Study: “Little Ice Age” also affected South American climate

Research shows how the Little Ice Age affected South American climate

For the first time, scientists reconstruct the rainfall distribution in Brazil during the climate changes that marked the Middle Ages using isotopic records from caves.

A new study published in Geophysical Research Journal shows that the so-called Little Ice Age – a period stretching from 1500 to 1850 in which mean temperatures in the northern hemisphere were considerably lower than at present – exerted effects on the climate of South America.

Based on an analysis of speleothems (cave formations) in the Brazilian states of Mato Grosso do Sul and Goiás, the study revealed that in the seventeenth and eighteenth centuries, the climate of southwestern Brazil was wetter than it is now, for example, while that of the country’s Northeast region was drier.

The same Brazilian cave records showed that the climate was drier in Brazil between 900 and 1100, during a period known as the Medieval Climate Anomaly (MCA), when the northern hemisphere’s climate was warmer than it is now.

The study’s authors are physicist Valdir Felipe Novello and geologist Francisco William Cruz, researchers at the University of São Paulo’s Geoscience Institute (IGC-USP), in collaboration with colleagues in Brazil, the United States and China. The study was part of the ongoing project “Climate research education in the Americas using tree-ring speleothem examples: PIRE-CREATE”, which was supported by the São Paulo Research Foundation (FAPESP) under an agreement with the US National Science Foundation (NSF) via NSF’s Partnerships for International Research and Education (PIRE) Program.

The study detected dry and wet periods in the Brazilian paleoclimate by analyzing the oxygen isotopes in calcium carbonate molecules found in speleothems. “In Professor Cruz’s group, we travel throughout Brazil collecting samples of cave rocks. The composition of oxygen isotopes in the calcium carbonate deposited over centuries and millennia to form speleothems [stalagmites and stalactites] shows whether the climate was drier or wetter in the past,” said Novelo.

Dry and wet season isotopes

Isotopes are variants of a chemical element. While all isotopes of any element have the same number of protons in each atom, different isotopes have different numbers of neutrons. For example, oxygen 16 (16O) has eight protons and eight neutrons, while oxygen 18 (18O) has eight protons and ten neutrons.

“In nature there is approximately one atom of oxygen 18 for every 1,000 atoms of oxygen 16,” Novello explained. 18O is heavier than 16O, so when it starts to rain, water molecules with 18O precipitate first.

As a result, the amount of 16O in the rain cloud rises relative to the amount of 18O, which necessarily decreases since most of the original 18O precipitates as rain. “When it rains heavily, the rain’s isotope profile changes,” Novello said.

To determine how changes in past rainfall regimes can be measured, Novello and Cruz analyzed records of the 16O/18O ratio preserved in speleothem calcium carbonate.

Caves form during long rainy periods in regions of karst, a type of landscape comprising carbonatic rocks such as limestone. Rainwater comes into contact with carbon gas (CO2) dissolved in the air and soil. The result of this chemical reaction is slightly acidic water, which penetrates the soil until it reaches underground calcareous rock.

Calcareous rock is insoluble in water with neutral pH but dissolves in the presence of acidic water (which has a moderately low pH), leading to the formation of the natural underground voids we call caves.

The researchers explained that speleothems form when calcium carbonate-loaded rainwater that has penetrated the soil reaches the cave’s roof. Slow continuous dripping over thousands of years precipitates the calcium carbonate dissolved in each drop in the form of speleothems, as stalactites suspended from the roof of the cave and as stalagmites rising from the floor.

Any calcium carbonate precipitating from the roof is deposited on the floor in layers that build up to form stalagmites. Speleothems preserve the isotope signature of the oxygen in the rain that fell at the time when each layer of calcium carbonate was deposited.

“So, in a region with heavy rainfall, for example, you tend to find speleothems with sequences of layers containing less 18O. Conversely, in regions with a dry climate, the small amount of rainfall contains more 18O. When this water penetrates the soil and dissolves calcium carbonate, it ends up creating speleothems with a relatively high level of 18O.”

Rock dating and isotope analysis

Novello collected rock samples from two stalagmites in Jaraguá Cave, near Bonito, Mato Grosso do Sul, and from stalagmites in São Bernardo Cave and São Mateus Cave, located in Terra Ronca State Park, Goiás.

Two samples from two different stalagmites were collected in Jaraguá Cave. One of them grew continuously for 800 years according to uranium-thorium dating, between 1190 and 2000, a period that included the LIA. The other sample grew continuously in 442-1451, a period that included the MCA.

In Goiás, Novello collected a rock sample from São Bernardo Cave which covered the period 1123-2010, which included the LIA. São Mateus Cave yielded sample dated to the period 264-1201, which included the MCA.

