Yelling,
Our discussion has been over a few key questions:
1. Was the Medieval warming period a discernable climate anomaly? Was it global in its extent?
2. Was the LIA (Little Ice Age) a discernable climate anomaly? Was it global in its extent?
3. Is there an observable anomoly in the 20th century that is most extreme? Are recent temperatures the highest in a millenia?
There is no debate that LIA and MWP existed at some level, the debate is whether it is global in extent enough to show in the kind of global or hemispheral reconstruction such as Mann made.
Soon and Baliunas, Climate Research Vol 23:89-110, 2003, ask and answer the 3 questions under discussion here directly, with a number of studies from around the world.
http://guisun3.gkss.de/G/Mitarbeiter/storch/pdf/soon+baliunas.cr.2003.pdf
We could gainsay back and forth, but my own sense, which is what the S+B paper states well and backs with over 130 studies, is this:
1. The MWP (warming period of 800-1300) was a real climactic anomaly and was global in extent.
2. The LIA (little ice age of 1300-1900, particularly at in 17th century) was a real climactic anomaly and was global in extent, with temperatures lower than present day.
3. There has been significant warming in the 19th and 20th centuries, but temperature level is not unique to the past millenium. We cant say with any confidence that recent temperatures are the warmest in 1000 years, or warmer than the MWP.
Having just read S+B, I'd just reference that and call it a day. As a PhD in another field (Comp Sci), I am a layperson with a good BS detector. I've read Mann, M+M, and S+B in the past 3 days. Of the papers, S+B impresses me the most as being clearest, most informative, and easiest to verify. The references I have looked at DO verify what they say; it's solid. The Mann work leaves way too many hidden variables and has a suspect way of merging proxy data; this is exactly what M+M is attacking them on. This lack of reproducibility is IMHO bad way to write papers and do science; that he has defenders attacking M+M is a sad commentary on politics trumping good scientific practice here. Anyway, S+B notes general issues with the concept of merging such data (See S+B on page p. 104); the global climate is not a homogeneous entity but a merging of regional climates. Better to take the timelines as individual representations for a regional or local climate. This reduces biasing errors that occurs with wieghting of different proxies.
It also puts in context these other papers that constitute those regional data points, which frankly are rabbit trails in our discussion ...
"The abstract to this paper says: “The results show that over the past 500 years, the investigated areas have on average warmed 1 K, with more than half of the warming occurring in the 20th century alone, and 70–80% in the 19th and 20th centuries taken together.” That sounds pretty clear to me and it would see that the borehole reconstruction in Russia does not support your claim that they put “Mann's work and his easy-to-munge-into-your-preconceived-conclusions-PCA to shame.” (your words)
----
This is consistent with the LIA hypothesis and other studies that show cooler temperatures in 15th-18th century (LIA) and warmer trend in 19th and 20th.
This borehole tells us well what happened to temperature (give or take some error margin in measurement) in this region. Climate changes (eg jet stream, humidity change etc.) may make a region warmer even if the globe is cooling, but it's a data point. (viz. your Keigwin cite.)
Collating the regional pictures is the best way to get a global picture, which is what S+B did. Of the over 100 studies that covered the timescales in question, only a tiny fraction (less than 5%) were inconsistent with the hypothesis of LIA and MWP. On the other hand, the majority of studies and were NOT consistent with the hypothesis that 20th century temperatures were the highest in 1000 years.
As abstract of S+B states, "Across the world, many records revealt that the 20th century is probably not the warmest nor a uniquely extreme climatic period of the last millenium."
... this does not btw invalidate global warming as a hypothesis or invalidate that humans can impact climate, it just invalidates the incorrect extrapolation of Mann's work into the non-error-bar'd 'hockey stick' as unfounded speculation.
As I said, I'll leave it at that: LIA and MWP have more climate science and studies to back them up than the 'hockey stick'.
Since S+B are stating what I've pretty much concluded independently, I'll let that be the 'authority' on my side and end it. I know its had its share of controversy, due to the politicization of this area ...
http://sciencepolicy.colorado.edu/prometheus/archives/climate_change/000219scientists_and_the_p.html
... but we wont resolve that here anyway.
Press Release on the Soon+Baliunas paper:
http://cfa-www.harvard.edu/press/pr0310.html
Release No.: 03-10
For Release: March 31, 2003
20th Century Climate Not So Hot
Cambridge, MA - A review of more than 200 climate studies led by researchers at the Harvard-Smithsonian Center for Astrophysics has determined that the 20th century is neither the warmest century nor the century with the most extreme weather of the past 1000 years. The review also confirmed that the Medieval Warm Period of 800 to 1300 A.D. and the Little Ice Age of 1300 to 1900 A.D. were worldwide phenomena not limited to the European and North American continents. While 20th century temperatures are much higher than in the Little Ice Age period, many parts of the world show the medieval warmth to be greater than that of the 20th century.
Smithsonian astronomers Willie Soon and Sallie Baliunas, with co-authors Craig Idso and Sherwood Idso (Center for the Study of Carbon Dioxide and Global Change) and David Legates (Center for Climatic Research, University of Delaware), compiled and examined results from more than 240 research papers published by thousands of researchers over the past four decades. Their report, covering a multitude of geophysical and biological climate indicators, provides a detailed look at climate changes that occurred in different regions around the world over the last 1000 years.
"Many true research advances in reconstructing ancient climates have occurred over the past two decades," Soon says, "so we felt it was time to pull together a large sample of recent studies from the last 5-10 years and look for patterns of variability and change. In fact, clear patterns did emerge showing that regions worldwide experienced the highs of the Medieval Warm Period and lows of the Little Ice Age, and that 20th century temperatures are generally cooler than during the medieval warmth."
