[Lowfer] Global cooling or warming???

[Chris Trask]

>
> How does the Great Conveyor Belt fit into this?
>

    A significant input to the conveyor is the "chimneys" in the North
Atlantic, where less salty, colder water moving southward merges with
saltier, warmer water flowing northward in the surface layers.  When these
two water masses converge, they reach a point where the density of the water
(due to temperature and salinity) will cause it to flow vertically downward
in the form of "convective chimneys", where it then flows southward along
the ocean floor.  This phenomenon is known as the "Atlantic meridional
overturning circulation" (AMOC) and is a form of thermohaline circulation
(THC).  It's a forcing vector that keeps the conveyor flowing.

    There are two significant changes that have been taking place, the most
obvious one being the melting of the northern latitude ice.  This makes the
water moving southward less salty, which makes it flow more readily over the
warmer water moving northward.  At the same time, the water moving northward
is warmer, so as it passes through the subtropics and tropics there is more
evasporation, making the water saltier.  These two vectors were supposedly
going to cause the AMOC region to move southward, eventually causing the
climate in Britain and other areas to resemble Siberia, in a scenario known
as "Sudden Climate Change".  A similar event took place in the northern
hemisphere about 8,000 years ago when a large freshwater lake over northern
Canada suddenly emptied into the Arctic Ocean as the ice sheet was
retreating.

    However, there is another form of sudden climate change that is
appearing to be more likely.  In time, the amount of northern latitude ice
will diminish, and the southward flow of colder, lighter water into the AMOC
region will become warmer and saltier.  Additionally, with the polar ice cap
greatly reduced the Arctic Ocean water will become warmer by way of solar
absorption.  At the same time, the denser and warmer northward flow will
become increasingly warmer and saltier, and the result will be a rapid
northward shift of the AMOC region.  You can imagine what will happen then.

    Either way, what has been happening is that the number of these
convective chimneys has greatly diminished.  In the early 60s, there were as
many as 13 regions along the belt where this was taking place.  At last
count, there were two.  The British researcher Peter Wadhams has been
keeping track of these for decades:

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

    A book well worth reading is "The Two-Mile Time Machine" by Richard
Alley.  He's a strong proponent of the sudden cooling scenario, and among
other things he discusses the three known forms of solar forcing that have
100,000, 40,000, and 19,000 year cycles.

    An aspect of this trend that was interesting to watch this past summer
was a significant cooling of the surface of the Northern Pacific, generally
known as a "sea surface temperature anomally".  This has some odd effects to
the Eastern Pacific hurricane season, in particular the spectacular end of
hurricane Jimena.  A category 4 storm, Jimena was initially forecast to pass
into central Arizona and dump 4-8" of rain into the lower desert, which
would have been a disaster due to flooding.  Instead, it ran head-on into a
strong cold front which stopped it dead in its tracks and then ripped it
apart, in what one NHC forecaster called a "textbook case of shearing".  A
later category 5 storm met a similar but less spactacular end.  The colder
Northern Pacific provided the strong shearing winds that put the kabosh on
the Atlantic hurricane season.

    And if you think all this is interesting, just wait until this next
cutoff low sweeps deeply into northern Mexico and then along the Gulf Coast.
It's getting pretty wierd out there.

Chris Trask
N7ZWY
WDX3HLB
Senior Member IEEE
http://www.home.earthlink.net/~christrask/