Search Results for “medieval” – Page 2

Claim: Civilization-Collapsing Megadroughts of Medieval Times Could Be in Store for a Warming Earth

July 29, 2019

https://www.livescience.com/66032-medieval-megadroughts-return-global-warming.html?utm_source=ls-newsletter&utm_medium=email&utm_campaign=20190726-ls By Charles Q. Choi Scientists may have unraveled the mystery of what triggered decade-long droughts during medieval times in the American Southwest. These so-called megadroughts were so devastating that entire civilizations may have collapsed in their wake. These findings suggest the risk of megadroughts may rise due to global warming, scientists added. From the 800s to the 1400s, about a dozen megadroughts struck the American Southwest, and all lasted longer than a decade. “There weren’t a whole lot of people there compared to today, but prior work has suggested that a number of native societies in the Southwest experienced megadroughts that were tied to the collapse of their civilizations,” said study lead author Nathan Steiger, a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory. “People don’t think megadroughts are the only reason why they collapsed, but they do think they were major contributing factors.” These megadroughts mysteriously ceased in the American Southwest about the year 1600. Scientists have sought to uncover what caused these past giant dry spells to shed light on whether, how and where they might happen in the future. [Nature’s Arches: Photos of Stunning Sandstone in the American Southwest] “Eighty percent or more of the water used by the American West is used for agriculture,” Steiger said. “A megadrought could fundamentally change how communities are supported, how farmers in the West and California in particular do work, what they plant, if farming is even possible or not.” Now, the researchers suggest they may have for the first time developed “a comprehensive theory for why there were megadroughts in the American Southwest, and why they stopped,” Steiger said. Steiger and his colleagues developed a global reconstruction of aquatic and climate data and sea-surface temperatures spanning the past 2,000 years. They identified 14 droughts lasting more than a decade, all of which took place before 1600. The scientists found three key factors were apparently linked to each medieval megadrought. The first involved “positive radiative forcing” — that is, a rise in the amount of energy that Earth absorbed from the sun. The next involved warming in the North Atlantic Ocean. The last factor involved severe and frequent La Niña events — unusually cool waters in a belt 5,000 miles (8,000 kilometers) long across the equatorial Pacific Ocean that previous research found could trigger floods, heat waves, blizzards and hurricanes worldwide. During medieval times in the American Southwest, a drop in volcanic activity — which would have spewed out ash to block the sun — along with an increase in solar activity such as solar flares likely increased the amount of heat the area absorbed (positive radiative forcing). The overall rise in heat would have dried out the area. At the same time, warmer Atlantic conditions combined with strong, frequent La Niñas could have reduced rainfall. All in all, the scientists found La Niña events played a role that was twice as important at causing megadroughts as the other two factors. La Niña is Spanish for “little girl” and is the counterpart of El Niño, which is Spanish for “little boy” and involves unusually warm waters in the same area of the equatorial Pacific Ocean. South American fisherman named El Niño for the baby Jesus, after noticing that the ocean would heat up around Christmastime. The researchers cautioned that any potential future megadroughts will remain difficult to predict, since future El Niños and La Niñas remain difficult to model and forecast. However, they also cautioned these megadroughts may return in the near future due to emissions of greenhouse gases such as carbon dioxide, which trap heat from the sun and boost positive radiative forcing, The scientists detailed their findings online July 24 in the journal Science Advances.

Study: The Medieval Warm Period in Antarctica

July 25, 2019

http://co2coalition.org/2019/07/22/the-medieval-climate-anomaly-in-antarctica/ The Medieval Climate Anomaly in Antarctica By Sebastian Lüning, Mariusz Gałka and Fritz Vahrenholt Highlights Opposing temperature trends of the Medieval Climate Anomaly (MCA) in Antarctica. MCA warming found in Antarctic Peninsula and Victoria Land. MCA cooling found in the Ross Ice Shelf region and probably in the Weddell Sea. Spatial distribution of MCA cooling and warming follows modern dipole patterns. Main drivers Southern Annular Mode (SAM) and El Niño-Southern Oscillation (ENSO). Abstract The Medieval Climate Anomaly (MCA) is a well-recognized climate perturbation in many parts of the world, with a core period of 1000–1200 CE. Here we are mapping the MCA across the Antarctic region based on the analysis of published palaeotemperature proxy data from 60 sites. In addition to the conventionally used ice core data, we are integrating temperature proxy records from marine and terrestrial sediment cores as well as radiocarbon ages of glacier moraines and elephant seal colonies. A generally warm MCA compared to the subsequent Little Ice Age (LIA) was found for the Subantarctic Islands south of the Antarctic Convergence, the Antarctic Peninsula, Victoria Land and central West Antarctica. A somewhat less clear MCA warm signal was detected for the majority of East Antarctica. MCA cooling occurred in the Ross Ice Shelf region, and probably in the Weddell Sea and on Filchner-Ronne Ice Shelf. Spatial distribution of MCA cooling and warming follows modern dipole patterns, as reflected by areas of opposing temperature trends. Main drivers of the multi-centennial scale climate variability appear to be the Southern Annular Mode (SAM) and El Niño-Southern Oscillation (ENSO) which are linked to solar activity changes by nonlinear dynamics. This paywalled article appears on the Palaeogeography, Palaeoclimatology and Palaeoecology website at https://www.sciencedirect.com/science/article/pii/S0031018219303190?dgcid=author