The FAPESP-supported study showed that the 18O profile of the samples from Jaraguá Cave displayed declining levels of oxygen in the period 400-1400, suggesting a moderately wet climate in central Brazil during the period (which included the MCA in the northern hemisphere).

Levels of 18O in the samples from Jaraguá Cave fell between 1400 and 1770, reflecting a rise in moisture during the period (which included the LIA in the northern hemisphere), but rose between 1770 and 1950, in line with falling moisture.

A similar analysis of the samples from São Bernardo Cave and São Mateus Cave in Goiás did not show any clear trend, but there were a number of long wet periods, mainly 680-780 and 1290-1350, with spikes in 1050, 1175 and 1490.

On the other hand, the wet period documented by the record from the Jaraguá Cave during the LIA in 1500-1850 is consistent with the wet conditions favored by passage of the South Atlantic Convergence Zone (SACZ), a large cloud system with a northwest-southeast orientation that extends from southern Amazonia to the central South Atlantic in the summer.

“The SACZ is the cloud mass responsible for the long periods of rain that occur in Brazil’s Southeast region. The isotopes tell the full story of this wet mass and its movement across the continent,” Novello said.

In a previous study using isotope records from caves in Brazil’s Northeast region (at Iraquara, Bahia), Novello had inferred that a drier climate prevailed during the LIA in that region, which is outside the SACZ.

“The data from speleothems in Bonito, associated with known paleoclimate data from Peru, show that during the LIA, the SACZ more frequently stalled further to the southwest over an area that extends from Peru to São Paulo via Mato Grosso do Sul,” he said. “On the other hand, the data from the caves in Goiás and Iraquara suggest the SACZ didn’t reach Goiás, Bahia and the Northeast during the LIA, but stayed put over the Southeast. As a result, the Northeast became drier.”

Although the records from the two caves in Goiás (and three other caves) showed no significant change in the average proportion of 18O during the periods that included the MCA and LIA, they did point to strong variability on a multidecadal to centennial timescale during the period of transition from the MCA to the LIA (1100-1500).

Convergence zones

“There’s coherence between climate changes in South America and the climate data for the northern hemisphere,” said Cruz, principal investigator for the FAPESP-funded project. “Earth’s climate is entirely interconnected. If there are anomalies in high-latitude regions, this will be reflected in the tropics.”

“When we look at the paleoclimate data for the period corresponding to the LIA, we see more cold in South America, but the rainfall patterns changed,” Novello said. From this information, it can be concluded that if the climate grows colder in the northern hemisphere, it rains more in the southern hemisphere. The moisture convergence ends up moving south. Conversely, when the climate warms up in the northern hemisphere, it rains less in the southern hemisphere.

“In the equatorial regions, there’s a belt of cloud called the Inter Tropical Convergence Zone. Its location corresponds to the area where the ocean surface is warmer. This warmer region creates a low-pressure zone to which all the moisture converges, and so more rain falls.”

During the LIA, when the difference between the cooler climate in the northern hemisphere and the warmer climate in the southern hemisphere was greater, the winds that converged from the northern hemisphere to the Inter Tropical Convergence Zone (ITCZ) carried more moisture than they do now. This greater moisture contributed to an increase in the volume of cloud in the ITCZ, which advanced east-west over the equator from the Atlantic to the Amazon, where it began raining torrentially. This was when all the 18O contained in the clouds precipitated.

“The cooling of the North Atlantic during the LIA intensified the northeast trade winds, which favored the transport of moisture to the Amazon. This is the opposite of what happens in years when the northeast trade winds are less intense: they tend to be drier years,” Cruz said.

Once the cloud masses in the ITCZ reach the Amazon, they contribute moisture that is richer in 16O to the SACZ. The extra amount of this isotope is recorded by speleothems.

During the MCA, the northern hemisphere’s warmer climate formed a low-pressure zone to which wet winds converged from the South Atlantic. “The ITCZ moved further north. All of South America became drier,” Cruz said.

###

The paper: https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2017GL076838

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65 thoughts on “Study: “Little Ice Age” also affected South American climate

  1. Ha. They knew the LIA was global since the late 90s.

    Climategate email 3759.txt

    Hi Keith [Briffa],

    Here is the Oroko Swamp RCS chronology plot in an attached Word 98 file and actual data values below. It certainly looks pretty spooky to me with strong “Medieval Warm Period” and “Little Ice Age” signals in it. It’s based on substantially more replication than the series in the paper you have to review (hint, hint!). In terms of rbar, sample size, and eps, it is probably okay back to about AD 980 at this time. I still have 3-4 more subfossil sections to process, but it is doubtful that the story will change much. When I come over in October, I am thinking about asking Jonathan Palmer to come over from Belfast for a visit. What do you think about that?

