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Evidence Of MWP In Argentina

December 24, 2015

By Paul Homewood  




Rog has news of the latest study, suggesting that the MWP was real, this time in Argentina:


Vilanova et al. (2015) developed a multi-proxy millennial environmental record from sediment cores extracted from Laguna Nassau, a shallow lake that apparently developed within a blowout depression in the semi-arid sandy lowlands of the Western Pampas of Argentina.

And as they go on to report, “this multi-proxy stacked record reveals the evolution of an incipient water body subjected to warm and dry conditions from ~900 to 770 cal yr BP, an interval that is coeval with the Medieval Climatic Anomaly,” which is also more commonly known as the Medieval Warm Period or MWP.

Continuing, the five researchers write that the buried remains of the highest percentages of Celtis — commonly known as hackberries or nettle trees, which represent a genus of about 60-70 species of deciduous trees widespread in warm temperate regions — in the Laguna Nassau pollen record suggest the existence of “a semi-arid climate and indicate that [drum roll] drier and warmer conditions than today predominated in the area from about 900 to at least 770 cal yr BP.”

And so we have yet another well-documented example of the pure and simple fact that the much-studied Medieval Warm Period likely was somewhat warmer than the Current Warm Period has been to date, and during a time when the atmosphere’s CO2 concentration was only about 280 ppm, compared to the approximate 400 ppm of today.

And these facts further suggest that the historical increase in the air’s CO2 content that began with the Industrial Revolution may have had nothing at all to do with the development of the Current Warm Period, which still has a substantial way to go before it reaches the degree of warmth that characterized the peak warmth of the MWP.


This adds to many other studies which show evidence of the MWP and LIA in South America.



For instance, this paper by Polissar et al, concerning Venezuela:




Back in 1986, Lonnie Thompson was honest enough to admit the same in Peru:


The analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent. Annual variations in visible dust layers, oxygen isotopes, microparticle concentrations, conductivity, and identification of the historical (A.D. 1600) Huaynaputina ash permit accurate dating and time-scale verification. The fact that the Little Ice Age (about A.D. 1500 to 1900) stands out as a significant climatic event in the oxygen isotope and electrical conductivity records confirms the worldwide character of this event.


It was also Thompson who wrote in 2003 that:

For the Quelccaya Ice Cap (13.93°S, 70.83°W), this work revealed that peak temperatures of the MWP were warmer than those of the last few decades of the 20th century.



Areneda et al found similar in Chile:


These data allow us to infer that the last maximum advance of Cipreses glacier, in Chile, attributable to the ‘Little Ice Age’ occurred around AD 1842. The first historical retreat was recorded in 1858 and, since then, the glacier has shown a clear retreating trend with no new advances. All this information was compared with the historical data gathered for San Rafael glacier, which shows the occurrence of a cold period contemporary with the European LIA.



Also from Areneda:


Past ice lobe behaviour at Laguna San Rafael is described in documents provided by Spanish and then Chilean explorers from the late seventeenth to the early twentieth centuries. These records begin in AD 1675, when temperate conditions, probably similar to those at present, prevailed. At that point, the glacier was confined within its valley, not penetrating the Laguna. The glacier advanced noticeably during the nineteenth century and probably reached a maximum position for the `Little Ice Age’ around AD 1875. The historical sources suggest a slight retreat in AD 1904 in relation to the conditions prevailing 29 years earlier. The historical data show that the eighteenth to nineteenth century cooling period at San Rafael glacier was within the temporal window of the European `Little Ice Age’. This work provides independent, direct historical evidence for the occurrence of this event in southern Chile.


And in Patagonia, the retreat of the  Jorge Montt Glacier is uncovering the remains of 400 year old forests.




These studies don’t necessarily prove that temperatures were as warm in the Middle Ages as now in South America. But what they do show in conclusive fashion is that the there was a marked cooling there during the Little Ice Age, and that there was, by definition, a much warmer period before.

  1. December 24, 2015 4:23 pm

    Wikipedia waffles about the North Atlantic and ‘substantial uncertainties’.

