Linking the ENSO and PDO induced rainfall of the Pacific Northwest to proxy data in tree rings and lake sediments

Castor Lake, one of the lakes where sediments samples used in this study were taken from. Credit: University of  Pittsburgh

From Penn State , another Mann paper with proxy sets, and a divergence problem. At least they are talking about the MWP, or as they call it, the Medieval Climate Anomaly which had been erased in previous papers Mann had been involved with. The attempt to link paleo data to the PDO is interesting too. Mann was not lead author, and hopefully none of the flawed PCA math he’s used to mess up other papers made it into this one. I’m hopeful, as the SI contains some equations/code.

The gist of the paper is this: they wanted to determine patterns of drought in the Pacific Northwest, so the authors used proxy data obtained both from tree rings and from oxygen isotopes related to lake sediments.

According to lead author Byron Steinman.“The data matched up on a short-term, decadal scale, however, on a longer-term, century scale, the records diverged. The tree-ring data suggests dry conditions during the Medieval Climate Anomaly summers while the isotope data suggest wetter-than-expected winters.”

New methods help scientists shed light on ancient climates

Tree ring and oxygen isotope data from the U.S. Pacific Northwest do not provide the same information on past precipitation, but rather than causing a problem, the differing results are a good thing, according to a team of geologists.

The researchers are trying to understand the larger spatial patterns and timing of drought in the arid and semiarid areas of the American West.

“We generally understand that the Medieval Climate Anomaly, a warm period in much of the northern hemisphere that occurred about 950 to 1250 was a dry period in the American West,” said Byron A. Steinman, postdoctoral researcher in meteorology, Penn State. “But there is complexity to the patterns of drought and it may not have been dry in winter in the Pacific Northwest.”

East of the Cascade Mountains, the Pacific Northwest is dry and hot in the summer and wet in the winter now.

Estimates of past precipitation are made from proxies like tree rings, which can record amounts of precipitation and temperature. But tree rings are better at recording what happens during the spring and summer, when the tree is growing, than in the winter when the tree is not.

Steinman, who worked with Mark B. Abbott, professor of geology and planetary science, University of Pittsburgh, his Ph.D. advisor, looked at oxygen isotopes found in 1,500 years of sediment at the bottom of lakes. The isotopic composition of these sediments can reflect the amount of water that enters the lake, especially during the wet season.

The analyzed lake sediments contain calcium carbonate in the form of calcite. The oxygen isotope ratios in this mineral relate directly to the isotope ratio of water in the lake. The researchers looked at sediment from two small lakes in Washington state. Castor Lake is on a plateau and water inflow is only from precipitation and groundwater. This lake has no outflow, so most water loss is through evaporation. Lime Lake, on the other hand, loses the majority of water through a permanent outflow stream, although all water enters in the same manner as for Castor Lake. By comparing the two lakes, the researchers could determine the water balance between evaporation and precipitation.

The researchers looked at two stable isotopes of oxygen — oxygen 16 and oxygen 18 — in the sediments. Oxygen 16 is lighter than oxygen 18, so during evaporation and lake draw down, more oxygen 16 evaporates out and the calcite in the sediments contain more oxygen 18. If the lakes are full of water, then there will be more oxygen 16 in the calcite. The layers of sediment that are laid down each year can be dated either by using carbon 14 dating of organic material or by locating layers of tephra — volcanic ash, that signifies known — dated volcanic eruptions. In this way, the researchers could pinpoint when drought occurred.

“The tree ring data and isotope data match up on a short term, decadal scale,” said Steinman. “On a longer term, century scale, the records diverge.”

While the decadal ups and down remain the same for both proxies, when viewed on a 100-year or longer scale, the proxies show differences. The tree ring data suggest dry conditions during the Medieval Climate Anomaly summers, while the isotope data suggests wetter than expected winters.

Comparing the lake sediment records to existing records of the Pacific Decadal Oscillation, a warming or cooling of the coastal waters off the Pacific Northwest, the researchers report in the current online issue of the Proceedings of the National Academy of Sciences “a strong centennial timescale relationship over the past 1,500 years between winter precipitation amounts in eastern Washington and Pacific Decadal Oscillation temperature anomalies.”