    Ed

    Oroko Swamp is in New Zealand.

    • “Ha. They knew the LIA was global since the late 90s.”
      Well, that email says it was present in New Zealand. But you don’t need to poke into people’s emails for that revelation. Ed Cook published that data, in a 2002 paper helpfully titled
      “Evidence for a ‘Medieval Warm Period’ in a 1,100 year tree-ring reconstruction of past austral summer temperatures in New Zealand”
      It focussed on MWP, but dealt with the LIA too; you can’t really have one without the other.

      • Yep. The Little Ice Age (LIA) would be the Little Normal Age (LNA) if it were not preceded by the Medieval Warm Period (MWP). Therefore you cannot have the one without the other; as you correctly state.

        • yes the MWP – only an extreme weather event over the same tiny portion of the globe for 300+ years

        • The vicar of CO2 on earth his holy Mann says you are wrong, who are you to question his authority??

      • both new zeeland and the uk are great teleconnected places.

        phil jones has sone work on this

      • I notice that Cook 2002 added the actual measured Hokitika temperature data after 1958 to the tree-ring reconstruction (Fig 3), because of a perceived deterioration in the Oroko swamp data after 1958 due to the commencement of logging. The resultant graph is a noticeable increase in temperatures after 1958. Is that practice still regarded as valid?

    • See also Gergis, Dome C, Law dome, etc
      Mann Jones 2003 where they zero weight dome C
      See S Mcntyre – regarding other critisim of Pages 2k

      Yes they knew the elevated SH during mwp .

    • funny a few sparse proxies and you extrapolate.

      two or three caves in brazil….

      if these were rain gauges youd be skeptical.

        • Once again Mosher inadvertantly gives away his tell, that being a lack of knowledge and research. Either that or he’s intellectually dishonest…

          Hmm… I’d wager the latter, if I was a betting man

      • except
        A) law dome is one of the highest resolution proxies
        B) Okasa swamp
        C) See Mcntyre critisism of pages 2k and gergis
        D) too many other proxies screened out via post / ex ante screening

      • steve. I bet you also believe there are currently 17+ genders..maybe more to come; is that accurate? I’m just trying to nail down the depths of your self-deception and detachment from reality

      • I might be mistaken, but I believe that 3 caves beat a single tree. And a full house beats two pair.

      • funny a few sparse proxies and you extrapolate. two or three caves in brazil….

        The one bristlecone pine representing the whole world beats that.

  2. We are going through a big drop in Atlantic ocean temps from last year to this year and the southern North Atlantic is loaded with Saharan dust and dry air. Compare this to last year where there was ample moisture and the waves coming off Africa training across the area and turning into devastating hurricanes.

    I don’t know exactly why the waters have cooled so much, but this very much shows the effect the waters of the Northern Atlantic have on where the ITCG sets up and especially rain events throughout the summer on not only the Carribean/GOM/SE US, but farther south into Central and South America.

    Empirical data, no computer model.

  3. From above text: “A new study published in Geophysical Research Journal shows that the so-called Little Ice Age – a period stretching from 1500 to 1850 ….”
    Now I wonder where I have seen that 1850 date recently?
    Got it!! “…..graphical depictions of temperature coming from Dr. Ed Hawkins.
    Spiral graph indicating GLOBAL TEMPERATURE CHANGE (1850 – 2017).”
    Obviously the starting year being selected as 1850 (and this also being the year that the LIA is considered to have ended) is pure coincidence because otherwise it could be considered as fraudulent misrepresentation; by an overly suspicious person.

    • “(and this also being the year that the LIA is considered to have ended)”…

      Which is totally arbitrary…..it could have just as easily ended in 1900, 1950, etc…..

      • I strongly suspect that the year 1850 was selected because it represented a minimum with regard to recent past temperature. To select a starting year closer to the present (say 1930 AD) supposing it was arbitrarily selected without an agenda; would defeat the AGW narrative. Similarly selection of a starting year further into the past (say 1000 AD) would likewise defeat the AGW narrative because global temperatures were higher during the Medieval Warm Period. Hence my suspicion that the starting year was selected with “intent”.

      • How come I voted up from 2 to 3 and it show a -1? This is the third time this has happen

      • They had a very good reason for cherry picking those dates.

        PS: It’s not a conspiracy to note that when it comes to global warming, noting in wikipedia can’t be trusted.

      • You advise check Wikipedia, I advise you to provide some facts to back up that outburst. See, if I wanted sheer conjecture, I could check Wikipedia, if I want facts, Wikipedia is NOT the place I would look. Just in case I was too subtle for you.