    They then contradict themselves by asserting: ‘globally the Medieval Warm Period was cooler than recent global temperatures.’

    What happened to the ‘substantial uncertainties’ Wiki? 😉

    • Billy Liar permalink
      December 24, 2015 7:03 pm

      I believe that Wiki entry has been ‘Weaselly’ worded.

    • December 24, 2015 7:37 pm

      From the Wikipedia link: “Alaska experienced three time intervals of comparable warmth: AD 1–300, 850–1200, and post-1800”

      More empirical evidence has been found in recent years of the MWP – the remains of mature coniferous trees which were growing during the MWP – then mowed down by advancing glaciers (Mendenhall and Exit) being exposed in recent years as the glaciers once more retreat up the mountain. Another couple hundred years of this life giving warmth, and perhaps those forests will thrive once again – for a while.

  2. kennethrichards permalink
    December 25, 2015 7:18 pm
    Here, we present evidence for glacial retreat corresponding to the MWP [Medieval Warm Period] and a subsequent LIA [Little Ice Age] advance at Rothera Point (67°34′S; 68°07′W) in Marguerite Bay, western Antarctic Peninsula. Deglaciation started at ca. 961–800 cal. yr BP or before, reaching a position similar to or even more withdrawn than the current state, with the subsequent period of glacial advance commencing between 671 and 558 cal. yr BP and continuing at least until 490–317 cal. yr BP. Based on new radiocarbon dates, during the MWP, the rate of glacier retreat was 1.6 m yr−1, which is comparable with recently observed rates (~0.6 m yr−1 between 1993 and 2011 and 1.4 m yr−1 between 2005 and 2011).

    Click to access Richey_etal_2007.pdf

    [C]entennial-scale sea surface temperature (SST) oscillations of 2–3 °C occurred during the past 1–2 [thousand years]. Two multidecadal intervals of sustained high Mg/Ca indicate that Gulf of Mexico sea surface temperatures (SSTs) were as warm or warmer than near modern conditions between 1000 and 1400 yr B.P. [before present] Foraminiferal Mg/Ca during the coolest interval of the Little Ice Age (ca. 250 yr B.P.) indicate that SST was 2–2.5 °C below modern SST. Four minima in the Mg/Ca record between 900 and 250 yr B.P. correspond with the Maunder, Spörer, Wolf, and Oort sunspot minima, suggesting a link between changes in solar insolation and SST variability in the Gulf of Mexico.
    [S]ea surface temperature and salinity records from the Makassar Strait, Indonesia, show a long-term cooling and freshening trend, as well as considerable centennial-scale variability during the last millennium. The warmest temperatures and highest salinities occurred during the Medieval Warm Period (MWP), while the coolest temperatures and lowest salinities occurred during the Little Ice Age (LIA). These changes in the western Pacific, along with observations from other high resolution records indicate a regionally coherent southern displacement of the Inter-tropical Convergence Zone during the LIA
    The results suggested that the mean SSTs [sea surface temperatures] around AD 990 (±40) and AD 50 (±40) were 28.1 °C and 28.7 °C, +0.8 °C and +1.4 °C higher than that during AD 1994–2005, respectively. These records, together with the tree ring, lake sediment and literature records from the eastern China and northwest China, imply that the temperatures in recent decades do not seem to exceed the natural changes in MCA, at least in eastern Asia from northwest China to northern SCS.
    Here we present new data from the Ross Sea, Antarctica, that indicates surface temperatures were ~ 2 °C colder during the LIA, with colder sea surface temperatures in the Southern Ocean and/or increased sea-ice extent, stronger katabatic winds, and decreased snow accumulation. The McMurdo Dry Valleys [Antarctica] were 0.35°C warmer during the MWP than during ME [modern era], accompanied by warmer conditions in the Ross Sea.

    Click to access Tyson.pdf

    The Little Ice Age in South Africa, from around AD 1300 to 1800, and medieval warming, from before 1000 to about 1300, are shown to be distinctive features of the regional climate of the last millennium. The climate of the interior of South Africa was around 1°C cooler in the Little Ice Age and may have been over 3°C higher than at present during the extremes of the medieval warm period.

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