The PDO is linked to the El Nino Southern Oscillation, a tropical phenomenon that influences global weather patterns. During and before the Medieval Climate Anomaly, the North Pacific Ocean was warmer and Washington had greater precipitation than during the Little Ice Age, which occurred from about 1450 to 1850, when there was less precipitation.

Steinman used a previously published and validated model based on established lake physics and modern recorded precipitation and temperature to determine the amounts of rainfall indicated by the isotopic record

“The best thing we could do now is to produce additional quantitative precipitation records, this time with different lake systems,” said Steinman.

###

Other researchers on this project were Michael E. Mann, professor of meteorology and geosciences and director of the Penn State Earth System Science Center; Nathan D. Stansell, former Ph.D. student at the University of Pittsburgh, now a research fellow, Byrd Polar Research Center, Ohio State University and Bruce Finney, professor of biological sciences, Idaho State University.

The National Science Foundation funded this research.

=============================================================

Paper: 1500 year quantitative reconstruction of winter precipitation in the Pacific Northwest, by Byron A. Steinman, Mark B. Abbott, Michael E. Mann, Nathan D. Stansell, and Bruce P. Finney, PNAS, 2012.

Abstract

Multiple paleoclimate proxies are required for robust assessment of past hydroclimatic conditions. Currently, estimates of drought variability over the past several thousand years are based largely on tree-ring records. We produced a 1,500-y record of winter precipitation in the Pacific Northwest using a physical model-based analysis of lake sediment oxygen isotope data. Our results indicate that during the Medieval Climate Anomaly (MCA) (900–1300 AD) the Pacific Northwest experienced exceptional wetness in winter and that during the Little Ice Age (LIA) (1450–1850 AD) conditions were drier, contrasting with hydroclimatic anomalies in the desert Southwest and consistent with climate dynamics related to the El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO). These findings are somewhat discordant with drought records from tree rings, suggesting that differences in seasonal sensitivity between the two proxies allow a more compete understanding of the climate system and likely explain disparities in inferred climate trends over centennial timescales.

Advertisements

  Subscribe  
newest oldest most voted
Notify of
Ulf T

“The tree ring data and isotope data match up on a short term, decadal scale,” said Steinman. “On a longer term, century scale, the records diverge.”
The article itself is behind a paywall, so I wonder: in most other reconstructions (e.g. MBH98, Gergis et al, …), tree ring series are screened for correlation with the actual temperature record, and series that don’t match up on a short term are simply excluded.
If this paper does the same, shouldn’t the above read “we only look at data that match up on a short term. On a longer term, century scale, the records diverge”?

…the proxies show differences. The tree ring data suggest dry conditions during the Medieval Climate Anomaly summers, while the isotope data suggests wetter than expected winters.
The proxy for *summer* conditions indicates the summers were dry and the proxy for *winter* conditions indicates that winters were wet — why was that an unexpected development?

“the Medieval Climate Anomaly which had been erased in previous papers Mann had been involved with. “
Hardly erased. Mann’s 2008 PNAS paper says, for example:
“The EIV reconstructions suggest that temperatures were relatively warm (comparable with the mean over the 1961–1990 reference period but below the levels of the past decade) from A.D. 1000 through the early 15th century, then fell abruptly. By contrast, the CPS reconstructions indicate more uniformly colder conditions, with peak Medieval warmth that does not breach the mean warmth of modern reference period (1961–1990), and a long-term, more steady decline in temperatures before 20th century warming.”

I have not read the paper, but from the abstract one might ask if it was proven or assumed that calcite growth and chemistry had reached equilibrium. 1,500 years is but a blink in geology.
The authors note “Tree ring and oxygen isotope data from the U.S. Pacific Northwest do not provide the same information on past precipitation, but rather than causing a problem, the differing results are a good thing, according to a team of geologists.”
This is more commendable that the belief of the Australian Prime Minister, who says that there will be more wet periods and more droughts. Sure, these differning results are a good thing, on average.

Mike M

“The tree ring data suggest dry conditions during the Medieval Climate Anomaly summers, while the isotope data suggests wetter than expected winters.”
Isn’t that sort of a way to say that the two agree with each other but make it sound as though they don’t?

Nick Stokes,
I would be careful about citing Mann08. It’s been debunked, you know. Tiljander.

