cc: Nick McCave <mccave@esc.cam.ac.uk>, Bob Marsh <rma@soc.soton.ac.uk>, John Lawton <HQPO@wpo.nerc.ac.uk>
date: Tue, 10 Dec 2002 10:10:10 +0000
from: Jochem Marotzke <Jochem.Marotzke@soc.soton.ac.uk>
subject: RS Mtg., Abrupt Climate Change
to: Bob Dickson <r.r.dickson@cefas.co.uk>, Alan Kemp <aesk@soc.soton.ac.uk>, Richard Wood <rwood@meto.gov.uk>, Richard Alley <ralley@essc.psu.edu>, Eli Tziperman <eli@beach.weizmann.ac.il>, Harry Elderfield <he101@esc.cam.ac.uk>, Meric Srokosz <mas@soc.soton.ac.uk>, Brian Hoskins <b.j.hoskins@reading.ac.uk>, Andrey Ganopolski <andrey@pik-potsdam.de>, Hugh Jenkyns <hugh.jenkyns@earth.ox.ac.uk>, Mike Hulme <m.hulme@uea.ac.uk>, Christian Koerner <ch.koerner@unibas.ch>, Charles Perrings <cap8@york.ac.uk>

Dear All:

	Thank you again for agreeing to speak at our Royal
Society Discussion Meeting on 4/5 February next year. With
some of you perhaps having started to think about your
presentation and accompanying paper, I thought a few 
general thoughts about the science of Abrupt Climate Change
might be helpful in the discussion.

	Invariably, the question arises what is meant by
"Abrupt" in this context, and the committee, chaired by
Richard Alley, that wrote the "Abrupt Climate Change: 
Inevitable Surprises" report for the U.S. National 
Research Council struggled with this more than with any
other issue during the writing of the report. The difficulty
was, should we even try to define it? Or is all we can say
that we recognise it when we see it?

	In the end, we did tackle the "definition thing", 
and produced what I still feel is a good answer. In a 
paper that Richard was invited to submit to Science, we
summarised it as:

"Technically, an abrupt climate change occurs when the climate 
system is forced to cross some threshold, triggering a 
transition to a new state at a rate determined by the climate 
system itself and faster than the cause" (NRC, 2002, p. 14). 
The cause may be chaotic and thus undetectably small. For 
human concerns, attention is especially focused on persistent 
changes that affect subcontinental or larger regions, and for 
which ecosystems and economies are unprepared or are incapable 
of adapting. 

NRC, 2002. Abrupt Climate Change: Inevitable Surprises. 
National Academy Press,  230pp. See online version, 
http://www.nap.edu/catalog/10136.html
for the more comprehensive definition.

	I don't wish to be prescriptive, but you may find
this definition useful as a common reference point for our
discussion. 

Best regards,
Jochem Marotzke

-- 
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Professor Jochem Marotzke,       Jochem.Marotzke@soc.soton.ac.uk 
School of Ocean and Earth Science,    SOC, Room 566/11
University of Southampton,            Tel: + 44-(0)23-80593755 
Southampton Oceanography Centre,      Fax: + 44-(0)23-80593059
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Southampton SO14 3ZH, United Kingdom 
http://www.soes.soton.ac.uk/research/groups/ocean_climate
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