This study from the University of Pittsburgh and SUNY-Albany set out to illustrate how rainfall patterns changes with global temperature in South America. They found the link they were looking for. At the same time, they validated the existence of the Medeival Warm Period and the Little Ice Age effects in the Southern hemisphere, which is interesting since many claim the effects were regional, not global. See the image at left and press release below.
Pitt-led Team Unearths 2,300-Year Climate Record Suggesting Severe Tropical Droughts as Northern Temperatures Rise
A sediment core from a South American lake revealed a steady, sharp drop in crucial monsoon rainfall since 1900, leading to the driest conditions in 1,000 years as of 2007 and threatening tropical populations with water shortages, a team from Pitt, Union College, and SUNY-Albany reports in PNAS
PITTSBURGH—A 2,300-year climate record University of Pittsburgh researchers recovered from an Andes Mountains lake reveals that as temperatures in the Northern Hemisphere rise, the planet’s densely populated tropical regions will most likely experience severe water shortages as the crucial summer monsoons become drier. The Pitt team found that equatorial regions of South America already are receiving less rainfall than at any point in the past millennium.Laguna Pumacocha in the Peruvian Andes.
The researchers report in the Proceedings of the National Academy of Sciences (PNAS) that a nearly 6-foot-long sediment core from Laguna Pumacocha in Peru contains the most detailed geochemical record of tropical climate fluctuations yet uncovered. The core shows pronounced dry and wet phases of the South American summer monsoons and corresponds with existing geological data of precipitation changes in the surrounding regions.
Paired with these sources, the sediment record illustrated that rainfall during the South American summer monsoon has dropped sharply since 1900—exhibiting the greatest shift in precipitation since around 300 BCE—while the Northern Hemisphere has experienced warmer temperatures.
Study coauthor Mark Abbott, a professor of geology and planetary science in Pitt’s School of Arts and Sciences who also codesigned the project, said that he and his colleagues did not anticipate the rapid decrease in 20th-century rainfall that they observed. Abbott worked with lead author and recent Pitt graduate Broxton Bird; Don Rodbell, study codesigner and a geology professor at Union College in Schenectady, N.Y.; recent Pitt graduate Nathan Stansell; Pitt professor of geology and planetary science Mike Rosenmeier; and Mathias Vuille, a professor of atmospheric and environmental science at the State University of New York at Albany. Both Bird and Stansell received their PhD degrees in geology from Pitt in 2009.
“This model suggests that tropical regions are dry to a point we would not have predicted,” Abbott said. “If the monsoons that are so critical to the water supply in tropical areas continue to diminish at this pace, it will have devastating implications for the water resources of a huge swath of the planet.”
The study compared the record in the Pumacocha sediment core (PC) to various geological records from South America—Cascayunga Cave (CC), the Quelccaya ice Cap (QIC), and the Cariaco Basin (CB)—as well as the annual position of the Intertropical Convergence Zone (ITCZ).
The sediment core shows regular fluctuations in rainfall from 300 BCE to 900 CE, with notably heavy precipitation around 550. Beginning in 900, however, a severe drought set in for the next three centuries, with the driest period falling between 1000 and 1040. This period correlates with the well-known demise of regional Native American populations, Abbott explained, including the Tiwanaku and Wari that inhabited present-day Boliva, Chile, and Peru.
After 1300, monsoons increasingly drenched the South American tropics. The wettest period of the past 2,300 years lasted from roughly 1500 to the 1750s during the time span known as the Little Ice Age, a period of cooler global temperatures. Around 1820, a dry cycle crept in briefly, but quickly gave way to a wet phase before the rain began waning again in 1900. By July 2007, when the sediment core was collected, there had been a steep, steady increase in dry conditions to a high point not surpassed since 1000.