Louis Hooffstetter

“The tree ring data and isotope data match up on a short term, decadal scale. On a longer term, century scale, the records diverge.”
Translation: Tree ring and/or lake sediment isotope data appear to suck as climate proxies, but we don’t know which one or why.
Two thoughts:
1. How ironic is it that Mann co-authors a paper that refutes his steadfast faith in tree rings as temperature proxies?
2. Hats off to Byron Steinman for being truthful. I suspect his life expectancy as a climatologist will be short.

Ian H

“Medieval Climate Anomaly” – I guess this is what used to be called the medieval warm period or MWP. But of course we can’t use word “warm” as it would be politically incorrect.
PC science. Oh joy.

polistra

“Expected” on the basis of theory as usual. If you’re going to “expect” something logically and rationally, you should look at facts instead of theory.
Fact: In this part of the country, winters are the wet season. Most of the precip falls in winter. That holds true in cooler times like the ’80s and in warmer times like the 2000s. So you should “expect” it to hold true in another warmer time like the 1100s.

When did the MCA start getting used? I see some Google refs to 2009, e.g.
http://www.co2science.org/articles/V12/N27/EDIT.php :

In a paper recently published in Science, Trouet et al. (2009) tell how they constructed a 947-year history (AD 1049-1995) of the North Atlantic Oscillation (NAO), using a tree-ring-based drought reconstruction for Morocco (Esper et al., 2007) and a speleothem-based precipitation proxy for Scotland (Proctor et al., 2000). This history begins in the midst of what they call the Medieval Climate Anomaly (MCA), which they describe as “a period (~ AD 800-1300) marked by a wide range of changes in climate globally [our italics],” which interval of medieval warmth, as they describe it, is “the most recent natural counterpart to modern warmth and can therefore be used to test characteristic patterns of natural versus anthropogenic forcing.”

(Sorry, too lazy to put there italics back in.)
Then there’s this from Google:

Scholarly articles for “Medieval Climate Anomaly”
… of the Little Ice Age and Medieval Climate Anomaly – Mann – Cited by 202
… mode dominated the medieval climate anomaly – Trouet – Cited by 174
… drought pattern during the Medieval Climate Anomaly – Helama – Cited by 26

Ah yes, I’d forgotten that the coiners of the MCA kept the LIA. Scumbags.
Hmm, that wasn’t very nice of me. Perhaps “Rogue’s list” will do:

Science 27 November 2009:
Vol. 326 no. 5957 pp. 1256-1260
DOI: 10.1126/science.1177303
Report
Global Signatures and Dynamical Origins of the Little Ice Age and Medieval Climate Anomaly
Michael E. Mann1,*,
Zhihua Zhang1,
Scott Rutherford2,
Raymond S. Bradley3,
Malcolm K. Hughes4,
Drew Shindell5,
Caspar Ammann6,
Greg Faluvegi5 and
Fenbiao Ni4
+ Author Affiliations
1Department of Meteorology and Earth and Environmental Systems Institute, Pennsylvania State University, University Park, PA 16802, USA.
2Department of Environmental Science, Roger Williams University, Bristol, RI 02809, USA.
3Department of Geosciences, University of Massachusetts, Amherst, MA 01003–9298, USA.
4Laboratory of Tree-Ring Research, University of Arizona, Tucson, AZ 85721, USA.
5NASA Goddard Institute for Space Studies, New York, NY 10025, USA.
6Climate Global Dynamics Division, National Center for Atmospheric Research, Boulder, CO 80305, USA.
*To whom correspondence should be addressed. E-mail: mann@meteo.psu.edu
Abstract
Global temperatures are known to have varied over the past 1500 years, but the spatial patterns have remained poorly defined. We used a global climate proxy network to reconstruct surface temperature patterns over this interval. The Medieval period is found to display warmth that matches or exceeds that of the past decade in some regions, but which falls well below recent levels globally. This period is marked by a tendency for La Niña–like conditions in the tropical Pacific. The coldest temperatures of the Little Ice Age are observed over the interval 1400 to 1700 C.E., with greatest cooling over the extratropical Northern Hemisphere continents. The patterns of temperature change imply dynamical responses of climate to natural radiative forcing changes involving El Niño and the North Atlantic Oscillation–Arctic Oscillation.

