Welcome to
Science a GoGo's
Discussion Forums
Please keep your postings on-topic or they will be moved to a galaxy far, far away.
Your use of this forum indicates your agreement to our terms of use.
So that we remain spam-free, please note that all posts by new users are moderated.


The Forums
General Science Talk        Not-Quite-Science        Climate Change Discussion        Physics Forum        Science Fiction

Who's Online
0 registered (), 372 Guests and 1 Spider online.
Key: Admin, Global Mod, Mod
Latest Posts
Top Posters (30 Days)
Topic Options
#16762 - 10/22/06 04:59 PM Medieval Warm Period?
samwik Offline
Megastar

Registered: 10/10/06
Posts: 1164
Loc: Colorado
I'm finding it hard to pin this down the date & extent of this "event." For example:

A humid event between AD 1100 and 1400 that peaked at AD 1300, was described by them as "coinciding with the known global Medieval Warm Period."
Schilman, B., Ayalon, A., Bar-Matthews, M., Kagan, E.J. and Almogi-Labin, A. 2002. Sea-land paleoclimate correlation in the Eastern Mediterranean region during the late Holocene. Israel Journal of Earth Sciences 51: 181-190.

vs.

The Medieval Warm Period (~ AD 875 to 1000) was categorized as the "warmest period" of the record, with temperatures about 0.25?C warmer than it is currently.
Pla, S. and Catalan, J. 2005. Chrysophyte cysts from lake sediments reveal the submillennial winter/spring climate variability in the northwestern Mediterranean region throughout the Holocene. Climate Dynamics 24: 263-278.

These dates don't even overlap!

...and from wikipedia, on the Little IceAge: "...Later (sect 33.5) discusses what the LIA actaully means. Porter (1986) uses 1250-1920...." This overlapps with the MWP "peak" of 1300 cited above!
These are ~"extreme" examples, but what are people referring to when they cite the MWP?
Thanks,
Samwik
_________________________
Pyrolysis creates reduced carbon! ...Time for the next step in our evolutionary symbiosis with fire.

Top
.
#16763 - 10/22/06 05:08 PM Re: Medieval Warm Period?
dehammer Offline
Megastar

Registered: 03/23/06
Posts: 1089
appearantly the sikipedia is wrong. thats what you get when just anyone can post things.

as i understand it:

the little ice age was from 1400 to 1180 give or take

the mediaval warming period was from 700 to 1400
_________________________
the more man learns, the more he realises, he really does not know anything.

Top
#16764 - 10/22/06 07:24 PM Re: Medieval Warm Period?
samwik Offline
Megastar

Registered: 10/10/06
Posts: 1164
Loc: Colorado
Wiki is working on it; it talks about the many LIA discrepancies, and I pulled the one item that conflicted with the two independant MWP sources that I found in regular journals (Climate Dynamics and Israel Journal of Earth Sciences). Those two conflicting sources were my main surprise.
~samwik
_________________________
Pyrolysis creates reduced carbon! ...Time for the next step in our evolutionary symbiosis with fire.

Top
#16765 - 10/22/06 09:26 PM Re: Medieval Warm Period?
terrytnewzealand Offline
Megastar

Registered: 08/02/06
Posts: 1031
Loc: Whangarei New Zealand
It seems a change to cooler at 1400 is pretty well accepted. It slowed Polynesian migration in the Pacific as well as Viking travel in the North Atlantic. When Cook arrived in NZ about 1770 glaciers in SI reached the sea. They have contracted considerably since then but expand a little occasionally.

Top
#16766 - 10/23/06 12:20 AM Re: Medieval Warm Period?
RicS Offline
Senior Member

Registered: 03/26/06
Posts: 310
Loc: Sydney, Australia
G'day,

There is no single Medieval Warm Period nor is there any single Little Ice Age. Depends on what is being used as evidence, who believes what and what your definition is.