Medieval Warm Period Now Confirmed In Southern Hemisphere On All Four Continents

July 7, 2019

https://notrickszone.com/2019/07/06/medieval-climate-anomaly-now-confirmed-in-southern-hemisphere-on-all-four-continents/ By P Gosselin on 6. July 2019 In Medieval times, the penguins had it nice and warm By Die kalte Sonne (German text translated in the English by P Gosselin) For a long time it has been said that the Medieval Warm Period was a purely North Atlantic phenomenon. This has proved to be wrong. On 29 June 2019, a paper by Lüning et al. 2019 on the Medieval Warm Period in Antarctica appeared in the trade journal Palaeogeography, Palaeoclimatology, Palaeoecology. Here is the abstract: The Medieval Climate Anomaly in Antarctica The Medieval Climate Anomaly (MCA) is a well-recognized climate perturbation in many parts of the world, with a core period of 1000–1200 CE. Here we are mapping the MCA across the Antarctic region based on the analysis of published palaeotemperature proxy data from 60 sites. In addition to the conventionally used ice core data, we are integrating temperature proxy records from marine and terrestrial sediment cores as well as radiocarbon ages of glacier moraines and elephant seal colonies. A generally warm MCA compared to the subsequent Little Ice Age (LIA) was found for the Subantarctic Islands south of the Antarctic Convergence, the Antarctic Peninsula, Victoria Land and central West Antarctica. A somewhat less clear MCA warm signal was detected for the majority of East Antarctica. MCA cooling occurred in the Ross Ice Shelf region, and probably in the Weddell Sea and on Filchner-Ronne Ice Shelf. Spatial distribution of MCA cooling and warming follows modern dipole patterns, as reflected by areas of opposing temperature trends. Main drivers of the multi-centennial scale climate variability appear to be the Southern Annular Mode (SAM) and El Niño-Southern Oscillation (ENSO) which are linked to solar activity changes by nonlinear dynamics. With the publication of this paper, the Medieval Climate Anomaly (MCA) has now been confirmed on all four continents of the southern hemisphere. While the largest part of the southern hemisphere apparently experienced a warm phase during the MCA, there were also isolated areas that cooled down. To the latter regions belong, for example, coasts, where cold water from the depth rose increasingly. In other areas so-called climate seesaws or dipoles were active, as we know them from today’s climate. One end of the “seesaw” heats up, the other end cools down. Another result of the studies is that the medieval climate history of huge areas in the southern hemisphere is simply unknown. A task force urgently needs to be set up to fill in this climatic “empty space” with information on pre-industrial temperature development. This information is urgently needed to calibrate the climate models on the basis of which far-reaching socio-political planning is currently taking place. What follows are publications on the Medieval Period climate of the southern hemisphere as an overview: Lüning, S., M. Gałka, F. Vahrenholt (2019): The Medieval Climate Anomaly in Antarctica. Palaeogeogr., Palaeoclimatol., Palaeoecol., doi: 10.1016/j.palaeo.2019.109251 Lüning, S., M. Gałka, F. García-Rodríguez, F. Vahrenholt (2019): The Medieval Climate Anomaly in Oceania. Environmental Reviews, online Just-IN, doi: 10.1139/er-2019-0012 Lüning, S., M. Gałka, F. P. Bamonte, F. García-Rodríguez, F. Vahrenholt (2019): The Medieval Climate Anomaly in South America. Quaternary International, 508: 70-87. doi: 10.1016/j.quaint.2018.10.041. Lüning, S., M. Gałka, F. Vahrenholt (2017): Warming and cooling: The Medieval Climate Anomaly in Africa and Arabia. Paleoceanography 32 (11): 1219-1235, doi: 10.1002/2017PA003237. All supporters of the studies once again receive our deepest thanks. At the start of the project, a devoted crowdfunding team gave the studies a strong boost.