Are they expressing surprise that rainfall could substantially different trends in different seasons on a centennial timescale? They shouldn’t be surprised such a thing could happen at all! It’s just happened over the entire US in the last century or so! Specifically, only one season shows precipitation increases from 1895 to the present of any magnitude close to being significant: Fall. For the US average, every other season is flat: basically zero trend. Clearly for whatever reason, nature can decide to arbitrarily partition long term rainfall trends by season. One doesn’t need questionable proxy evidence for this: one has the observed precipitation record!

Even this lay person knows that there are papers demonstrating the global nature of the MWP. So how on earth do they think that they can get away with “the Medieval Climate Anomaly, a warm period in much of the northern hemisphere”?
http://pages.science-skeptical.de/MWP/MedievalWarmPeriod1024x768.html

The earliest WUWT reference may be from 2008, see http://wattsupwiththat.com/2008/08/23/another-chance-to-make-comments-on-climate-change/#comment-33452
There are several references from 2009, here are a few links:
http://wattsupwiththat.com/2009/03/31/dr-roger-pielke-senior-support-for-cato-letter-and-advertisement/#comment-109718 points us to http://www.sciencemag.org/content/324/5923/78.abstract which starts with:

Science 3 April 2009:
Vol. 324 no. 5923 pp. 78-80
DOI: 10.1126/science.1166349
Report
Persistent Positive North Atlantic Oscillation Mode Dominated the Medieval Climate Anomaly
Valérie Trouet1,*,
Jan Esper1,2,
Nicholas E. Graham3,4,
Andy Baker5,
James D. Scourse6 and
David C. Frank1
+ Author Affiliations
1 Swiss Federal Institute for Forest, Snow, and Landscape Research (WSL), Zürcherstrasse 111, 8903 Birmensdorf, Switzerland.
2 Oeschger Centre for Climate Change Research, Erlachstrasse 9a, 3012 Bern, Switzerland.
3 Hydrologic Research Center, 12780 High Bluff Drive, Suite 250, San Diego, CA 92130–2069, USA.
4 Scripps Institution of Oceanography, 9500 Gilman Drive, La Jolla, CA 92093–0225, USA.
5 School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, B15 2TT, UK.
6 School of Ocean Sciences, University of Wales Bangor, Menai Bridge, Anglesey, LL59 5AB, UK.
* To whom correspondence should be addressed. E-mail: trouet@wsl.ch
Abstract
The Medieval Climate Anomaly (MCA) was the most recent pre-industrial era warm interval of European climate, yet its driving mechanisms remain uncertain. We present here a 947-year-long multidecadal North Atlantic Oscillation (NAO) reconstruction and find a persistent positive NAO during the MCA. Supplementary reconstructions based on climate model results and proxy data indicate a clear shift to weaker NAO conditions into the Little Ice Age (LIA). Globally distributed proxy data suggest that this NAO shift is one aspect of a global MCA-LIA climate transition that probably was coupled to prevailing La Niña–like conditions amplified by an intensified Atlantic meridional overturning circulation during the MCA.

Hmm, that article was cited by: “The Rhone Glacier was smaller than today for most of the Holocene Geology 1 July 2011: 679-682.” Interesting. That glacier was the first one where iceflow was studied.
http://wattsupwiththat.com/2009/11/26/mann-has-a-new-paper-he-apparently-discovers-the-medieval-warm-period/ says:

Mann and his colleagues reproduced the relatively cool interval from the 1400s to the 1800s known as the “Little Ice Age” and the relatively mild conditions of the 900s to 1300s sometimes termed the “Medieval Warm Period.”
“However, these terms can be misleading,” said Mann. “Though the medieval period appears modestly warmer globally in comparison with the later centuries of the Little Ice Age, some key regions were in fact colder. For this reason, we prefer to use ‘Medieval Climate Anomaly’ to underscore that, while there were significant climate anomalies at the time, they were highly variable from region to region.”

theduke

The “MWP” is now the “MCA.” Because they say so. And yet it lasted for 300 years.
Which also raises the obvious question: if there was a Medieval Climate Anomaly, why can’t their be a naturally occurring Modern Climate Anomaly?
Anyone?

Steve C

“Medieval Climate Anomaly” … Ah, yes, that would be the Mediaeval Climate Optimum, I presume … but of course ‘some’ people could never call it that. D#mn this Newspeak!