  4. “During the MCA, the northern hemisphere’s warmer climate formed a low-pressure zone to which wet winds converged from the South Atlantic. “The ITCZ moved further north. All of South America became drier,” Cruz said.”

    WR: For me this is the most interesting part, because it reminds me to what was happening in the last half century. What before was called ‘Global Warming’ was centered on the North Atlantic. A subsurface warm water intrusion in the Arctic area and consequent mixing with colder upper layers did melt the ice. More water vapor evaporated and the rise of more moisture air attracted other warm air and low pressure areas from the south-west, enhancing any warming effect. More low pressure activity direction Arctic made winters in Western Europe very mild and wet, last decades.

    Temporary (decades, a century or some century’s) there must be such a shift northwards within the rather stable period the Holocene is. It created warming like in the Medieval Period or during last century. The reversed (southward) shift of zones resulted in cooling, globally – but especially in the North Atlantic region, like during the Little Ice Age.

    Why the North Atlantic plays such a big role is because of water vapor. Melting ice enhances the quantity of water vapor over the Arctic and North Atlantic. Water vapor is our main radiation absorbing gas: the Earth as a whole cooled less because a large region warmed. Besides, there were large albedo effects because ice and snow reflection diminished. And the mentioned change in weather patterns: more low pressure activity.

    The cause of all: a warm water influx from the Atlantic below the colder but fresher and less dense surface layer of the Arctic. With consequent effects during one or more decades. I suppose that the same process has caused the warming of the Thirties, I remember low ice extent reported in the Arctic.

  5. I think you will find there is alot of 1000 deg magma warming the passive ocean about there, on the mid atlantic ridge. That also varies quite a lot. Check out Maya Tolstoy’spaper on the variable activity at the mid atlantic ridge and other divergent plat boundaries. And mine when I finally publish it.

  6. I’ve been told repeatedly that ” MCA (formerly known as the MWP) and the LIA) was local and not world wide. How could it be otherwise? CO2 levels were constant, therefore temps couldn’t have changed. Because co2 is the control knob for temp…
    That’s the story and AGW is sticking to it. Or like the “tipping point”, they just quietly let it slip into the forgotten files, ‘ we never said that’.

  7. I’ve been telling you all for years that when the sun is less active the jet stream tracks in both hemispheres become more meridional and drift towards the equator. The opposite when the sun is active.
    This provides evidence in support.
    The ITCZ is balanced between the two hemispheric circulation systems.

  8. Obviously Fake News.

    I was told 20 years ago on Usenet (ask your grandparents what that was) by the highly qualified and totally unbiased William Connolley that the Little Ice Age was:

    a) very, very minor;
    b) very, very short; and
    c) very, very local (Europe only. Except for some small stuff in North America. Ok, maybe a bit in Asia, but THAT’S ALL, except for perhaps some in South America as well. But nothing in Antarctica (that’s his specialty, after all).

    • So all those stalagmites around the world (Brazil, Australia, South Africa, et al) must all be wrong and are not to be believed.

      The Hokey Schtick didn’t show the LIA from the Wolf Minimum to the Dalton Minimum, nor did it show the MWP, All that stuff was just weather and had nothing to do with climate, as told in the Hokey Schtick, The Source Of All Climate Knowledge. How dare you even admit stalagmites show anything at all; they’re just inert rock , after all. If you do, you will be sued for Defamation and Bad Mouthing the Oracles.

      (AR6 must be nearly ready for publishing for all the rubbish appearing and I don’t mean plastic trash in the oceans …)

      • “(AR6 must be nearly ready for publishing for all the rubbish appearing and I don’t mean plastic trash in the oceans …)”

        You’re probably right, this is known as “battlefield preparation”. Although if the polls are correct, it will be a big yawn outside of the media bubble. Hard to believe, isn’t it, that thee is a very large gap between what people actually care about, and what we’re told is very, very important.

        And I wonder what AR6 will have in the way of “sure, the skeptics pointed in out years ago, and we mocked them for it, but we’re including it now because WE discovered it, not them”.

        See: the sun as major climate driver, clouds, urban heat islands, The Pause, etc.

  9. This makes for fascinating reading. https://en.wikipedia.org/wiki/Last_Glacial_Maximum

    Colder periods are not just dominated by ice, but more arid as well. Another LIA would probably mean millions of excess deaths due to higher food and energy costs, another period like LGM might end human civilization and reduce the entire population to millions.