Physicist calls NYC’s climate inspired ban on hot dogs & processed meats ‘insane, unscientific, medieval ritual’

April 26, 2019

Former Harvard University Physicist Dr. Lubos Motl: Excerpt: Newyorkers and others should learn quite a lesson from de Blasio’s steps and those people who are willing to believe that “one helps the climate or the planet” by a crazy policy such as the ban of processed meat in the whole city should be classified as politically immature – because they are – and stripped of their voting rights (and surely the right to run for the office). The effect of the New York ban on the temperature of Earth is again in tens of microkelvins – it’s totally negligible. Will you seriously cripple the quality of your life because of some microkelvins, especially if you know that the weather will be infinitesimally better if you eat some of the processed food? If there isn’t an agreement about such medical conditions for the voting and political rights, I think it will be necessary to separate the people like Bill de Blasio from the sane people who understand why such bans are insane, unscientific, medieval rituals. The likes of de Blasio and his voters may live in their desired paradise without hot dogs but they shouldn’t have the power to restrict the basic rights of sane people at the same moment. The degree of insanity that these people are spreading in the world – and their impact (the New York City is more than just an average village) – are reaching truly dangerous proportions.

Newsweek features Morano – Mag. agrees with Morano’s claims on UN Paris pact! FOX NEWS GUEST MORANO SAYS ADDRESSING CLIMATE THROUGH PARIS AGREEMENT ARE ‘MEDIEVAL WITCHCRAFT’

February 12, 2019

Watch Full Fox & Friends Segment here: Morano point #1 on Fox & Friends Feb. 12, 2019: “The authors of this two degree target actually admit it was, quote, pulled from thin air, the scientists in the United Nations admit this.” See: Book reveals UN’s goal of ‘2 degree’ limit of ‘global warming’ has no scientific basis – ‘Pulled out of thin air’ Newsweek response: “I think that the two degree target was chosen more for political reasons than for true scientific reasons,” Columbia University professor Scott Barrett, who served on the U.N. Climate Panel, told PBS NewsHour in 2015. “The idea was to — if countries could agree on a collective target, that that would mobilize the action needed to get the whole world to act together.” Morano point #2 on Fox & Friends Feb. 12, 2019: “So — and then even The Washington Post has acknowledged that. (See: WaPo: ‘The surge of optimism that came with UN Paris pact has faded – ‘Promises that are widely acknowledged to be too weak to begin with’) Even if you’re afraid of global warming, the U.N. Paris Agreement would basically do nothing, has no impact on the climate. This is medieval witchcraft to think that we can all come together with some treaty, make a bunch of pledges, and have a temperature a hundred years that’s different.” See: Statisician Blasts UN Paris Treaty’s $100 Trillion Price Tag For No Temp Impact: ‘You won’t be able to measure it in 100 years’ Newsweek: Critics of the Paris Agreement have noted Morano’s argument about the ability for the Paris Agreement to enact change. After the announcement of the international accord — which Trump withdrew from in 2017 — critics argued that it lacked legal enforceability. In December, nations at the COP24 conference agreed on a set of rules detailing how countries will track emissions. But experts still expressed concern about the pace of progress. “My biggest concern is that the UN talks failed to align ambitions with science,” Johan Rockstrom, the director designate at the Potsdam Institute for Climate Impact Research, told The Guardian. https://www.newsweek.com/efforts-address-climate-change-are-medieval-witchcraft-fox-guest-1327836 BY DANIEL MORITZ-RABSON ON 2/12/19 AT 10:54 AM Efforts to address climate change with the Paris Agreement amount to “medieval witchcraft” a guest on Fox & Friends said Tuesday. “It’s been called the most expensive treaty in world history with a price tag of upwards of $100 trillion, a global cost of $1 to $2 trillion annually, and, again, you mentioned this two degree thing, and I actually point out this was — The authors of this two degree target actually admit it was, quote, pulled from thin air, the scientists in the United Nations admit this,” Marc Morano, director of communications for nonprofit Committee for a Constructive Tomorrow, said while appearing on the show. “So — and then even The Washington Post has acknowledged that, even if you’re afraid of global warming, the U.N. Paris Agreement would basically do nothing, has no impact on the climate. This is medieval witchcraft to think that we can all come together with some treaty, make a bunch of pledges, and have a temperature a hundred years that’s different.” Media Matters described Morano as a “climate denier.” “I think that the two degree target was chosen more for political reasons than for true scientific reasons,” Columbia University professor Scott Barrett, who served on the U.N. Climate Panel, told PBS NewsHour in 2015. “The idea was to — if countries could agree on a collective target, that that would mobilize the action needed to get the whole world to act together.” Studies have shown that if the planet warms 2 degrees Celsius above pre-industrial levels, the impacts will be devastating. A landmark report from the UN Intergovernmental Panel on Climate Change, which was released in October, warned that a global temperature increase above 1.5 degrees Celsius will exacerbate the danger of climate-driven disasters. Vox noted that an increase of 2 degrees Celsius will lead to increased heat waves, decreased freshwater availability, rising sea levels and coral bleaching. Despite the scientific evidence behind climate change and consensus among the scientific community, skeptics have appeared on Fox News and CNN to dispute the anthropogenic trend. Critics of the Paris Agreement have noted Morano’s argument about the ability for the Paris Agreement to enact change. After the announcement of the international accord — which Trump withdrew from in 2017 — critics argued that it lacked legal enforceability. In December, nations at the COP24 conference agreed on a set of rules detailing how countries will track emissions. But experts still expressed concern about the pace of progress. “My biggest concern is that the UN talks failed to align ambitions with science,” Johan Rockstrom, the director designate at the Potsdam Institute for Climate Impact Research, told The Guardian. “We continue to follow a path that will take us to a very dangerous 3-4C warmer world within this century. Extreme weather events hit people across the planet already, at only 1C of warming.”