Ian H says:
July 5, 2012 at 4:53 am
“Medieval Climate Anomaly” – I guess this is what used to be called the medieval warm period or MWP. But of course we can’t use word “warm” as it would be politically incorrect.
PC science. Oh joy.

Obviously, to anyone with an historical perspective, we have warm periods and cool periods. But to the Acolytes of Climate Science, any deviation from the long, smooth handle of the Icon of the Hockey Stick would be heresy. Never mind that the Medieval Warm Period is a well-established term among climatologists. If it must be acknowledged at all, then it must be an ‘anomaly’. Climate is not supposed to change, because change is evil and besides, man is responsible.
If these ideologues were not responsible for so much misspent effort (and dollars), they would be laughable.
/Mr Lynn

@Nick Stokes
> Hardly erased …
… but certainly weasel-worded to death, thus effectively erasing any competition to recent (i.e. post 1990) “unprecedented” weather. The “body English” on this carefully crafted sentence is plain to see.
“The EIV reconstructions suggest that temperatures were relatively warm (comparable with the mean over the 1961–1990 reference period but below the levels of the past decade)”
😐

tree ring series are screened for correlation with the actual temperature record, and series that don’t match up on a short term are simply excluded.
===========
The divergence problem is the result of faulty mathematics by climate scientists.
As soon as you, the climate scientists, use the results to “calibrate” (select) trees, it is the climate scientists (not climate) that is determining the tree rings statistically. This causes the trees to diverge from actual climate outside of the calibration period, because it is no longer climate that is determining the tree rings.
Using the “results” to determine the trees to include in a sample is statistically forbidden. Formally it is known as “selection on the dependent variable”. What this means is that any trees that have been “calibrated” cannot be trusted as a proxy for climate. Which includes just about every tree used by climate science over the past 20 years.
What you have is pseudo science that results from a faulty application of statistics.

P. Solar

Mike M says:
July 5, 2012 at 4:06 am
“The tree ring data suggest dry conditions during the Medieval Climate Anomaly summers, while the isotope data suggests wetter than expected winters.”
Isn’t that sort of a way to say that the two agree with each other but make it sound as though they don’t?
No, it’s a way of saying they don’t agree, but maybe we dont need to acknowledge that tree-rings are totally mixed up as proxies and should only be used for ring counting dendrochronology for C14 calibration.
Note the comment about they’re betting for spring and summer… also note the total absence of their sensitivity to CO2 levels.
What they are finally recognising in and backhanded and opaque way is that tree rings are no bloody use as long term temperature proxies. In fact, long term anything.

Bill Illis

For those double-checking Mann’s mathematical contortions, he archived the data and code for several of his papers at the NCDC paleo archive during June, 2012 (only 14 years late in some cases).
Just look for MannXXXX in this directory.
ftp://ftp.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/
I don’t see a “Steinman 2012” however.

jayhd

I remember seeing some old maps of America dating from the early eighteen hundreds. Several of those maps labeled the area east of the Rockies and west of the Mississippi as “the Great American Desert”. I’ve also read the Lewis and Clark papers, which also describe the aridness of the territory away from the immediate vicinity of the rivers. So aridity is hardly something new to the West and Northwest. And since the rivers of the Mississippi’s western drainage area do have water in them most of the time for the entire Summer and Fall, it stands to reason that the bulk of precipitation occurs during the late Fall, Winter and early Spring. Therefore it stands to reason the same cycles probably took place in the Medieval Warm Period. So what was the purpose of this paper?
Jay Davis

DesertYote

Oh for crying out loud! I grew up in the south west. My main interest was desert aquatic habitat. Decades ago, before the Marxist go around to rewriting the history, it was generally understood that the great droughts happened during periods of global cooling but the warm periods brought rain, like that which wiped out the Sonoran Indians’ irrigation systems!

Mike M

Yeah, using ‘MCA’ instead of ‘MWP’ scrubs away the nature of what happened no different than their lame switch from ‘global warming’ to ‘climate change’. Next they’ll change ‘LIA’ to PMCA – Post Medieval Climate Anomaly. (Is it just me or are they calling everything that’s natural an ‘anomaly’?)

MarkW

If lake levels drop enough, lake outflows can cease if the lake level drops below the outflow point.