Soon and his colleagues concluded that the 20th century is neither the warmest century over the last 1000 years, nor is it the most extreme. Their findings about the pattern of historical climate variations will help make computer climate models simulate both natural and man-made changes more accurately, and lead to better climate forecasts especially on local and regional levels. This is especially true in simulations on timescales ranging from several decades to a century.
Historical Cold, Warm Periods Verified
Studying climate change is challenging for a number of reasons, not the least of which is the bewildering variety of climate indicators - all sensitive to different climatic variables, and each operating on slightly overlapping yet distinct scales of space and time. For example, tree ring studies can yield yearly records of temperature and precipitation trends, while glacier ice cores record those variables over longer time scales of several decades to a century.
Soon, Baliunas and colleagues analyzed numerous climate indicators including: borehole data; cultural data; glacier advances or retreats; geomorphology; isotopic analysis from lake sediments or ice cores, tree or peat celluloses (carbohydrates), corals, stalagmite or biological fossils; net ice accumulation rate, including dust or chemical counts; lake fossils and sediments; river sediments; melt layers in ice cores; phenological (recurring natural phenomena in relation to climate) and paleontological fossils; pollen; seafloor sediments; luminescent analysis; tree ring growth, including either ring width or maximum late-wood density; and shifting tree line positions plus tree stumps in lakes, marshes and streams.
"Like forensic detectives, we assembled these series of clues in order to answer a specific question about local and regional climate change: Is there evidence for notable climatic anomalies during particular time periods over the past 1000 years?" Soon says. "The cumulative evidence showed that such anomalies did exist."
The worldwide range of climate records confirmed two significant climate periods in the last thousand years, the Little Ice Age and the Medieval Warm Period. The climatic notion of a Little Ice Age interval from 1300 to1900 A.D. and a Medieval Warm Period from 800 to 1300 A.D. appears to be rather well-confirmed and wide-spread, despite some differences from one region to another as measured by other climatic variables like precipitation, drought cycles, or glacier advances and retreats.
"For a long time, researchers have possessed anecdotal evidence supporting the existence of these climate extremes," Baliunas says. "For example, the Vikings established colonies in Greenland at the beginning of the second millennium that died out several hundred years later when the climate turned colder. And in England, vineyards had flourished during the medieval warmth. Now, we have an accumulation of objective data to back up these cultural indicators."
The different indicators provided clear evidence for a warm period in the Middle Ages. Tree ring summer temperatures showed a warm interval from 950 A.D. to 1100 A.D. in the northern high latitude zones, which corresponds to the "Medieval Warm Period." Another database of tree growth from 14 different locations over 30-70 degrees north latitude showed a similar early warm period. Many parts of the world show the medieval warmth to be greater than that of the 20th century.
The study - funded by NASA, the Air Force Office of Scientific Research, the National Oceanic and Atmospheric Administration, and the American Petroleum Institute - will be published in the Energy and Environment journal. A shorter paper by Soon and Baliunas appeared in the January 31, 2003 issue of the Climate Research journal.
You raise a number of interesting points. However they seem to be based mostly on the Soon and Bilanius paper in Climate Research. While this paper does contain a number of references, they turn out to be the type we were already dealing with. For example they use Keigwin to show that the Sargasso had cooler temperatures during the LIA without mentioning that Keigwin thinks this is due to a shift of currents. And they use deMenocal work to show cooling without noting that this was also due to a shift in currents and more upwelling.
There are a number of problems with this paper. As an example, they present the following in their methodology (this is a direct quote, please check me if you don’t believe it ) “Table 1 and Figs. 1 to 3 summarize the answers to the questions posed here about local climatic anomalies. For Questions (1) and (2), we answered ‘Yes’ if the proxy record showed a period longer than 50 yr of cooling, wetness or dryness during the Little Ice Age, and similarly for a period of 50 yr or longer for warming, wetness or dryness during the Medieval Warm Period.”
Read that again!!!!!!!! So if the record is warm OR wet OR dry it supports a warm spell. And if the record is cold OR wet OR dry it supports a cold spell. Consequently any change in precipitation (wet or dry) can support either warm or cold. Add to that the fact that they did not try to establish the magnitude of either warming or cooling. Not surprising this paper did create a lot of stir in the field at the time.
However this was not for the politics but for the bad science. In fact, the Publishers of Climate Reaearch (the journal who published this) had to print a retraction that says:
“Major conclusions of Soon & Baliunas are: ‘Across the world, many records reveal that the 20th century is probably not the warmest nor a uniquely extreme climatic period of the last millenium.’ (p. 89) and ‘Overall, the 20th century does not contain the warmest anomaly of the past millennium in most of the proxy records which have been sampled world-wide’ (p. 104). While these statements may be true, the critics point out that they cannot be concluded convincingly from the evidence provided in the paper. CR should have requested appropriate revisions of the manuscript prior to publication.” In other words, it is an opinion with no science to back it up! It is very rare for a publisher to have to do this and it led to a change in the way CR reviews papers.
If you are interested in an overview of the topic I would refer you to this article:
http://w3g.gkss.de/G/Mitarbeiter/storch/CR-problem/Chronicle%20of%20Higher%20Education.030904.pdf
Anyway, in regards to S&B vs Mann, I will be pleased to stick with Mann. S&B’s work is interesting but from it they can conclude nothing!. I can’t see how you can state that it is solid? Mann’s methodology is complex but it is a complex subject and it is far, far less subjective than S&B’s work.