The Little Ice Age is a general term for three cooler periods lasting until as late as 1880, depending on the definition. It starts around 1350 or 1400. The three cooler periods are fairly well delineated for Europe but much harder to pin down for other areas of the world. In Europe, where any cooler period is going to have a profound effect because of the marginal nature of much of the area, the LIA bit very deep, causing prolonged famine and stifled technological advancement. Depending on who you wish to believe, the Industrial Revolution took off only when it got warmer because it got warmer. But that is a sociological question much more than a climate one.

The Medieval Warm Period certainly does not start at 700AD but there are records that suggest it may have started before 900AD.

We've discussed this before but it depends on how tree rings, ocean sediments or ice cores are read, as well as evidence such as paintings etc.

Tree rings are what where used for the Mann "hockey stick" attempting to show there was almost no Mediaval Warm Period or LIA. Then again, even though tree rings are lousy temperature indicators, the Mann et al study only used selected tree ring studies and only those that resulted in almost no warm period or cold period prior to the 20th century.

Tree rings are very good for overall good or bad seasons whatever the reason and so they do provide very broad brush trends but are way too open to interpretation to get down to whether a particular period was warmer than another. Ice cores have the very big disadvantage of being where it is very cold all year round plus the physics of just how you determine temperature from ice cores is much murkier than some researchers would have the general community believe.

The Medieval Warm Period also does not appear to be the warmest period of record with a very warm period around 6,000 years ago and around 8,000 years ago plus a period that may have been warm at the beginning of the Roman Empire. The earlier warm period is sometimes referred to as the peak of the Holocene or the Bronze Warm Period. And evidence in that period suggests this was very hot indeed, with glaciar retreat much more pronounced than today, much hotter overall temperatures (both anecdotal evidence and debris evidence in glacial paths etc).

I actually saw an argument that the Medieval Warm Period did not exist at all citing the presence of 50 vineyards in Southern England in the alleged warm period but 350 today. Of course, the ones today are there because they are using modern technology, special species of grapes, etc, etc, but that did not seem to bother the scientists making this argument.

While the dates are very difficult to pin down, Terry mentions something that is often disputed about the periods. That is that it was or wasn't world wide. Yet Vikings were able to grow produce in Greenland, China's agriculture flourished in colder areas, the South Seas and New Zealand had two distinct climate bands of warmer and colder, what is now Canada and the US had similar bands. They don't match up all that well for pretty much the same reasons as the evolution and extinction of particular dinasaurs is often not much more than a guess, the evidence is scattered and not sufficient to create a consistent record.

This is just another topic that can be endlessly debated and studies can be found that support pretty much any position, especially since this went from a purely academic interest to a very political one. "Proving" that this current period is the hottest has became a big issue. Obviously if the Holocene has had warmer periods previously then this period becomes less significant and less likely to to be man made. So a pretty large effort to play down the Bronze Warm Period, the Medieval Warm Period and to suggest the LIA was just regional started cropping up in research papers not all that long ago and has been accelerating at a remarkable rate.

It still all boils down to the data for the research. In the case of any period prior to 1880, the data is indirect. It comes from the sources previously mentioned. These sources are not particularly reliable. The less reliable the source the more open a subject is to endless conjecture. It amazes me, for instance, that Mr Gore uses the "hockey stick" curve and that it still enjoys significant support despite the research being shown to have been selective in the extreme.

If this thread does not devolve into yet another "tit for tat" argument, I'll be happy to provide a few links to various research on this subject. The ones I've found the most enlightening are actually the ones that are being used to attempt to downplay the periods. I think I've mentioned Professor Thompson's tropical glacial ice cores a few times now and the brilliance of getting six vastly different results and averaging them.


Regards


Richard
_________________________
Sane=fits in. Unreasonable=world needs to fit to him. All Progress requires unreasonableness

Top
#16767 - 10/23/06 03:12 AM Re: Medieval Warm Period?
DA Morgan Offline
Megastar

Registered: 10/17/04
Posts: 4136
Loc: Seattle, WA
884 words ... not a single link anyone can follow to verify if there is any substance to your remarks.