Paul Coppin

Can’t see the whole paper, but on the surface, here we go again…
By comparing the two lakes, the researchers could determine the water balance between evaporation and precipitation.
Um, no. They could estimate a “water balance” between evaporation and precipitation of two specific lakes. Does sample size and variable parity not mean anything to “climate” scientists? (that, btw, is a rhetorical question). To his credit, the lead acknowledges a weakness in this regard.
Growth rings on trees are not only correlated with temperature and water. Rings of some trees may be, but sample size is critical for any ring proxy, with the possible exception of dendrochronology, which is temperature and moisture independent (mostly – even here there can be exceptions). The study has not been done that boxes the question about statistical robustness of sampling trees for growth based on free environmental variables.
We are looking again at grad student research supervised by a cohort of questionable supervisors. This isn’t to take away from the possibility that the research is decent, but, my tree ring and tea leaf proxies suggest the positive correlation is exceedlingly low.

Paul Coppin

Re “anomaly” – meant to include this in previous post. This constant insistence on the use of the word “anomaly” by Mann et all is (other than an affectation) apparently premised on the belief that climate soldiers on in fixed lockstep with a very narrow range of variables,viz. the GHGs, especially CO2, and that the relationship is linear, simple and persistent. You could argue that that assumption is the real anomaly.

TomRude

“We generally understand that the Medieval Climate Anomaly, a warm period in much of the northern hemisphere that occurred about 950 to 1250 was a dry period in the American West,” said Byron A. Steinman, postdoctoral researcher in meteorology, Penn State. “But there is complexity to the patterns of drought and it may not have been dry in winter in the Pacific Northwest.”
===
Is this fellow in meteorology or what? Since when a warm period means dry everywhere? Post modern meteo is truly pathetic.

dp

The area around Castor Lake is very contorted with lots of pot hole lakes. It was buried under the Okanogan tongue of the Cordilleran glacier and there is a lot of evidence of ice age dynamics all around the area. Our state is far enough north to have very long daytimes and we get lots of sunshine from the northeast and northwest during the summer months, and that part of the state is in the rain shadow of the Cascade range. Jet streams are a major weather driver. Not an easy place to understand without spending a lot of time there.

@Mike M.

Yeah, using ‘MCA’ instead of ‘MWP’ scrubs away the nature of what happened no different than their lame switch from ‘global warming’ to ‘climate change’. Next they’ll change ‘LIA’ to PMCA – Post Medieval Climate Anomaly. (Is it just me or are they calling everything that’s natural an ‘anomaly’?)

In ordinary usage, the term ‘anomaly’ denotes a event that is very strange or very unexpected. But in meteorology and climatology it has a more specialized mathematical meaning, denoting a signed deviation from a trend or norm:
http://www.ncdc.noaa.gov/cmb-faq/anomalies.php
This usage is justified because it is relatively hard to make two thermometers agree exactly on absolute temperature values, because of baseline calibration issues. But they will more often agree on relative changes in temperature. So, while they might differ by a degree or so on some absolute reading, they will be more likely to agree on a temperature increase or decrease of 1 degree.
This is especially true for temperatures derived from ‘proxies’ like tree rings or ice cores. Changes in temperature are more accurately discerned than baseline values.
Actually, _all_ thermometers depend on a proxy of some sort. e.g. expansion of a liquid or metal element, electrical current flowing through a thermocouple, detection of IR spectral components etc. All of these kinds of devices rely on the thermal behavior of some substance or process, thus are subject to errors of calibration and observation. There is no such thing as a thermometer that read temperature “directly”, without relying on some kind of “physics model”.
Having said that it should be noted that:
1) some thermometers are much more accurate than others
2) defining “MCA” as an “anomaly” that extends over 300 years is, IMO, an “anomaly” (in the ordinary sense of the word). Especially when these same folks who defined MCA insist that a recent decade or two is “climate”.
😐

LarryT

I hate to say this about my home state university and one of it leading professors. Any climate change claims coming out of Penn State or with an association to Mann must be accepted with a not believed until verified state of mind

u.k. (us)

Nice lead-in, Anthony.