To create a climate record from the sediment core, the team analyzed the ratio of the oxygen isotope delta-O-18 in each annual layer of lake-bed mud. This ratio has a negative relationship with rainfall: Levels of delta-O-18 are low during the wetter seasons and high when monsoon rain is light. The team found that the rainfall history suggested by the lake core matched that established by delta-O-18 analyses from Cascayunga Cave in the Peruvian lowlands and the Quelccaya Ice Cap located high in the Andes. The Pumacocha core followed the climatological narrative of these sources between the years 980 and 2006, but provided much more detail, Abbott said.
The team then established a connection between rainfall and Northern Hemisphere temperatures by comparing their core to the movement of the Intertropical Convergence Zone (ITCZ), a balmy strip of thunderstorms near the equator where winds from the Northern and Southern Hemispheres meet. Abbott and his colleagues concluded that warm Northern temperatures such as those currently recorded lure the ITCZ—the main source of monsoons—north and ultimately reduce the rainfall on which tropical areas rely.
The historical presence of the ITCZ has been gauged by measuring the titanium concentrations of sea sediment, according to the PNAS report. High levels of titanium in the Cariaco Basin north of Venezuela show that the ITCZ lingered in the upper climes at the same time the South American monsoon was at its driest, between 900 and 1100. On the other hand, the wettest period at Pumacocha—between 1400 and 1820, which coincided with the Little Ice Age—correlates with the ITCZ’s sojourn to far south of the equator as Northern Hemisphere temperatures cooled.
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Levels of the oxygen isotope delta-O-18 from Pumacocha overlaid with corresponding levels from Cascayunga Cave (red) and Quelccaya Ice Cap (blue).h/t to reader Dennis via emailDiscover more from Watts Up With That?
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The research looked at proxy measures of rainfall, NOT temperature. The assumption is, from other research, that the change in rainfall corellates with temperature changes.
That a Medieval climate anomaly exists is not in dispute. The controvesry arises over its magnitude and timing globaly. This reseach seems to show that the MWP was not as pronounced a warming in the S.H. as in in Northern latitudes, and with a peak around 1040 is later than the peak in the Northern hemisphere. The peak had already passed and the Vikings in Greenland were begining to suffer the effects of a cooling climate by this date.
This research does seem to confirm that any MWP was not warmer, or at least dryer than the present; confirming that present conditions are exceptional.
“The Pitt team found that equatorial regions of South America already are receiving less rainfall than at any point in the past millennium.”
“they validated the existence of the Medeival Warm Period and the Little Ice Age effects in the Southern hemisphere”
———-
They did no such thing.
The Medieval Warm Period is a temperature anomaly. They don’t have a temperature-sensitive proxy, so they cannot, and did not try to reconstruct temperature. They have a precipitation proxy. To infer that the MWP of the North Atlantic region had far-field impact is a fair interpretation. To conclude that the MCA was a globally warm phase is to make the same fundamental mistake as Soon and Baliunas (2003).
REPLY: Well, you are entitled to your opinion, but so much rides on making the MWP go away, I choose to side with Soon and Baliunas (2003) over your opinion, which isn’t peer reviewed. See the upcoming article for more things being said about the hockey stick that I’m sure will bother you. – Anthony
Izen says:
“That a Medieval climate anomaly exists is not in dispute. The controvesry arises over its magnitude and timing globaly.”
There is no controversy. Let me correct your disingenuous little head: The MWP was a global event, as is verified by the strong corellation between both hemispheres.
Note that this is empirical evidence, not George Orwell-type language games or Michael Mann’s cherry-picked and debunked treemometer proxies. Did you actually think you would get away with trying to sell your ‘medieval warming anomaly’ bullshit here? Run along to Skeptical Pseudo-Science or RealClimatePropaganda, they like dishonest language corruption like that. But here at the internet’s Best Science site, honest terminology matters, and peddlers of junk science are called out.
Berényi Péter says:
May 23, 2011 at 6:53 am
“The Pitt team found that equatorial regions of South America already are receiving less rainfall than at any point in the past millennium”
The only problem with this proposition is that it’s not true. We have monthly average Heights of the Rio Negro river at Manaus from January 1903 to December 1992 in metres, relative to an arbitrary reference point for example.