Warmists upset: ‘Climate denier’ Morano on Fox & Friends: International efforts to address climate change are ‘medieval witchcraft”

February 12, 2019

MEDIA MATTERS STAFF https://www.mediamatters.org/video/2019/02/12/climate-denier-fox-friends-international-efforts-address-climate-change-are-medieval-witchcraft/222835 MARC MORANO (CLIMATEDEPOT.COM): It’s been called the most expensive treaty in world history with a price tag of upwards of $100 trillion, a global cost of $1 to $2 trillion annually, and, again, you mentioned this two degree thing, and I actually point out this was — the authors of this two degrees target actually admit it was, quote, pulled from thin air, the scientists in the United Nations admit this. So — and then even The Washington Post has acknowledged that, even if you’re afraid of global warning, the U.N. Paris Agreement would basically do nothing, has no impact on the climate. This is medieval witchcraft to think that we can all come together with some treaty, make a bunch of pledges, and have a temperature a hundred years that’s different.

Watch: Morano on Canadian TV: ‘Medieval clerics’ of green movement impose ‘sin tax’ on meat

January 13, 2019

https://www.therebel.media/medieval-clerics-of-green-movement-impose-sin-tax-on-meat-consumption On Friday’s episode of The Ezra Levant Show, I was joined by Marc Morano of ClimateDepot.com to talk about some breaking “global warming” stories including a green MP in the UK calling on Parliament to impose a tax on meat to cut greenhouse gas emissions and reduce climate change. The idea of going after meat consumption in the name of the planet has been around for a while and started as a social movement with some even pushing the idea of eating bugs as a source of “earth-friendly” protein. Despite contradictory studies on the question, the general consensus among the climate activists is that meat-eating is bad, agriculture is bad – let’s tax it to death. Watch as Marc explains how veganism has become the new religionfor urban atheists who want to impose their green ideology on us like medieval clerics imposing austere lifestyles on the people in service of the earth. SHARE THIS ON FACEBOOK

Climate scientist retires, then declares ‘I am a skeptic’ – Offers to debate – Rejects ‘denier’ label: ‘We don’t live in medieval times’

