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 air circulation systems clearly move cyclically poleward then equatorward then back again in both hemispheres in response to the battle between top down solar forcing and bottom up oceanic forcing. In that process the degree of meridionality shown by the jet streams alters total cloudiness and global albedo.
All global climate change is a consequence of those movements.
It’s just too obvious and too simple for anyone to accept.
Izen May 23, 2011 at 11:51 am
“Comparisons with selected temperature proxies from the Northern and Southern Hemispheres confirm that the MWP was highly variable in time and space. ”
Or temp proxies are only approximately dated or even invalid. They wouldn’t be the first proxies that have come to grief (to wit: those of the hockey stick). Also, note that comparisons here were made with selected temp proxies.
The main support for the MWP and the LIA comes from historical documentation, not proxies – proxies followed and can be said to have been somewhat validated by the prior knowledge. Unfortunately this means that only those parts of the globe where cultures kept records have been highlighted ( nevertheless, North America, Greenland, Europe, Asia is a hell of a piece of territory to have experienced it all by itself for a couple of centuries). Speaking of the downside of “fuzzy MWP” in time and space, this “regional” kind of climate thinking has a downside for CAGW, too. If you are comfortable with MWP being a patch on the globe, then how can you argue so strongly that CAGW wouldn’t also be a patch in roughly the same place – they are approximately similar in temp. The wrongful thinking isn’t dissimilar to the idea that ice found in the Arctic first wouldn’t cause one to expect it to be found in Antarctica.
izen: thank you and I agree with your final paragraph. That is, indeed, the question that matters.
izen says:
May 23, 2011 at 12:20 pm
Perhaps you would care to define ‘exceptional’ with special reference to the current UK weather.
Step one in reconstructing the MWP climate via one S.American lake.
Lots of other lakebed sediments to check out.
So, Mike, what caused the MWP, then?
(And were they able to grow more or less crops during that time?)
Izen says:
“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.”
More warmth has historically been very beneficial for civilization. Global cooling has been the real problem. A decade is a short trend, but it is still worrying.
izen says:
The peak had already passed and the Vikings in Greenland were begining to suffer the effects of a cooling climate by this date [1040]….
….and again:
The MWP clearly peaks at different times, it was just about over in Greenland by 1000AD
—————————————
The Greenlanders don’t see it that way:
http://www.greenland-guide.gl/leif2000/history.htm
But of course data derived from proxies etc. always trump historical accounts because they carry that invisible aura of ‘science’.
So temperature records follow solar output over thousands of years. This should put an end to the argument about solar forcing. At lower resolutions the influence of the PDO would also be important but is still linked to solar output. While the MWP and LIA are confirmed globally there is a likelihood that the northern hemisphere sees bigger shifts due to the topographic profile in the north, which affects jetstreams to a greater degree.
Speaking of the Mann Hockey Stick graph:
…….Even less confidence can be placed in the original conclusions by Mann et al. (1999) that “the 1990s are likely the warmest decade, and 1998 the warmest year, in at least a millennium”……
-National Academy of Science
-report on the Mann Hockey Stick graph, page 4
http://www.nap.edu/openbook.php?record_id=11676&page=4
Gates says:
“Of particular interest to me has been the Bond events…”
Then you may like this chart.
# # #
Also, since the temporal variations in the MWP in different regions is still being discussed here, it’s worth repeating Dr Loehle’s comment regarding the MWP:
“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.”
I trust Lohle’s statement puts that question to rest. What matters is whether the MWP and other warm Holocene optimums exceeded current temperatures. The physical evidence shows that they did [and the reaction to the MWP by the “Team’s” Jonathan Overpeck is about as unscientific as anyone can get: “We’ve got to get rid of the Medieval Warm Period!”].
But at least Overpeck’s motivation to protect his gravy train is clear [so is his willingness to doctor the climate record]. If the public realizes that the current gentle warming cycle has happened repeatedly in the past, they will see that there is no adequate reason to assign the blame to a tiny trace gas – unless there is empirical evidence. But there is no evidence, none at all. The demonization of “carbon” is based on GCMs; computer climate models, which are even less accurate than economic models. And of course if econ models were accurate, their programmers and owners would be as rich as Croesus.
