arctic and Antarctic - in
terms of moving from one area to another - it occured to me on the way
into work today that surely deserts must do the same and there must be
accounts from subsistence farmers in the central African basin with
accounts that...
"The Sahara desert used to start here - now this area is well
irrigated and is being reclaimed by the savannah / jungle - the desert
is now three miles further north..."


Snip ...

There is no doubt that the anonymous Christian writer is correct when
he states that;
"Historical climate research indicates that climate change does not
follow a pattern that people seem to expect (the climate always
gradually and slowly changing over the course of a long time). Rather,
the evidence indicates that the planet can suddenly flip from one
climatic condition to a new equilibrium in about ten years.

The transactions of a meeting held at the Royal Society to discuss this
matter have just been published. See;
http://www.catchword.com/rsl/1364503...0/contp1-1.htm

The meeting was organised by oceanographers, hence the emphasis
on switching of ocean currents as the cause of these rapid changes.
However, papers by Wood, and by Gildor & Tziperman both point
to the trigger being sudden ice sheet changes altering the global
albedo which in turn is then amplified by the greenhouse effect of
water vapour. The contraction of the Arctic ice sheet, which has been
dramatic during the last two summers, could well trigger yet another
rapid change.

Without the Arctic sea ice present during the summer, that region
will warm, leading to more evaporation, water vapour, and greenhouse
warming from the increased water vapour which will have a positive
feedback effect. The warmth from the Arctic will spread south, as
it has done this summer, and will cause global temperatures to rise.
This will lead to more water vapour globally and a global temperature
rise leading to an abrupt climate change. Temperatures will rise until
the climate regime settles into a new state where the cloud cover has
increased such that its new albedo equals the loss in albedo from the
lost Arctic ice, and the global heat balance is restored.

What this new climatic regime will be like is anyone's guess, but it
probably will entail widening of the tropical zone with the sub tropical
deserts moving towards the poles. This summer has seen fires
on the northern coast of the Mediterranean and in north America.
These could have been made possible by drier regimes in those
regions caused by the subtropical deserts stretching their influence
northwards.

The writer of the article you quote says;
... In fact, given the increasing
tempo of change taking place on the Sahara (the signal environment)
we are actually coming up to the end of this ten year period, and in the
immediate future the climate will become stable in new equilibrium."

If I am correct we are not at the end of one of those phases. We are at
the beginning. Climatic disasters will continue to occur each year until
the Arctic ice has gone completely and the climate has settled into a
new patern of clouds.

HTH,

Cheers, Alastair.