Talk:Holocene climatic optimum

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Contents 1 Temp range 2 Vostok plot 3 Page move? 4 New pic: new text? 5 Causes?

[edit] Temp range

(William M. Connolley 19:39, 4 Mar 2005 (UTC)) +4 oC didn't very likely to me. The Vostok core [1] shows nothing like that. RealClimate [2] (google hit #3 for "HCO temperature") says the term is outdated and the warmth is mostly NH summer. Google hit #4 http://www.iitap.iastate.edu/gccourse/history/paleoclimate/paleo_lecture.html shows us fig 1 (its IPCC '90 fig 7.1, which has no source) with approx +1 oC, but this is schematic only. The IPCC TAR doesn't show it much either http://www.grida.no/climate/ipcc_tar/wg1/073.htm. But I'm not an expert on this (perhaps DF is?... I'll ask).

I revised the article based on my understanding of the issue, including the restoring the +4 °C within its proper context. However, I am not entirely current on this issue so there may be additional changes needed based on recent research, such as you are citing. Dragons flight 21:42, Mar 4, 2005 (UTC)

(William M. Connolley 22:10, 4 Mar 2005 (UTC)) OK. I like your edit comment... I may try to find the GRIP/GISP data.

Which is the "recent research" he is citing? The RealClimate article, with climate simulation studies? Is that the source of all the boreal qualifications? Anything based on the real world? http://www.spacedaily.com/news/pacific-02c.html http://www.eurekalert.org/pub_releases/2004-12/osu-mcc121304.php (SEWilco 08:26, 5 Mar 2005 (UTC))

(William M. Connolley 10:42, 5 Mar 2005 (UTC)) The RC piece contains references, to actual papers, unlike your first version, or indeed your two links above.

My version of the article is based on a personal understanding of the issue that could very well be out of date. In revising it I didn't actually review any of the references WMC gave, however, my understanding has been that the changes in temperature usually aren't reported in low to mid latitude sediments (and similar proxies), but can be easily seen at high latitudes towards both poles. However, in retrospect I am probably understating the importantance of the HCO to low latitude climate change. My understanding has been that while there are not apparent changes in temperature at most low latitude sites, that there is abundant evidence of changes in precipitation and plant distributions suggesting significant changes in atmospheric circulation patterns and weather. I would presume that such circulation changes could affect temperatures at some local sites and perhaps that is the case at the Peruvian sites SEWilco is mentioning, however if my understanding is still accurate then any such low latitude temperature changes would be geographically limited anomalies and not part of the typical pattern. I will reiterate however that I am rather out of date on this issue so the consensus may well have shifted. Dragons flight 16:50, Mar 5, 2005 (UTC)

* Part of the difficulty in finding info is wading through all the studies around the North Atlantic, with all its complications due to three streams of different temperatures waving across the playing field, with stuff bouncing off the backstop Urals. For example, one study combined 500 pollen cores to find European regional changes — an impressive data processing task which not surprisingly shows variations across the area ("traditional" HCO warming over Northern Europe in summer). "The temperature of Europe during the Holocene reconstructed from pollen data" DOI:10.1016/S0277-3791(03)00173-2 (SEWilco)

I found this plot [3] which is similar to what I remember learning, but perhaps even more restricted. I would agree though that sorting through all the relavant recent studies would be an ugly mess. Dragons flight

* Undoubtedly there have been circulation changes as various limits were crossed. But at what point do many "local" circulation changes become a global effect? Are many climate changes around Amazonia considered as only an "Amazon region" effect, or considered as being a "South American continent" effect? And are changes in the Amazonian boreal winter Hadley cell regional, or a change in the global circulation of which it is a part? And is a global shift in the ITCZ merely a change in many local precipitation patterns? DOI:10.1098/rstb.2003.1434 (SEWilco)

It wouldn't surprise me if the circulation changes were reasonably global, though obviously it can be hard to establish that. Since apparently you are really looking into this, I will be interested to see how good a case you can find/build. Dragons flight

* It is inconvenient that there is so much landmass in the higher latitudes, so most low latitude sites are within "geographically limited" areas. (SEWilco 05:48, 6 Mar 2005 (UTC))

Well, I presume your interest is in comparing such past climate change to recent climate change. Unfortunately that does mean figuring out whether the effects were truly global. Obviously regional effects would still matter a great deal to people that happen to live in the affected region. I recall being told that the precipation related changes in Africa and Asia impacted where early humans chose to live, but I wasn't very certain about this so I didn't put it in. Dragons flight 07:34, Mar 6, 2005 (UTC)

[edit] Vostok plot

• (SEWilco) I haven't used IDL, but perhaps something like this would help the plot (and maybe xtickunits='time' or xtickformat='(I6)' on 'plot'?):

xyouts, 30000, -350, 'D-O events', charsize = 0.5, alignment = 0.5
plots, 30000, -355
plots, [27500,30000,28500], [-378,-355,-378], /continue
xyouts, 12500, -325, 'Younger Dryas', charsize = 0.5, alignment = 0.5
plots, 12500, -330
plots, 12500, -370, /continue
xyouts, 6000, -310, 'Optimum', charsize = 0.5
plots, 5000, -320
plots, [5000,7000,7000], [-315,-315,-320], /continue

[edit] Page move?