Scottish Sceptic writes,
“Gotcha Mann!
Now tell us that the medieval warm period was just a small regional effect.”
Smokey writes,
“Note that this is empirical evidence, not George Orwell-type language games or Michael Mann’s cherry-picked and debunked treemometer proxies.”
Smokey writes,
“Mann tried to erase the MWP [the long shaft of his Hockey Stick] and was debunked.”
Amino Acids in Meteorites writes,
“Speaking of the Mann Hockey Stick graph”
Since we’re speaking of Mann … look again at that colorful graphic, Fig. 5 from the article, that Anthony reproduces above. The second plot in Fig. 5 compares the authors’ Pumacocha reconstruction (gray) alongside the Northern Hemisphere temperature reconstruction of Moberg et al (2005). The fourth plot compares it with another well accepted reconstruction, North Atlantic sea surface temperatures from Mann et al (2009), which like many other studies (including Moberg and this one) report geographically widespread evidence of the Medieval Climate Anomaly and Little Ice Age.
“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.”
I don’t think this accurately characterises mainstream understanding. The MWP and LIA are not in doubt regarding their existence. The dispute is about whether the global temperature was higher durig the MWP than now, and the mainstream response is that while the globe was warm, the effects were not uniform temporally and spatially, indicating that current temps are higher. There are plenty of studies of different parts of the world that demonstrate this lack of uniformity, but the ensemble of these does point to a warm medieval period and a cold LIA.
IOW, Anthony’s right about the regional effects, but wrong to suggest that this has been used to deny the existence of the MWP.
The full version of the paper is online:
http://www.pitt.edu/~mabbott1/climate/mark/Abstracts/Pubs/Birdetal11PNAS.pdf
Reading through the comments and keeping in mind the issue at stake, these excerpts sprang out of the paper.
Smokey says:
May 23, 2011 at 6:15 pm
Gates says:
“Of particular interest to me has been the Bond events…”
Then you may like this chart.
______
Very interesting chart. Made even more so by the association of these events with longer term solar cycles and GCR variations. Thanks…
It’s encouraging to note that followers of ‘IPCC science’ have reluctantly accepted the existence of the MWP, although comically, as yet, they cannot allow themselves to use that label, preferring Medieval Climate Anomaly (MCA) instead.
But the period c.900-c.1300 was not anomalous (climate-wise) within the Holocene so far.
It was the period c.1400-c.1800 which was anomalous in that it was about the coldest since the Younger Dryas.
http://muller.lbl.gov/pages/iceagebook/history_of_climate.html (Muller).
Smokey says:
May 23, 2011 at 11:33 am
“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”:”
There’s a wonderful irony here. On the one hand, the Team is using this ‘trick’ question and fixating on any deviations from THEIR monolithic MWP… if it didn’t simultaneously warm up everywhere, it must be CO2, or something like that.
On the other hand, now when things are highly variable across the planet it is a sure sign of the Planetary Fever.
Was there no warmcold in the MWP?
KnR says:
Of course the claim was that MWP was regional , but you notice no one side how big the region was just it was one . So as long as you can’t prove that the MWP existed in ever square cm of the planet , its ‘regional’ no matter how big the region . Climate science 101.
On the other hand anything detected by “climate scientists” must be “global”. No matter how small a part of the planet it actually applies to 🙂
FYI – Every paleo type study I have seen in New Zealand also confirms a MWP and LIA, so it definitely was not confined to the northern hemisphere. That includes species distribution (for example Totara remains are found further south than the current distribution), stalagmite records, Maori history, records of glacier recession / growth etc… it all supports it.
The Ministry for the Environment even published a “best estimate” record in a 2004 climate change report that clearly documented it plus further past warm episodes. (they omit the graph in the reports since though – made the current climate look cooler than normal – wasn’t a good look for the warmist brigade!)
Good to see further studies confirming a SH LIA and MWP – maybe Mann being an impartial scientist should update his prior studies to include all these SH proxies with a MWP?