It has a rising trend of 9.23 mm/annum.
Yeah, but that would be due to the rotten water. The good water has decreased and it’s worse than we thought. 😉
izen: logical fault. Even given your claims about the magnitude of the MWP the proposition that the peak temperature then was less than now does not confirm that the ‘present conditions are exceptional’. All it shows, if true, is that the warming in the modern era is greater than the most recent peak in global temperatures. However, my understanding of the uncertainties attaching to the proxy studies done so far is that they cannot resolve temperatures around 1000 AD to anywhere near the accuracy your statement would require to be true.
Oh Smokey! I love it when you get smokin’ hot around the collar 🙂
Soon and Baliunas (2003) was of course peer-reviewed: four reviewers rejected it. It was only ever published because the editor sweet-hearted it in.
REPLY: Yes, it had those dangerous ideas that didn’t go with the consensus wot dun it. Climategate shows us how that rolled. BTW Richard, will you ever be able to bring yourself to making a positive contribution here? You do nothing but complain. – Anthony
Joe Lalonde says:
May 23, 2011 at 5:25 am
Anthony,
I love the way conclusions are made for little evidence support in a time frame that is extremely minor the time frame of the whole planet.
Joe, can you please rephrase the above sentence? Right now it makes no literal sense.
John Marshall says:
May 23, 2011 at 5:51 am
According to 971 scientists from 562 research institutions the MWP is a fact of history. This research covers 43 different countries, Northern and Southern hemispheres.
So the above report, important though it is, is not the first and doubtless not the last.
IPCC please note.
Hi John.
Thanks for the info, any chance of referencing it with links?
thanks.
Dave
richard telford says:
May 23, 2011 at 8:15 am
=================================
Richard, you’re a hoot.
The MWP was only in a suburb of Minneapolis…
…happy now
In spite of anything that has to do with sense, only certain parts of the planet got warmer, and had no effect on any other parts….
There’s an invisible wall that stops it.
…just like the GISS color coded temp maps
Why is there no data plotted for the Caricao Basin after about 1850? Are they attempting to “hide the decline?”
This would make sense if the rainfall has been increasing since the 1900s as Berényi Péter pointed out in his link.
“The only problem with this proposition is that it’s not true. We have monthly average Heights of the Rio Negro river at Manaus from January 1903 to December 1992 in metres, relative to an arbitrary reference point for example.”
“It has a rising trend of 9.23 mm/annum.”
Telford replied to my question about why he can’t ever seem to say anything positive and always complains, citing that I was “spreading hate” so it was not approved. Try again Richard.
There are lots of studies indicating the MWP was global in nature. See the Medieval Warm Period Project.
@- Smokey says:
May 23, 2011 at 8:44 am
“There is no controversy. Let me correct your disingenuous little head: The MWP was a global event, as is verified by the strong corellation between both hemispheres. ”
I agree it was global, just not synchronous between the hemispheres.
In the interests of using real data rather than ‘George Orwell-type language games or Michael Mann’s cherry-picked and debunked treemometer proxies,’ I was going to provide this link –
http://pages.science-skeptical.de/MWP/MedievalWarmPeriod.html
Which not only shows many of the proxy records from which you can detect a medieval climate anomaly, but also shows the differences in timing between different regions of the peak of the event.
Then I realised that you had already included the same link in your reply.
Have you not examined that graphic of map and data? You can spend some time playing a version of the ma-jong tile-matching game trying to find two records with matching peak times. Very difficult if they are in different hemispheres!
Perhaps you were not aware that the very data you linked to confirms my claim that the peak of any MWP was NOT globally synchronous.
I have no idea why you included the other link, it shows data from both polar ice-cores, but with a timescale of kiloyears so the MWP is indistinguishable in the mass of lines on the extreme final few left-hand mm of the graph. The peaks marked are around 80,000 and 110,000 years ago during the last ice-age. Presumably this was linked in error.