January 10, 2019

https://www.washingtontimes.com/news/2019/jan/2/the-overblown-and-misleading-issue-of-global-warmi/ The overblown and misleading issue of global warming By Anastasios Tsonis – January 2, 2019 Very often, when I talk to the public or the media about global warming (a low-frequency positive trend in global temperature in the last 120 years or so), they ask me the unfortunate question if I “believe” in global warming. And I say “unfortunate” because when we are dealing with a scientific problem “believing” has no place. In science, we either prove or disprove. We “believe” only when we cannot possibly prove a truth. For example, we may “believe” in reincarnation or an afterlife but we cannot prove either. One may argue that when we are dealing with a scientific problem, such as global warming, for which we cannot obtain unquestionable experimental confirmation as to what is causing it (for the simple reason that we cannot repeat this experiment; we only have one realization of climate evolution), we may form an opinion based on the existing scientific evidence in hand, current knowledge, possible theories and hypotheses. But we should be skeptical of claims that the science of a complicated and unpredictable system is settled. Nobody argues that the temperature of the planet is not increasing in the last 120 years or so. Yes, the temperature is increasing overall. But there are a lot of questions regarding why that is. In the current state of affairs regarding global warming, opinion is divided into two major factions. A large portion of climate scientists argues that most, if not all, of the recent warming is due to anthropogenic effects, which originate largely from carbon dioxide emissions from the burning of fossil fuels. Another portion is on the other extreme: Those who argue that humans have nothing to do with global warming and that all this fuss is a conspiracy to bring the industrial world down. The latter group calls the former group “the catastrophists” or “the alarmists,” whereas the former group calls the latter group “the deniers.” This childish division is complemented by another group, the “skeptics,” which includes those like me who question the extreme beliefs and try to look at all scientific evidence before we form an opinion (by the way, the former group also considers skeptics to be deniers). In the realm of deniers, skeptics and believers, science has been compromised. I usually don’t bother with pseudo-scientists, media and ignorant people abusing the freedom of the Internet by writing and posting nonsense comments. But I have grown wary of what is going on with the debate on the overblown and misdirected issue of global warming — a case in point being “Meet the Press” host Chuck Todd saying he will no longer give time to global warming “deniers” and also that the “science is settled.” The fact that scientists who show results not aligned with the mainstream are labeled deniers is the backward mentality. We don’t live in the medieval times, when Galileo had to admit to something that he knew was wrong to save his life. Science is all about proving, not believing. In that regard, I am a skeptic not just about global warming but also about many other aspects of science. All scientists should be skeptics. Climate is too complicated to attribute its variability to one cause. We first need to understand the natural climate variability (which we clearly don’t; I can debate anybody on this issue). Only then we can assess the magnitude and reasons of climate change. Science would have never advanced if it were not for the skeptics. All model projections made for the 21st century failed to predict the slowdown of the planet’s warming despite the fact that carbon dioxide emissions kept on increasing. Science is never settled. If science were settled, then we should pack things up and go home. My research over the years is focused on climate variability and climate dynamics. It is my educated opinion that many forces have shaped global temperature variation. Human activity, the oceans, extraterrestrial forces (solar activity and cosmic rays) and other factors are all in the mix. It may very well be that human activity is the primary reason, but having no strong evidence of the actual percent effect of these three major players, I will attribute 1/3 to each one of them. Two final points. First, all the interactions of humans with the environment are part of our technological evolution. During this evolution, we could not go directly from living in the dark ages to a clean energy technology. There was no other way but to use fossil fuels and other pollution-producing agents. Is this enough to ruin the planet by altering the climate system, a system that has undergone major changes throughout the ages? Second, while we should try our best to take care of our planet, global warming is not the only urgent planetary emergency. Overpopulation, poverty, infectious diseases and the effect of globalization in spreading them, the water crisis, energy and food availability and safety, political instability and terrorism, the global economy, even cyber security, are far more urgent problems with potentially catastrophic results for humanity. • Anastasios Tsonis is emeritus distinguished professor at the University of Wisconsin-Milwaukee. He is the author of more than 130 peer reviewed papers and nine books.

New Study: Medieval Warm Period Not Limited To North Atlantic, But Occurred In South America As Well

