date: Fri, 20 Feb 2004 13:58:03 -0000 from: "Emma L. Tompkins" subject: FW: Re: Abrupt Climate Change to: 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 >From: Athanasios Koutavas >Subject: Re: finally preparing to write an update on prospects for > abruptness >Cc: Mark Cane , 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 >X-Filter-Version: 1.7 (lamont.ldeo.columbia.edu) >X-MailScanner-SOC: Found to be clean >X-MailScanner-SOC-SpamCheck: not spam, SpamAssassin (score=-4.799, > required 5, BAYES_00 -4.90, RCVD_IN_NJABL 0.10, > RCVD_IN_NJABL_RELAY 0.00) > >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 >--------------------------------------