[Coral-List] NOAA Issues Unscheduled El Nino Advisory
riskmj at univmail.cis.mcmaster.ca
Sat Sep 16 09:15:51 EDT 2006
Hello Martin, Gene, colleagues.
The suggested explanation for the cooling seen in the oceans-that
increased sunlight has led to more evaporation, hence more cloud
cover-makes intuitive sense. But this is one of the many areas of which
I know naught.
The Nature article also makes reference to another chilling aspect,
that the ice caps seem to be melting faster than we had thought.
The idea that an ocean warming episode leads to a return of glacial
conditions in the Northern Hemisphere has been well-described, and I
will go over it a bit here because it's counterintuitive to think that
a warming leads to a cooling.
As far as I understand the oceanography (and I hasten to add here that
I do not understand it well), one major difference between glacial and
interglacial conditions is the abscence or presence of the Gulf Stream.
Without the Gulf Stream (often sanitised to the North Atlantic Drift),
NW Europe would be lots cooler. Stockholm is about the same latitude as
Nain, Labrador. I have been to both places. One is nicer. Without the
GS, there would be no wines in Bordeaux, and civilization would be very
different in Scandinavia.
In times past, large meltwater episodes have shut down/diverted the GS.
We are not sure exactly what happens-the fw lid may sit on it and drive
it deeper, or it may be diverted to the south. In any event, one such
meltwater disruption has been well documented: the Younger Dryas Event
was a brief (1,000 years) return to glacial conditions for much of
western Europe, about 11,000 years ago, caused by a diversion of the GS
by an enormous meltwater event.
As the icecaps on North America melted, the meltwater at first went
down the Mississippi. Then for a while meltwater went down the Hudson
River. All the while, an enormous lake, Lake Agassiz, was ponding over
Manitoba, behind the icesheets. This would have been larger than all
the Great Lakes combined.
At some critical moment, the St Lawrence Channel opened up, providing a
shortcut: Lake Agassiz drained in a few years. The fw pulse disrupted
the GS, giving rise to the glacial conditions in Europe. Note that this
happened on a globe that was warming: the cooling of Europe was only
the result of removal of the heat engine that supplies something like
1/3 its heat budget. Only.
There is ample evidence now that the GS is weakening, and so is the GS
Return Flow. Those who do not learn from history may shiver in the
dark: and it may all happen very quickly. I refer the energetic reader
to Nature, April 1997: Smith et al, "Rapid climate change..."
Smith (whom I am delighted to say is now Mrs. Risk) got hold of some
deep-water corals that grew in the GS Return Flow, during the onset of
the Younger Dryas. She was able to identify the event, and to show that
the onset occurred in less than 5 years.
As usual, there is no good news.
On Fri, 15 Sep 2006 13:26:46 -0700 (PDT)
Martin Moe <martin_moe at yahoo.com> wrote:
> Hi Gene, I recall reading a year or so ago about how
> global warming in the Atlantic might have an effect
> opposite of what one might expect and could even cause
> a minor "ice age" in Europe. The theory was that the
> warming melts the Greenland ice sheet (which is
> happening), and this cold water flows into the North
> Atlantic and disrupts, somehow, the deeper warmer
> "conveyer belt" currents that return water to replace
> the movement of surface currents, which might change
> the European climate to colder winters and short
> summers. If so, maybe what you refer to is a product
> of this phenomenon? Perhaps someone who knows what
> they're talking about could weigh in on this.
> --- Gene Shinn <eshinn at marine.usf.edu> wrote:
> > Mark, I am confused. El Nino is supposed to cause
> > ocean warming
> > while it winds stop hurricanes in their tracks yet a
> > lead news item
> > in NATURE, 24 August, titled "Oceans cool off in
> > hottest years"
> > says "the world's seas have cooled substantially
> > during some of the
> > warmest years in recent history. The data to be
> > published in
> > Geophysical Research Letters, based on measurements
> > from a global
> > array of 2500 floating sensors (ARGO program), show
> > the oceans have
> > cooled down to a depth of 750 meters over the past 2
> > years. Its all
> > very confusing, I can only imagine how it confuses
> > the public that
> > pays the bills. Gene
> > --
> > No Rocks, No Water, No Ecosystem (EAS)
> > ------------------------------------
> > -----------------------------------
> > E. A. Shinn, Courtesy Professor
> > University of South Florida
> > Marine Science Center (room 204)
> > 140 Seventh Avenue South
> > St. Petersburg, FL 33701
> > <eshinn at marine.usf.edu>
> > Tel 727 553-1158----------------------------------
> > -----------------------------------
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