Perhaps you have some other evidence that refutes the research reported above that quite clearly states the detected rainfall changes associated with a southern hemisphere MWP peak after 1000AD.
-“But here at the internet’s Best Science site, honest terminology matters, and peddlers of junk science are called out.”
I would certainly hope so.
It would be depressing if people could link to data and make claims that were not bourne out by the data. Would you care to present any research that supports a simultaneous MWP or would you concede that as the link we BOTH favour shows it peaked at different times in different regions?
This should bring an end to the continued misconception that the MWP and LIA were regional-only events. It is undeniably clear they were not…
The MWP was global. Here are links to the relevant papers concerned.
http://sites.google.com/site/globalwarmingquestions/mwp
It was global!
Global:
Glacial geological evidence for the medieval warm period
Was the medieval warm period global?
Ljungqvist et al [pdf]
Reconstructing Climatic and Environmental Changes of the Past 1000 Years
Antarctica:
B.L. Hall et. al.
E. Castellano et. al.
B.L. Hall et. al.
Brenda L. Hall
Margaret B. Williams et. al.
Boo-Keun Khim et. al.
Southern South America:
Torsten Haberzettl et. al.
Dmitri Mauquoy et. al.
C.M.F Dubois – Universidad Nacional del Centro
Ricardo Villalba – University of Colorado
New Zealand:
P. W. Williams et. al.
Edward R. Cook et. al.
Izen,
Since you asked, here’s a chart with a much shorter time scale.
And I would be glad to discard MWP and MWA in favor of the Medieval Optimum since it was a global warming similar to the Holocene Optimum, the Minoan Optimum and the Roman Optimum – not as warm as those three preceding, but warmer than today.
The devious effort to downplay the MWP is so transparent to those who follow the issue that it is hard to conclude that it is anything but alarmist propaganda. See Jimbo’s link for refutation.
@-Berényi Péter says:
May 23, 2011 at 6:53 am
“The only problem with this proposition is that it’s not true. We have monthly average Heights of the Rio Negro river at Manaus from January 1903 to December 1992 in metres, relative to an arbitrary reference point for example.
It has a rising trend of 9.23 mm/annum.”
That would make the river around a metre higher than when first measured against the steps of the local building used as the datum point.
Are you sure that the only explanation for this rise is increased rainfall?
Could water extraction in the town/city of Manaus have caused any subsidence of the two datum points?
Or is river level also mediated by changes in the sediment deposition further down river at the confluence of the Negro and Amazon?
The question of whether the MWP happened simultaneously over the globe is simply an attempt to muddy the waters. The central issue is: ‘was the MWP global?’ – not: ‘did the MWP begin and end at the same time everywhere?’ Avoiding the main issue is just misdirection [AKA: “Look over there! A kitten!]
Dr Craig Loehle explains that the MWP was not simultaneous over the globe. He refers to it as “time transgressive”:
“A good example is the warming at the last glacial termination. Because the ice sheets took so long to melt, the warming took longer to reach eastern Canada which still had ice. Thus a peak in warming moved across the northern regions, and individual records of climate will not agree on the date of the warming. To say this applies to the Holocene Optimum at 8,000 to 6,000 BP is not a documented result, and to say it applies to the MWP is without foundation at all, but is a ‘clever way to deal with a problem’ (that, and claiming it was only Europe that got warm at the MWP).”
The alarmists’ consternation with the MWP is simply that it occurred prior to the industrial revolution. Mann tried to erase the MWP [the long shaft of his Hockey Stick] and was debunked. With a MWP, the current mild warming of only 0.7°C over a century and a half is unremarkable, and no different from past natural variability. Blaming CO2 is just a convenient way to tax all things “carbon”.
Here is South Africa’s MWP.
@-Smokey says:
May 23, 2011 at 11:13 am
“Since you asked, here’s a chart with a much shorter time scale.”
