date: Fri, 20 Feb 2004 13:58:03 -0000
from: "Emma L. Tompkins" <e.tompkins@uea.ac.uk>
subject: FW: Re: Abrupt Climate Change
to: <tyn.building@uea.ac.uk>

FYI 2
-----Original Message-----
From: John Shepherd [mailto:j.g.shepherd@soc.soton.ac.uk] 
Sent: 20 February 2004 09:59
To: Alex Jackson; Gareth Morgan; Claire Powell; Stephen Powell; Lindsey
Stones; Ben Ward; Maxwell Gonzales; Mathieu Theron; Helen Luke; Rachel
Hadfield; Adam Williams
Cc: tyndall-soton@soc.soton.ac.uk
Subject: Fwd: Re: Abrupt Climate Change

... and also this...

>X-Sender: koutavas@hesiod
>Date: Thu, 12 Feb 2004 15:52:15 -0500
>To: Andy Revkin <anrevk@nytimes.com>
>From: Athanasios Koutavas <koutavas@mit.edu>
>Subject: Re: finally preparing to write an update on prospects for
>  abruptness
>Cc: Mark  Cane <mcane@ldeo.columbia.edu>,
changelings@ldeo.columbia.edu,
>         lea@geol.ucsb.edu, Sandy.Tudhope@glg.ed.ac.uk, 
> rich@ldeo.columbia.edu,
>         peter@ldeo.columbia.edu, jchiang@atmos.berkeley.edu
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>
>Dear Andy,
>
>I have some thoughts for you.
>
>Even in the (unlikely) absence of a human impact on climate we would
still 
>need to worry about natural abrupt climate change.  It's true that by 
>comparison with the glacial world, the interglacial climate has been
less 
>"angry". But it has not been stable and it has not varied smoothly, and
it 
>can certainly wreak havoc in regions strained by overpopulation or by 
>scarce food and water resources, typically found in the tropics and
subtropics.
>
>If one looks at the Cariaco Basin sediments offshore Venezuela (the 
>tropical climate archive "par excellence") one sees that dramatic and 
>abrupt hydrologic changes occurred over the last 4,000 years, and they 
>appear to be linked to instability in the position and/or intensity of
the 
>ITCZ. Some of these (in fact the more modest ones) were large enough to

>disrupt the Mayans or perhaps do them in. If Cariaco is any indication
we 
>are currently in a phase of active century-scale (probably decadal
scale 
>as well, but here one needs very finely resolved data) variability in 
>tropical rainfall patterns which are governed largely by the ITCZ.
>
>This brings me to the eastern Pacific, which you will note is very
close 
>to Cariaco. I would maintain that it is impossible to have the kind of 
>ITCZ-related variability observed in Cariaco without affecting the ENSO

>system in the Pacific. This is because the equatorial cold tongue in
the 
>Pacific (the most sensitive ENSO element) is coupled to the ITCZ. As
the 
>ITCZ is displaced northward, conditions are more favorable for La Nina
and 
>vice versa.
>
>In fact, there is strong evidence that the Cariaco ITCZ archive and 
>records of Holocene ENSO are linked: Cariaco suggests the ITCZ was
further 
>north in the early-middle Holocene; we have evidence from Papua-New
Guinea 
>corals and sediments from Lake Pallcacocha, Ecuador, that El Nino was
weak 
>at that time. We also have evidence that cold tongue temperatures were 
>cooler. All of this suggests a persistent La Nina bias. We believe
modern 
>ENSO really became established after ~5,000 ago, and this occurred as
the 
>ITCZ shifted southward. ENSO and the ITCZ have been clearly linked
during 
>the Holocene.
>
>Perhaps most importantly, Cariaco suggests the ITCZ has been moving
north 
>since the Little Ice Age, and this is reflected on the Pacific side in 
>corals from Galapagos and Panama. This northward shift may not have 
>crossed a threshold yet to affect ENSO, but if it continues it may well