November 5, 2018

http://notrickszone.com/2018/11/03/new-study-medieval-warm-period-not-limited-to-north-atlantic-but-occurred-in-south-america-as-well/ By P Gosselin Global warming alarmist scientists like claiming that the well documented Medieval Warm Period (MWP) was merely a regional phenomenon, and not global. However a new publication by Lüning et al adds yet another study that shows the warm period from 1000 years ago was indeed global. ================================ Image source: here. Preindustrial climate change in South America: the Middle Age was warm, glaciers shrank By Dr. Sebastian Lüning and Prof. Fritz Vahrenholt (German text translated/edited by P Gosselin) The climate of the Middle Ages is still a mystery. In many parts of the world a warming period occurred, which can still not be satisfactorily simulated by the current climate models. The problem: natural climate factors play almost no role in the models. It is therefore all the more important to first carry out a proper mapping of the climate for this important period. A research group led by Sebastian Lüning has presented an overview of the medieval climate in South America and now appears in the journal Quaternary International. Here the scientists summarized a large number of case studies of the entire continent. The climate archives included pollen surveys in lake sediments of the Andes, which documented the rise and drop of the tree line. Other studies reconstructed the oscillating shrinking and growth of Andean glaciers or dealt with tree rings. As a result, Lüning and his team found that the vast majority of the 76 individual studies indicate warming during the early 2nd millennium. The Medieval Warm Period was also strongly represented in South America. Exceptions were some coastal waters, where increased buoyancy of cold water led to a cooling. What follows is the abstract: The Medieval Climate Anomaly in South America The Medieval Climate Anomaly (MCA) is a climatic perturbation with a core period of 1000-1200 AD that is well-recognized in the Northern Hemisphere (NH). Its existence in the Southern Hemisphere (SH) and the level of synchronicity with the NH is still a matter of debate. Here we present a palaeotemperature synthesis for South America encompassing the past 1500 years based on multiproxy data from 76 published land and marine sites. The data sets have been thoroughly graphically correlated and the MCA trends palaeoclimatologically mapped. The vast majority of all South American land sites suggest a warm MCA. Andean vegetation zones moved upslope, glaciers retreated, biological productivity in high altitude lakes increased, the duration of cold season ice cover on Andean lakes shortened, and trees produced thicker annual rings. Similar MCA warming occurred in coastal seas, except in the year-round upwelling zones of Peru, northern Chile and Cabo Frio (Brazil) where upwelling processes intensified during the MCA due to changes in winds and ocean currents. MCA warming in South America and the NH appears to have occurred largely synchronous, probably reaching comparable intensities. Future studies will have to address major MCA data gaps that still exist outside the Andes in the central and eastern parts of the continent. The most likely key drivers for the medieval climate change are multi-centennial Pacific and Atlantic ocean cycles, probably linked to solar forcing.” The mapping of the South American climate is part of a wider global study on medieval climate change. The project was kindly supported by crowdfunding during the launch phase. Here all published climate reconstructions are first collected on a Google Map and then plotted and compared in detail. In the appendix of the regional syntheses, each individual location is precisely evaluated and the resulting climate changes are discussed. The studies benefit from the great willingness by a large number of paleoclimatologists to cooperate and who readily provide their data for evaluation and discuss technical questions with the authors of the syntheses. Great thanks to everyone involved!

Yet another new study finds global Medieval Warm Period: S. America and N. Hemisphere medieval warming ‘occurred largely synchronous, probably reaching comparable intensities’

November 2, 2018

https://www.sciencedirect.com/science/article/pii/S1040618218308322 Quaternary International The Medieval Climate Anomaly in South America Author links open overlay panelSebastianLüningaMariuszGałkabFlorencia PaulaBamontecFelipe GarcíaRodríguezd1FritzVahrenholte Show more https://doi.org/10.1016/j.quaint.2018.10.041Get rights and content Abstract The Medieval Climate Anomaly (MCA) is a climatic perturbation with a core period of 1000-1200 AD that is well-recognized in the Northern Hemisphere (NH). Its existence in the Southern Hemisphere (SH) and the level of synchronicity with the NH is still a matter of debate. Here we present a palaeotemperature synthesis for South America encompassing the past 1500 years based on multiproxy data from 76 published land and marine sites. The data sets have been thoroughly graphically correlated and the MCA trends palaeoclimatologically mapped. The vast majority of all South American land sites suggest a warm MCA. Andean vegetation zones moved upslope, glaciers retreated, biological productivity in high altitude lakes increased, the duration of cold season ice cover on Andean lakes shortened, and trees produced thicker annual rings. Similar MCA warming occurred in coastal seas, except in the year-round upwelling zones of Peru, northern Chile and Cabo Frio (Brazil) where upwelling processes intensified during the MCA due to changes in winds and ocean currents. MCA warming in South America and the NH appears to have occurred largely synchronous, probably reaching comparable intensities. Future studies will have to address major MCA data gaps that still exist outside the Andes in the central and eastern parts of the continent. The most likely key drivers for the medieval climate change are multi-centennial Pacific and Atlantic ocean cycles, probably linked to solar forcing. Keywords Climate changeLate HoloceneLittle Ice AgeTemperature reconstructionsPalaeoclimatologyEl Niño-Southern OscillationMedieval Warm PeriodSouthern Hemisphere 1 Present address: Programa de Pós-Graduação em Oceanografia Física, Química e Geológica, Instituto de Oceanografia, Universidade Federal do Rio Grande, Av. Itália, km 8, Cx.P. 474, 96201-900, Rio Grande, RS, Brazil.

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