Downdraft

Nick Stokes inserted a quote from a Mann study
“Hardly erased. Mann’s 2008 PNAS paper says, for example:
“The EIV reconstructions suggest that temperatures were relatively warm (comparable with the mean over the 1961–1990 reference period but below the levels of the past decade) from A.D. 1000 through the early 15th century, then fell abruptly. By contrast, the CPS reconstructions indicate more uniformly colder conditions, with peak Medieval warmth that does not breach the mean warmth of modern reference period (1961–1990), and a long-term, more steady decline in temperatures before 20th century warming.””
This raises the question of accuracy of short time scale responses in the referenced studies. Is it possible to differentiate a relatively short, 10 year period from the record? I am doubtful that the analysis is that fine on a decadal timescale. My point is, can Mann claim that the current warm period is warmer than the MWP based on the referenced analysis, or is he overreaching a bit?

stephen richards

When will these idiots come to understand that tree rings are not a proxy for anything but time.

ChE

“We generally understand that the Medieval Climate Anomaly, a warm period in much of the northern hemisphere that occurred about 950 to 1250 was a dry period in the American West,” said Byron A. Steinman, postdoctoral researcher in meteorology, Penn State. “But there is complexity to the patterns of drought and it may not have been dry in winter in the Pacific Northwest.”

No shirt, Shylock. Ever talked to anybody who lives there?

francois

Could we please have dates for the “medieval warm period-climate anomaly”, whatever you call it alongwith a rough idea of the affected area?

Tim Clark

I agree with DesertYote:
The importance concepts of this paper, glossed over by the warmista are:
Warm is wetter, Cold is drier.
In what conditions do plants grow better?

Keith Battye

You are taking the piss, surely.

Evidence supporting the existence of climate change is pummeling the United States this summer, from the mountain wildfires of Colorado to the recent “derecho” storm that left at least 23 dead and 1.4 million people without power from Illinois to Virginia. The phrase “extreme weather” flashes across television screens from coast to coast, but its connection to climate change is consistently ignored, if not outright mocked. If our news media, including—or especially—the meteorologists, continue to ignore the essential link between extreme weather and climate change, then we as a nation, the greatest per capita polluters on the planet, may not act in time to avert even greater catastrophe.
More than 2,000 heat records were broken last week around the U.S. The National Oceanic and Atmospheric Administration (NOAA), the government agency that tracks the data, reported that the spring of 2012 “marked the largest temperature departure from average of any season on record for the contiguous United States.” These record temperatures in May, NOAA says, “have been so dramatically different that they establish a new ‘neighborhood’ apart from the historical year-to-date temperatures.”

In the olden days it was called Medieval Climate Optimum. Is there a scientific justification for inventing new terms for an established concept?
With the same effort we could rename all the elements of the periodic table. That would be fun, would not it?
Could start with Nefarium (Atomic number: 6, Atomic weight: 12.0108).

Johanus

David Brown says:

If our news media, including—or especially—the meteorologists, continue to ignore the essential link between extreme weather and climate change, then we as a nation, the greatest per capita polluters on the planet, may not act in time to avert even greater catastrophe

So you blame the media for “ignoring the link”? Really? Hasn’t the news has been totally saturated lately with ‘extreme’ temperatures, wind, fire, and you-name-it?
Why do you look for MSM leadership in this matter?
What about your government leadership in Washington? Should not President O’Blamo take some ‘heat’ for this too? If this situation is really leading to a “catastrophe” (as you claim), then it shouldn’t take a lot of courage to take a stand on this, against a “catastrophe”, duh.
Then why is the President silent on this matter?
Maybe he’s trying to figure out a way to blame it on Bush. Or is it the case that he and his advisors know that whining about this particular “impending catastrophe” will not get him re-elected?
So which is more important: saving the world or re-electing O’Blamo?
(And China is the world’s worst polluter, not the U.S.)

Duster

“Medieval Climate Anomaly” has been around for some time (since the early ’90s at least). Other phrases for the same period include the Medieval Drought and the Medieval Climate Optimum. The preference tends to be geographically varying and appears to be influenced by where the user lived. In California it was referred to as a drought, sometimes the “Medieval Drought.” Effects in the Sierra were fairly catastrophic with prolonged periods during which mountain streams on the east side did not flow and Lake Tahoe did not discharge. The problem is that there is a four-fold set of relative states climate can move into: “warmer/drier”, “warmer/wetter”, “cooler/drier: and “cooler/wetter”. About the only “proxies” that really help differentiate those four contingencies are actual plant distributions. Stable isotope ratios that are tied to temperature won’t tell anything about precipitation intensities. In Oregon dramatic east/west movements of the sagebrush-pinyon paired with the yellow-pine-Douglas fir zones are visible in the pollen record, which probably reflect rain fall rather than temperature. These movements are also probably not sensitive at less that multicentury scales, since forests and brush lands can’t migrate like animal herds.