  10. I keep throwing out the challenge: find a single glaciologist who doesn’t take a global LIA for granted. You can’t. –AGF

  11. Valdir Felipe Novello is not the IPCC-type of climate scientist trying to push a dubious hypothesis. As a paleoclimatologist he just presents the evidence he finds in cave speleothems instead of making articles from computer climate model outputs. Two years ago he published another article on Brazilian cave speleothems:

    Novello, V.F., et al. (2016). Centennial-scale solar forcing of the South American Monsoon System recorded in stalagmites. Scientific reports, 6, 24762.
    https://www.nature.com/articles/srep24762

    There he showed that the South American Monsoon is under control of solar variability and follows the 208-yr de Vries solar cycle.

    “The main focus of this study was to document, for the first time, a pervasive, 208-year periodicity of the South American monsoon, which persists throughout the past 1500 years. This periodicity is apparent in our new high-resolution speleothem record from south-central Brazil, located in the core of the SAMS. The documented coherent in-phase relationship on centennial timescales between the precipitation in our speleothem record and a reconstruction of total solar irradiance is consistent with model simulations, which indicate that tropical precipitation is sensitive to solar forcing10,12 and that the southern hemisphere monsoon in particular responded in a sensitive way to solar forcing during the past millennium7.”

    https://www.researchgate.net/profile/Valdir_Novello/publication/301549114/figure/fig4/AS:353270653571083@1461237695949/Comparison-between-anomalies-in-total-solar-irradiance-32-TSI-in-W-m-2-blue-and-our.jpg

    Figure 4. Comparison between anomalies in total solar irradiance32 (TSI, in W m−2, blue) and our ALHO6 δ18O record (in permil, purple). Thin lines show raw anomalies; thick lines are low-pass filtered with a nearest neighbor 208-yr window using a Gaussian kernel. ALHO6 was detrended with a 3rd order polynomial function prior to filtering to remove long-term trends associated with mean state changes from Medieval Climate Anomaly (MCA) to Little Ice Age (LIA). Orange (blue) shading highlights periods of above (below) average low-pass filtered TSI respectively, which tend to coincide with decreased (increased) δ18O.

    I have yet to read his new article, but according to the abstract it deals with an issue that escapes most people. The local character of climate proxies makes them register only the changes that take place at the site, and speleothem records from different regions are affected very differently by changes in the Convergence Zone. Interpretation of proxies is not simple.

    The LIA was global and is well registered in glaciers all over the world, however its impact was bigger in the North Atlantic region, Siberia and Northern China. These are climatic hotspots that are more sensitive to changes. Particularly the North Atlantic region.

    • Javier:

      As you must know, it is IMPOSSIBLE to distinguish changes in solar irradiance obtained from the Earth’s surface as to whether they are caused by changes in the sun’s output, or simply due to changing SO2 aerosol levels in the atmosphere, especially during periods of extensive volcanism.

      As a result, the graph which you show is highly misleading.

      • Burl:

        Paleo changes in solar activity are inferred from cosmogenic isotopes ¹⁴C and ¹⁰Be. We don’t have any reason to suspect that the production of these isotopes in the atmosphere by cosmic rays hitting oxygen and nitrogen atoms is affected by the presence of stratospheric sulfate from volcanic eruptions. Therefore it is a safe assumption within our present knowledge that the changes in solar irradiance inferred from proxy records have little to do with volcanic eruptions.

        • Javier:

          I had assumed that the Paleo changes were obtained from proxy measurements of temperatures at that time. I was not aware that they were inferred from cosmogenic isotopes. Thank you for educating me.

          You also said “We don’t have any reason to suspect that the production of these isotopes in the atmosphere by hitting oxygen and nitrogen atoms is affected by the presence of stratospheric sulfate from volcanic eruptions”

          However, there actually IS a reason to suspect that sulfate emissions have an effect: If they are present, they will intercept some of the incoming cosmic rays, so that fewer isotopes will be formed, giving the impression that the sun’s radiance has decreased.

          This conjecture is easily verifiable.

          Since essentially all La Ninas are caused by the volcanic insertion of SO2 aerosols into the stratosphere, one would expect that “decreases” in solar irradiance would occur whenever there is a La Nina, because of the higher levels of SO2 aerosols in the atmosphere at that time.

          Using a plot of Solar Irradiance, 1880-2012, there is essentially a 1:1 correlation with the minima of a change in solar irradiance and the presence of a La Nina, as well as with a peak in solar irradiance and the presence of an El Nino (caused by decreases in SO2 aerosol emissions).

          Thus, at this point, I believe one can safely state that all observations of supposed changes in solar irradiance are actually due to changing levels of SO2 aerosols in the atmosphere!