Let me agree with you for just 1 minute. Now do you also agree that the Minoan and Roman warm periods were also exceptional?
http://climate.geologist-1011.net/HoloceneTemperatures.png
@- Jimbo says:
May 24, 2011 at 3:04 am
“Let me agree with you for just 1 minute. Now do you also agree that the Minoan and Roman warm periods were also exceptional?”
No, as I mentioned on the issue of ‘exceptionality’ before it depends on context.
I would accept that proxy records of past temperature are not sufficiently accurate or global to define the present climate as exceptional in relation to the MCA or LIA or any of the other past putative warmings except perhaps the Holocewne maximum after the big thaw ~8000 years ago.
What puts present conditions into the exceptional class is the concurrent sea level rise and ice-mass loss which is unprecendented since the Holocene maximum. The usual pattern of interglacial periods in past ice-ages has had a maximum immediately after the big melt and then falling temperatures for the next few thousand years. Temperatures and a LOSS of ice mass 10,000 years AFTER the post-melt maximum is exceptional.
izen says::
“Holocewne maximum after the big thaw ~8000 years ago.”
That’s not the “maximum”.
“The usual pattern of interglacial periods in past ice-ages has had a maximum immediately after the big melt and then falling temperatures for the next few thousand years. Temperatures and a LOSS of ice mass 10,000 years AFTER the post-melt maximum is exceptional.”
You can’t know that. Nobody knows exactly how long it took between the peaks (warm period-no ice) and troughs (cold period-ice) in the Milanknovitch Cycles. The data resolution isn’t good enough. You can only approximate. The data resolution is plus or minus thousands of years or more. The f[ur]ther you go back in time the margin for error gets even larger.
The last big interglacial period ~125,000 yrs ago, which geologists know quite a lot about; sea level high stands were 15-20 ft higher then today. We are no where near that right now.
http://www.ncdc.noaa.gov/paleo/globalwarming/paleobefore.html
@- liza says:
May 24, 2011 at 6:22 am
“The last big interglacial period ~125,000 yrs ago, which geologists know quite a lot about; sea level high stands were 15-20 ft higher then today. We are no where near that right now.”
But we are getting closer.
The conditions during the peak of the Eemian were only a few degrees more than present, and if projections of the likely physical effect of the increased CO2 are close to correct that temperature will be reached in the next century.
Then as the past shows the sea level rise will be likely to reach ~20 ft higher than the present.
There may also be arid deserts over large inland areas of the continents.
“The conditions during the peak of the Eemian were only a few degrees more than present, and if projections of the likely physical effect of the increased CO2 are close to correct that temperature will be reached in the next century.
Then as the past shows the sea level rise will be likely to reach ~20 ft higher than the present.
There may also be arid deserts over large inland areas of the continents.”
Wow. That sounds just like Algore.
Unfortunately for the believers in CO2=CAGW, the planet isn’t cooperating.
Izen says
“The usual pattern of interglacial periods in past ice-ages has had a maximum immediately after the big melt and then falling temperatures for the next few thousand years. Temperatures and a LOSS of ice mass 10,000 years AFTER the post-melt maximum is exceptional.”
Not really, the last (Eemian, MIS 5e) interglacial for example was double-peaked with a cool episode with significant ice accumulation (lower sea levels) in between. The one before that (MIS 7) had three marked peaks (MIS 7.1, 7.3 and 7.5). It is true that the first interglacial peak is usually the warmest, but that is true of the current one too (we are a long way from the climatic optimum at the moment)
Also claiming that the MWP had peaked by 1040 in Greenland is very doubtful. Climate there was warmer than at present (with grain growing marginally possible) as late as the thirteenth century (ref. Kónungs Skuggsjá). In Iceland where historical data are very good the main temperature decline (and the end of grain production) came in the fifteenth century.
By the way it is interesting to note that while the last (Eemian) interglacial, which was a lot warmer than the present one, was also wetter than the present almost throughout the tropics. Just about the only exception was the Andean altiplano which was hyperarid.
Also the usual claims about 20-30 feet higher sea levels during the last interglacial are very shaky. They are based on just a few sites of often questionable tectonic stability (like Hawaii and Bermuda). The best data from the very stable Australian craton indicates that 10 feet is a more likely figure .