In ordinary usage, the term ‘anomaly’ denotes a event that is very strange or very unexpected.
And implicitly, something we can’t explain.
Like others, I haven’t read the paper (paywwalled), but they found 2 proxies that didn’t agree. The rest is speculation.
Until I see properly controlled greenhouse experiments that determine the variables that govern tree ring growth, I consider tree rings to be a proxy for something(s), but we don’t know what.

Konrad

“…MWP set to off. MCA repeater set to squawk mode B. O18 unit set to scramble. Both hands flapping, wrist strain nominal. Ready of takeoff on runway AR5. Remember people, keep a sharp lookout around Law Dome. That’s where the last crew bought the farm. The Grey Baron may be in the area…”

Konrad,
Funny and clever. I like it!

there is no evidence to suggest that the MWP was warmer than today. it was also a ”natural” warming period. todays warming is not. also the MWP was purely a northern hemisphere event . it was not global.

Johanus, the heat wave has been in the media but the reasons for it are ignored. and America is a bigger polluter than China ”per head of population”. i agree with you Obama is no better than Bush. [ in all areas, especially foreign policy ] lets face it both are and were appalling specimens. and Romney is just as bad

@Philip Bradley
> And implicitly, something we can’t explain.
In the ordinary sense of ‘anomaly’, perhaps.
But I think you’re overlooking the specialized, strictly mathematical sense of the word (as it used in meteorology and climatology):
http://mel.xmu.edu.cn/group/carbon/kcjs/Environmental_Oceanography/glossary/Anomaly.html
In this second sense of the word, it denotes anychange from a norm or trend, even very tiny ones. And they don’t have to be unusual or unexpected changes, just different than the trend.
Now the definition and calculation of the baseline trend or norm (from which anomalies are measured) is another matter, and always needs to be verified for soundness and accuracy.

tim clarke. warmer is wetter in some areas. increased heat means increased evaporation. in dryer areas increased heat can mean increased drought. however what is the situation globally, seeing that you are talking regionally? plant growth is dependent on a number of things, wetter may mean flood which is no good for growth. drought is obviously no good for growth, weeds and toxic plants can also thrive in the right conditions. not preferable. bigger plants also need more nutrition and more water. not going to happen in a drought

timetochooseagain

Philip Bradley says: “I consider tree rings to be a proxy for something(s), but we don’t know what.”
Presumably favorable conditions for tree growth (or not). Which would involve non linear combinations of a large number of factors two of which are climate variables we may be interested in (rain and warmth) but which is most important when is unknown. But what we can say for certain when a bunch of trees show enhanced growth: something (or everything!) was going good for them. And the reverse when they all show diminished growth.

Duster

david brown says:
July 5, 2012 at 5:20 pm
there is no evidence to suggest that the MWP was warmer than today. it was also a ”natural” warming period. todays warming is not. also the MWP was purely a northern hemisphere event . it was not global.

Please support this with something beyond blind assertions. Historical evidence shows the idea that the MWP was not warmer than the present is wrong on the face of it, on the basis of Greenland and England histories alone, or are you splitting hairs to say that today the northern hemisphere atleast has finally warmed back to historic levels? Also, the MWP period appears in the Antarctic stable isotope record suggesting that the event was global or had global atmospheric effects – whether it was actually warmer everywhere or not. As regards “today’s warming” in what way is it different than yesterday’s? There are no “unprecedented” rates of warming, no unprecedented warmth, the fires in Colorado are not unprecedented (look up Ranger Edward Pulaski). There is also every reason to anticpate that forest fires will in fact be worse for a long time – at least until the excesses of the “only you can prevent forest fires” attitude is gone. Major fires are a product of weather, fuel, and ignition sources. Importantly fuel has been increasing in national forests and other public and private lands for decades as a consequence of fire management practice that grew out of policy responses to major fires in the early 20th C. It has almost nothing at all to do with climate, though dry thunderstorms can provide ignition points – but thunderstorms are just weather, right?