No it isn’t. It graphs the last ice-age going back 90,000 years with the present depicted in the last 10kyr division on the far left.
“…The devious effort to downplay the MWP is so transparent to those who follow the issue that it is hard to conclude that it is anything but alarmist propaganda. See Jimbo’s link for refutation.”
Is it ore devious than the effort to exaggerate the MWP which is so transparent to those who follow the issue that it is hard to conclude that it is anything but rejectionist propaganda.
I have followed the links provided by Jimbo, here are some quotes –
“Comparisons with selected temperature proxies from the Northern and Southern Hemispheres confirm that the MWP was highly variable in time and space. ”
“This proxy suggests that during the late Middle Ages (ca. AD 1230–1410) the lake level was rather low representing a signal of the ‘Medieval Climate Anomaly’ in southeastern Patagonia.”
“CH3Cl levels were elevated from 900–1300 AD by about 50 ppt relative to the previous 1000 years, coincident with the warm Medieval Climate Anomaly (MCA).”
The MWP clearly peaks at different times, it was just about over in Greenland by 1000AD but still rising in Patagonia. You can define the MWP as a vague, fuzzy period from 800AD to 1400AD which was global, but the timing of the peaks during those centuries was not globally synchronous. That makes it difficult to argue that it was an event with enough similarities to the present warming that IS globally synchronous and very difficult to maintain that the evidence shows it represents a similar gain in energy rather than the redistribution of energy between regions and hemispheres.
There is a final irony in all this. IF the MWP was of similar magnitude to present warming it would indicate that climate sensitivity is greater because so much warming came from rather small solar/volcanic variations. That has serious implications for the magnitude of present warming from the increased energy returned to the surface as DLR from increased CO2. Presumably a conclusion you would not want ?
Several hundred peer reviewed papers recording the MWP from proxy studies from every continent on earth, are listed at CO2 Science, by continent and each summarised in a mini-abstract:
http://www.co2science.org/data/mwp/mwpp.php
Our troll guests should feel free to refute each one of these in turn.
Don B says:
May 23, 2011 at 7:03 am
In Jasper Kirkby’s “Cosmic Rays and Climate,” on page 3 is a graph of Venezuelan Andes glacier growth and shrinkage for eleven hundred years.
http://aps.arxiv.org/PS_cache/arxiv/pdf/0804/0804.1938v1.pdf
The MWP and the LIA are obvious, as is the correlation with cosmic rays.
______
Thanks for this link. Of particular interest to me has been the Bond events (mentioned in the article you’ve referrenced). I’ve thought for quite some time that the MWP was global in nature based on my reading of the subject, and certainly involved changes in the ITCZ, but the excellent connections made in this this article between Solar Activity/GCR’s/Bond Events/ITCV etc was very useful. Thanks again…
@-Professor Bob Ryan says:
May 23, 2011 at 8:52 am
“izen: logical fault. Even given your claims about the magnitude of the MWP the proposition that the peak temperature then was less than now does not confirm that the ‘present conditions are exceptional’. ”
I agree, my apologies.
‘Exceptional’ requires some criteria of definition. The exceptional weather we are having at present in the UK would not be exceptional for mid-summer. It is necessary to define the context before a condition can be so labeled.
“However, my understanding of the uncertainties attaching to the proxy studies done so far is that they cannot resolve temperatures around 1000 AD to anywhere near the accuracy your statement would require to be true.”
Yes, The proxy studies of rainfall or temperature are ambiguous and I would accept that alone they lack the accuracy to definitively refute either hypothesis.
The present warming is certainly not exceptional over long timescales, the Holocene maximum around 8000yrs BPE seems to have been warmer, but ice-mass and sea level indicate nothing comparable since.
Modern industrial/technological civilisation got going during the LIA. The question of interest is how robust are such societies when the climate alters enough to disrupt agricultural systems. It may not require warming that could be described as exceptional over tens of kiloyears, but may be susceptible to variations, AGW or otherwise, of century scales.