(William M. Connolley 14:30, 11 Mar 2005 (UTC)) Before too many links get created... shouldn't this be Holocene climatic optimum (no caps)?

• Depends on usage, and I started by following one usage. But I agree for several reasons. Somene will rename soon and add a redirect to deal with the capitalized form. I'd do it now but the WP DB is having difficulties and this can wait. (SEWilco 20:26, 11 Mar 2005 (UTC))

[edit] New pic: new text?

(William M. Connolley 23:51, 21 Mar 2005 (UTC)) With the new pic (thanks DF) there seems to be a need to revise the text (anyone for an extended hockey stick :-). The current:

The Holocene Climate Optimum warm event consisted of increases of up to 4 °C near the North Pole (in one study, winter warming of 3-9°C and summer of 2-6°C in northern central Siberia)[1] (http://en.wikipedia.org/wiki/Holocene_climatic_optimum#endnote_Koshkarova2004). Northwestern Europe experienced warming, while there was cooling in the south.[2] (http://en.wikipedia.org/wiki/Holocene_climatic_optimum#endnote_davis2003) The average temperature change appears to have declined rapidly with latitude so that essentially no change in mean temperature is reported at low and mid latitudes. Tropical reefs tend to show temperature increases of less than 1 °C. In terms of the global average, the typical shift was probably between 0.5 and 2 °C warmer than the mid-20th century (depending on estimates of latitude dependence and seasonality in response patterns).

no longer looks like a reasonable summary of the pic (or at least the first bit). Perhaps those interested need to see if they like the pic... one could perhaps quibble that simply averaging all the data is too simple. Or maybe its the best we can do for now. In particular, The Holocene Climate Optimum warm event consisted of increases of up to 4 °C near the North Pole (increases over what?) doesn't seem to fit: the max wiggles are +1.5.

But, if we were to accept the pic, then a better intro would, in my opinion, not pick out the most exciting T rises but start with the global picture and particularise. Thus it could start with something like:

The holocene (last 10kyr since end of ice age) has been, globally, a period of fairly stable temperatures. During the HCO, between 4-8 kyrBP, temperatures reached about 0.25 oC above 20C averages; late 20C temperatures exceed this... and then particularise.

So you're trying to fit the data to the picture? How did you get from '0.5 and 2' mid-20th century to 'about 0.25'? Because that's 0.25 of 20C average, while 0.5-2 is relative to 1950, the Origin of B.P.? (SEWilco 09:41, 22 Mar 2005 (UTC))

(William M. Connolley 10:10, 22 Mar 2005 (UTC)) No: I'm trying to fit the text of the page to the data in the picture. Mostly, to the thick black line for the overall picture. The thick black line gets about 0.25 oC above the 20C average. Individual records get higher, of course, but this is no surprise. But we're comparing them to the *global* 20C record. If you looked at individual stations you could find some even larger trends for 20C. I'm saying that the overall description should *start* from the global picture and work downwards - not start from the most exceptional records, which present a misleading impression of the degree of warmth then.

I think that depends on how one intends to define the HCO. If, as most people believe, the HCO is at best a regional phenomenon in terms of temperature, then I have no problem with starting from the local and extraordinary claims if one is willing emphasize that such changes are local and extraordinary, and then go on to say that the HCO probably only represented a mild warming on global scales. Dragons flight 16:57, Mar 22, 2005 (UTC)

HCO refers to the global warming event, mild or otherwise, not regional extremes. And you have run a poll on what most people believe about HCO? And how many HCO-peaking global sources do you need in Image:Holocene Temperature Variations.png in order for it to have been a global event? (SEWilco 22:07, 22 Mar 2005 (UTC))

To clarify, I meant that the HCO is generally regarded in the scientific literature as a major temperature event only at high northern latitudes, and perhaps a mild event on global scales. I don't object to leading off the article by describing the largest reported changes so long as it is properly qualified to indicate that on global scales it is usually believed to be more mild. Dragons flight 22:32, Mar 22, 2005 (UTC)

"Only"? Where else would one expect heat to cause a major temperature event other than where it is cold? Does a glacial era cause a major temperature event at the poles? I wouldn't expect equatorial and southern oceans to get much hotter without a lot of that heat being spread to higher latitudes. (SEWilco 06:54, 23 Mar 2005 (UTC))

[edit] Causes?

The milankovitch section (DF?) is completely unref'd. However I left it. I took out the sunspots pic, because (if we believe the M section) its irrelevant. It also doesn't seem to be ref'd in the text. William M. Connolley 20:25, 9 May 2006 (UTC)