>lead us into a mid-Holocene climate analog with a strong La Nina bias
in 
>the Pacific. To echo Richard Seager, this could have serious
consequences 
>for water resources in North America, to say the least.  (By the way
you 
>don't have to go back to the Dust Bowl to get a sense of this. The mild

>4-year La Nina conditions following the 1998 El Nino, caused widespread

>water shortages and drought in the US and Southern Europe). Could this
be 
>facilitated or accelerated by anthropogenic warming? I would argue yes,
if 
>the warming favors the Northern Hemisphere which would promote a more 
>northerly ITCZ. Given the observed warming in the Arctic and the
potential 
>for sea-ice albedo feedback, as well as the larger land surface area in

>the Northern Hemisphere, this seems well within the realm of
possibility.
>
>While I am convinced that the THC switch is operative and is a big part
of 
>the glacial climate instability, I have reservations that it played a 
>prominent role during the Holocene. With the possible exception of the
8.2 
>ky event which probably had a glacial meltwater trigger, the evidence
for 
>THC instability in the Holocene is weak. (Can anyone point me to the 
>strongest evidence?) Contrast this with the evidence for ENSO
variability, 
>which incomplete as it is, is staggering. We have gone from a nearly 
>absent El Nino regime ~7,000 years ago to the large El Nino events of
the 
>late 20th century. Granted, the long-term modulation of this was likely

>due to the precession cycle, but there have been many abrupt bumps on
the 
>way, whether you look at Lake Pallcacocha or the Cariaco records.
Simply 
>put, the Holocene displays the largest range of ENSO conditions
observed 
>in the geologic record, period.
>
>For this reason I think we are more likely to see the first signs of 
>abrupt climate change in the tropical ocean-atmosphere system, that is,
in 
>tropical SST and rainfall anomalies. Particularly so in the Pacific
where 
>the coupled cold tongue-ITCZ system is just as fast-acting a climate 
>switch as any. Naturally, should this occur we can expect to see global

>effects, not excluding the THC.
>
>Would be glad to provide references if needed.
>
>Cheers,
>Tom
>
>
>>HI all,
>>
>>Very belated, and prompted in part by what seems an overly hyped
Fortune 
>>magazine article on evidence for near-term abrupt change driven by 
>>warming, i'm actually going to commit journalism soon on the subject.
>>
>>What I'd like to do is clarify what is known, unknown and perhaps 
>>unknowable as we look at the past (younger dryas etc), and ahead (fram

>>strait trends etc). My sense is that Wally B's notion that the 'angry 
>>beast' is a creature of colder eras but not of warmer times has some 
>>support. I'd like to get more familiar with the data and/or theory
that 
>>supports that.
>>
>>Also, separately, been intrigued by Richard Seager's analysis of 
>>importance of air flows instead of ocean flows in modulating European 
>>climate. Is that relevant to the abruptness question?
>>This is also prompted by my focus on Arctic recently.
>>
>>Any trenchant thoughts about these matters appreciated.
>>could start with simple statement from you giving your feeling about 
>>whether evidence is building supporting the prospect for a
warmer-world 
>>angry beast or whether it is eroding?
>>
>>You can pop a few paragraphs as a conversation starter or we can
arrange 
>>a time to talk a bit.
>>
>>Thanks again!
>>
>>andy
>>_____________________________________
>>Andrew C. Revkin
>>Environment Reporter
>>The New York Times
>>229 West 43d St. NY, NY 10036
>>
>>Tel:   212-556-7326
>>Fax:  509-357-0965 (via www.efax.com, received as email)
>
>
>--
>--------------------------------------
>Athanasios Koutavas, Ph.D.
>NOAA Postdoctoral Fellow on Climate and Global Change
>Dept. of Earth, Atmospheric and Planetary Sciences
>Massachusetts Institute of Technology
>77 Massachusetts Avenue, E34-172
>Cambridge, MA 02139-4307
>USA
>
>Phone: 617-324-0282
>Fax: 617-253-8630
>Email: koutavas@mit.edu
>--------------------------------------