          • Burl:

            sulfate emissions have an effect: If they are present, they will intercept some of the incoming cosmic rays, so that fewer isotopes will be formed

            This is not correct. Cosmic rays are highly penetrating and the atmosphere is almost transparent to them. The presence of tiny amounts of another gas in the atmosphere does not change the chances of collisions that are already highly unlikely, yet statistically certain.

            essentially all La Ninas are caused by the volcanic insertion of SO2 aerosols into the stratosphere

            I would like to see the evidence for that. It is the first time that I read that La Niña is caused by volcanic eruptions, and quite frankly, I am very skeptical.

            Using a plot of Solar Irradiance, 1880-2012, there is essentially a 1:1 correlation with the minima of a change in solar irradiance and the presence of a La Nina, as well as with a peak in solar irradiance and the presence of an El Nino

            Again, I would like to see the evidence for that. In any case a relationship between ENSO and solar activity would not need neither cosmic rays, nor volcanic eruptions.

          • Javier:

            You said that “the presence of tiny amounts of another gas in the atmosphere does not change the chance of collisions”

            SO2 aerosols are not a gas, but are fine droplets of Sulfuric Acid, whose size is perhaps i mm in diameter, as compared to about 1.8 E-10 meters for diatomic oxygen. Since they are millions of times larger than an oxygen molecule, and are located in the stratosphere where oxygen is scarce, the increased chance of collisions with them undoubtedly explains the observed correlation with their presence and decreases in “solar irradiance”.

            “It is the first time that I have read that La Nina is caused by volcanic eruptions”

            A La Nina follows essentially every VEI4 and higher eruption, unless it occurs during an El Nino, or has low SO2 emissions. The La Nina typically lags the date of eruption by a year or more, depending upon ENSO temperatures at the time of the eruption (it takes time for their aerosols to circulate around the globe)

            I will try to post a copy of the graph shortly.

            “a relationship between ENSO and solar activity would not need neither cosmic rays nor volcanic eruptions”

            Volcanic eruptions ARE the cause of most La Ninas, and many El Ninos (volcanic induced El Ninos), with the balance being man-made.

    • You sort of answered the question I have not yet asked, but I’m going to ask it anyway, cuz you didn’t really answer. Most commenters are apparently distracted by the seeming support of a global LIA/MWP, a question which has probably been answered a number of times by other proxies. Which based on the short read of this article, I’m not entirely certain that’s what the paper shows. But even more importantly… how did they calibrate this proxy? I don’t mean the selection of samples (though 4 samples from 2 caves hardly makes a “robust” database, I agree with Mosher above, this is pretty thin), the collection, or even the processing to analyze the annual(?) isotope ratios. Rather, how did they compare the isotope ratios against something, anything, to verify that a change in the ratio means what they think it means? Are y’all gonna make me read the paper myself to see if they did this? Or has someone already read the paper, and can answer me in one sentence or less, has this been calibrated to effectively prove that the change in ratio means what they say it means? We have countless examples of, for example, tree rings (which I believe can be far worse at anomalous readings because a missing ring actually meant that a sheep nibbled off the bark that year, not that there was a summer without a summer) that turns out fatter and thinner rings bear almost no relationship to temperature, but rather to moisture levels or even atmospheric CO2 levels, maybe the level of livestock grazing each year. What has this proxy been vetted against to verify a change in isotope ratios means what they say it means? And my question mark in parentheses above, can the researchers be certain that they have properly mapped the time scale? What if a ring in their sample only means a wet period interspersed with a dry period, that may or may not occur at yearly intervals? Methinks this explanation of methodology should occupy a significant portion of this paper.

      • Isotopic fractionation is the basis of a majority of proxies, so a considerable effort has gone into understanding the behavior of different isotopes, thus it is not controversial to propose that more precipitation is accompanied by less δ18O. However for a particular speleothem to be useful it is important that there hasn’t been significant changes in the cave’s atmosphere, and the source of the water and the means by which it gets into the cave have not changed over the period analyzed. The authors usually go as far as they can to support the validity of their interpretation, but in the end the biggest support comes from different proxies from different places showing an overall similar climatic evolution.

        What the authors say about this is:

        “2.1 Records located to the southwest of the SACZ position (State of Mato Grosso do Sul)

        We obtained two new δ18O records from stalagmites sampled in a cave of southwestern Brazil, namely stalagmites JAR4 and JAR1 (Supplemental Figure S1), both collected in Jaraguá cave. The sample JAR4 is ~13 cm long and grew continuously between ~1190 to 2000 AD. Its isotopic profile consists of 238 δ18O values linearly interpolated between 20 U/Th dates (Supplementary Table S1), which provides a resolution of ~ 1 data point every 3 years. The sample JAR1 is a ~28 cm long stalagmite that provides a continuous isotopic record between ~442 to 1451 AD with 423 δ18O data linearly interpolated between 15 U/Th ages (Supplementary Table S1), providing a resolution of ~3 years.