Is it because there is no substance and you don't want any to be able to check?

Or because you have links but intentionally choose to not share them?
_________________________
DA Morgan

Top
#16768 - 10/23/06 07:57 AM Re: Medieval Warm Period?
terrytnewzealand Offline
Megastar

Registered: 08/02/06
Posts: 1031
Loc: Whangarei New Zealand
Oh, come on DA and RicS. Let's just confine this to discussion to Holocene fluctuations and little ice age and Medieval warm period. Interesting subjects in their own right. There has been a heap of work done on pollen profiles in NZ swamps. They don't directly tell us about the climate but do tell us what type of vegetation occurred nearby, thus giving us some idea of temperature and rainfall. Here's the first one i found:

http://geovoice.otago.ac.nz/issue001/mvandergoes.html

Of course humans had a huge influence on the vegetation when they arrived.

Top
#16769 - 10/23/06 09:13 AM Re: Medieval Warm Period?
samwik Offline
Megastar

Registered: 10/10/06
Posts: 1164
Loc: Colorado
Thanks Richard, that's a lot to read; but I'll get to it. I've been elsewhere (Origins) wink today.
~Sam

P.S. okay, nice overview. Thanks again....
~SA
_________________________
Pyrolysis creates reduced carbon! ...Time for the next step in our evolutionary symbiosis with fire.

Top
#16770 - 10/23/06 03:06 PM Re: Medieval Warm Period?
RicS Offline
Senior Member

Registered: 03/26/06
Posts: 310
Loc: Sydney, Australia
G'day Terry,

Actually I thought I was confining my comments to the Holocene fluctuations. Its a bit hard not to mention the politics of how that is determined, however, because the science doesn't exist in a vacuum.

But it was a general query and I thought it deserved a general answer. As Mr Morgan says right now I'm not prepared to post a bunch of links or citations because the whole thing devolves into an endless debate about such specifics as to how many words I manage to type.

This is one field where there is a great deal of research which can be referred to. How about you pick a subject to start with and I'll be happy to contribute specific research or links. It's too wide a subject currently. For instance, the physics of ice core samples could be discussed. There are several research papers on this as well as what the ice core samples are interpreted to be. Dr Singer rather likes sedimentation samples for determining trends in this climate. That's not a bad topic either.

We could discuss the Mann et al graph and similar downplaying of the peaks and troughs of the Holocene and there is certainly reasonable links to research ranging from complete support to total repudiation. I guess that is what these types of forums are for, if you are interested in a scientific subject, really to learn other's views and why they are held and whether they have a scientific basis. Actually, sometimes suppositions that even the proposer does not support result in terrific results in such discussions but they really do need to be treated with a view that the reason to discuss such topics is to learn other viewpoints, rather than prove that yours is the only view worthy of recognition, imho.

I liked your link by the way. It is a study that sets outs its aims well and confines both the research and the conclusions to those aims. There are thousands of such studies around. Good quality studies that help with an overall understanding of the general trends of climate during the Holocene and what was the local response to climate. In this instance the study also makes the distinction between what is known and possible alternative reasons, such as the change in precipitation levels.

The study also demonstrates why you end up with so many different dates for different periods of the Holocene. Climate may change quickly but vegetation, the subject of this subject, takes a considerable time to adapt to the changes unless really extreme. So you get a broad brush idea of what climate changes might have occurred but not a great time frame.

To be a little political again, I wonder what the conclusion of this study would have read like if it had not been done ten years ago.
_________________________
Sane=fits in. Unreasonable=world needs to fit to him. All Progress requires unreasonableness

Top



Newest Members
debbieevans, bkhj, jackk, Johnmattison, RacerGT
865 Registered Users
Sponsor
Facebook

We're on Facebook
Join Our Group

Science a GoGo's Home Page | Terms of Use | Privacy Policy | Contact Us
Features | News | Books | Physics | Space | Climate Change | Health | Technology | Natural World

Copyright © 1998 - 2016 Science a GoGo and its licensors. All rights reserved.