        Jaraguá cave is located in Bonito city (21°05’ S, 56°35’ W, ~570 m above sea level) in the state of Mato Grosso do Sul (MS), southwestern Brazil (the description of the cave is in the Supplemental Material – Text S1). The climate in Bonito City is tropical with a three-month long dry season during austral winter, with annual precipitation of 1400 mm and with mean temperature over austral winter and summer of ~20°C and 26°C, respectively. A separate δ18O record derived from different stalagmites obtained in Jaraguá cave covering the last deglaciation was previously published in Novello et al. (2017). In the latter article, using a monitoring of environmental parameters, the authors showed that the amount effect exerts the main control on the δ18O fractionation at our study site on both seasonal and interannual timescales and that the cave atmosphere does not have a significant influence on the isotopic fractionation during stalagmite formation. In addition, the δ18O profiles of the two stalagmites overlap between ~1191 and 1451 AD, confirming a similar isotopic fractionation on both samples (Figure 2). Thus, we interpret the δ18O profile in the JAR4 and JAR1 stalagmites as varying primarily in response to changes in rainfall amount, with more negative δ18O values reflecting more precipitation, and vice-versa. We are confident that this interpretation is robust for the past two millennia, as significant changes in seasonality of precipitation or changes in moisture source are unlikely to have occurred during this time interval (Vuille et al., 2012).

        2.2 Records located to the northeast of the SACZ position (State of Goiás)

        Additional speleothem records were obtained in central Brazil, where δ18O was sampled on two stalagmites, the stalagmite SBE3 from São Bernardo cave and the stalagmite SMT5 from São Matheus cave (Figure 1). Both caves are located in the same karstic region and their entrances are within approximately 10 km of one another. We sampled a 37 cm long portion on stalagmite SBE3 for isotopic analyses, covering a period between ~1123 and 2010 AD. The isotopic profile of SBE3 consists of 1116 δ18O values constrained by 11 U/Th ages (Supplementary Table S1), providing a sub-annual resolution. The isotopic profile of stalagmite SMT5 contains 576 δ18O values, constrained by 4 U/Th ages (Supplementary Table S1) and sampled over 17 cm of the speleothem. This interval covers the period between 264 to 1201 AD, resulting in an average resolution close to annual.
        The São Bernardo and São Mateus caves (13.81°S, 46.35°W, ~631 m above sea level) are located in the Terra Ronca State Park (PETER) in the state of Goiás (GO), near the border to Bahia State (BA), the description of the caves and monitoring information of them are on the Supplemental Material –Text S2. The climate in this region is tropical semi-humid with a mean annual precipitation of ~1270 mm. The rainy season extends from October to April, while rainfall is basically absent between May and September. The mean annual temperature is 24.0°C with the monthly mean ranging between 22.5°C (July) and 25.8° (October) (Moquet et al., 2016).

        The most recent 140 years of the SBE3 record were published by Moquet et al. (2016), which, together with the monitoring performed in the São Bernardo cave, demonstrates that the δ18O record co-varies with the amount of rainfall associated with SACZ activity in the central region of Brazil on interannual time scales. Therefore, the oxygen isotopic signature of speleothems from this cave are being used in this study to reconstruct past SACZ activity.”

        • OK, so they’re saying, both JAR4 and SBE3 timelines can be matched against contemporaneous rainfall records, and calibrate them against that? As well as getting the same ratios as the Novello et al. (2017), for the same time periods? Actually, I’m not clear on what they did with Novello. Are both the Novello results and the results of these 4 samples all plotted on the same graph, somewhere? But OK. I can see how they have confidence in their work. Thanks, Javier.

  12. OK, I get it that the physically heavier ’18O’ might precipitate first but to therefore conclude that this leaves LESS ’18O’ to precipitate later puzzles me. For this to be true there must be no meaningful resupply of the ’18O’ water molecule (ie only ’16O’ is left. And if THAT were true, given the millions and millions of years the earth has been rained on there should be NONE by now. Am I missing something?

    • It isn’t exactly like that, NW Sage. You can think of ¹⁸O as being a little lazier in getting to the gas phase and a little more active in getting into the liquid phase, and this difference being very dependent on temperature, but also affected by salinity. As a water molecule moves through the water cycle there are multiple fractionations each affecting the ratio. The rain from a cloud near the sea has more ¹⁸O than the rain from the same cloud 100 km inland, as the ¹⁸O is being depleted from that cloud.

      Therefore the ¹⁸O/¹⁶O can be used to determine changes in precipitation (more precipitation usually less δ¹⁸O, but depends on location and source), changes in temperature (warmer, more δ¹⁸O), and changes in ice volume, as the ice is very depleted in ¹⁸O, particularly when it is very cold, and when ice volume is very big, ocean water has more ¹⁸O that goes into the shell of little critters.

      If you are still interested in more info, I highly recommend this presentation on ¹⁸O isotope ratios as climate proxy:

      https://www3.nd.edu/~nsl/Lectures/phys20054/15Lecture%2011%20Climate%20Proxies-2.pdf

      • Javier,
        “The rain from a cloud near the sea has more ¹⁸O than the rain from the same cloud 100 km inland, as the ¹⁸O is being depleted from that cloud.”

        Wouldn’t transpired and evaporated water vapor rising from the surface near the sea be correspondingly rich in 18O, so as to maintain isotope ratios in the rainfall falling further inland?

        SR

  13. First published: 28 May 2018: Wasn’t there a study done like 10 years ago saying the same thing? About the time that the alarmist was saying the LIA was just a northern hemisphere thing?

  14. 18O ? Isn’t it either ¹⁸O or O-18?

    It’s filtering out html superscripts. But when one uses the superscript characters instead, the superscripts ¹, ², ³ render with a different font size to: ⁴, etc. The way to overcome that (render the font uniformly) is put the whole inside a html <code> block. I.e. Render it as a monospace font.

  15. Just imagine: all of this documented by nature before 1850 and the beginning of global industrialization and its associated human-caused global warming meme.

    Why, this must be an example of what they call pure science.

  16. A politically incorrect stream-of-consciousness rant can be an ugly thing, and it’s about time I wrote one.

    1960 is the Real [tm] magic climate year. That’s the year when, according to Michael Mann and the rest of the brains behind RealClimate [tm] and the CRU and the IPCC consensus, Keith Briffa’s proxy trees stopped being accurate treemometers and began their careers as tree-niers [tm].

    What made the trees do that? Did they suddenly register as Republicans at the same time? Probably not, if they were Russian trees. Unless there was collusion. Or, maybe some big oil and gas money bought them off or hired some mobsters to make them an offer they couldn’t refuse… we know where your pine cones go to school… be a shame if anything happened to them …

    The same climate magic happens every glaciation cycle, when, 800 years after the beginning of a post-glaciation warmup / meltdown, whatever causes the first 800 years of warming suddenly and magically switches off and hands the job of the remaining Holoscene-style warming off to that portion of the so-called “greenhouse effect” (GHE) that is due solely to a few extra parts per million of CO2 in the atmosphere that managed to out-gas from a warming ocean over the previous 800 years. What is this mysterious force? Why did it switch off? Where is it? Why can’t we find it?

    No one knows. Michael Mann doesn’t know, Gavin Schmidt, Kevin Trenberth and even James Hanson doesn’t know. If they did, they would rewrite RealClimate’s lamer than lame ass explanation about this. They only know it did go away, by magical assertion. And that CO2 took over. The same level of not knowing combined with curious absolute certainty is seen in enlightened, god-like beings from the political sphere such as Barack Obama and his less than god-like advisors John Holdren, Valarie Jarrett, Joe Biden and Cass Sundstein. Real academic scientists like lesbian glaciologists don’t know what performed this magic, nor do celebrities and feminists, like Naomi Oreskes, Naomi Klein, Naomi Watts or Naomi, er, make that Ashley Judd. It’s safe to say that no one named Naomi, knows. Climate Barbie and Christina Figueres do not know, but true to their outwardly perceived gender, they ARE milking it. Trans and Cis Jenner-benders do not know. This magical force is obviously very clever, to out-smart such men and women and hermaphrodites at the forefront of modern-post-modern-post-normal sciency-social-ness. God (if he/she/it exists) protect us from appeals to authority if THIS is the kind of authority you’re talking about.

  17. so of course the question for the warmists is thus – what melted all these massive ice sheets if there were no industrialized societies ? how do you possibly believe that a trace gas CO2, increasing from 3 parts per 100,000 to 4 parts per hundred thousand, is the control know of the climate? they likely know this of course, but it’s a front for the command and control agenda behind this whole contrived AGW scare. fortunately, judging by some of the very informed commentators on this site, this hoax is being challenged at every opportunity.

  18. Another gold nugget. Tks WUWT. Would appreciate the full paper if there’s a link to it.

    This and the NZ paper indicate these as global. However these were mild compared to similar earlier in the Holocene. (I am not a climate scientist or whatever; just seeking explanations for evidence). For explanation see link: https://melitamegalithic.wordpress.com/2018/07/24/searching-evidence-update/

    These phenomena are not only weather/climate related, but also have had extreme influence on our collective histories.

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