In South America, the Medieval Warm Period—often called the Medieval Climate Anomaly (MCA), spanned roughly from 900 to 1350 CE.

It brought widespread land warming, retreating Andean glaciers, and shifted ecological zones, though coastal upwelling intensified in specific Pacific and Atlantic zones due to altered wind and ocean current patterns- Environmental and Climatic Effects

Glacial Retreat: High-altitude ice fields and glaciers in the Andes shrank significantly as temperatures rose.

Vegetation Shifts: Andean plant and tree lines moved higher up mountain slopes in response to the warmth.

Lake Productivity: High-elevation lakes experienced shorter periods of cold-season ice cover and increased biological activity.

Tree Ring Data: Trees across southern land sites produced wider, thicker annual growth rings.

The description aligns with paleoclimate evidence for the Medieval Climate Anomaly (MCA, roughly 900–1350 CE) in South America, though regional patterns were not uniform.

Key points from multiproxy records (glacier, lake, pollen, tree-ring, and marine data):

• Glacial retreat: Andean glaciers and high-altitude ice fields generally advanced less or retreated relative to later Little Ice Age conditions. Temperature reconstructions and glacial geomorphology indicate warmer conditions at elevation during much of the MCA, consistent with reduced ice extent.
• Vegetation and ecological shifts: Pollen and macrofossil records show upward migration of Andean treelines and plant zones in response to higher temperatures and, in some areas, altered precipitation. High-elevation lakes often record reduced seasonal ice cover and higher biological productivity (e.g., increased diatom or chironomid indicators).
• Tree rings: Southern South American chronologies (especially Patagonia and parts of the southern Andes) frequently show wider rings during MCA intervals, reflecting favorable growing conditions (warmer temperatures and/or adequate moisture in those sites).
• Oceanic/coastal contrasts: While continental interiors and highlands tended to warm, some Pacific (and to a lesser extent Atlantic) coastal and upwelling zones experienced intensified or altered upwelling linked to changes in wind patterns and the intertropical convergence zone / South Pacific subtropical high. This produced cooler surface waters or higher productivity in specific nearshore areas even as adjacent land warmed—an example of the spatially heterogeneous “anomaly” rather than a globally uniform warm period.

Overall, the MCA in South America is better characterized as a period of regionally coherent but not identical climate shifts (warmer highlands, glacier retreat, ecological reorganization, and variable hydroclimate) rather than a simple continent-wide uniform warming.

Proxy coverage remains denser in the Andes and southern latitudes than in the tropical lowlands or far northern Andes, so reconstructions continue to be refined.

This is the 2019 paper “The Medieval Climate Anomaly in South America” by Sebastian Lüning, Mariusz Gałka, Florencia Paula Bamonte, Felipe García Rodríguez, and Fritz Vahrenholt, published in Quaternary International (Volume 508, pages 70–87).

Core findings

• Scope: Multiproxy palaeotemperature synthesis for the past ~1500 years using data from 76 published land and marine sites across South America. The authors graphically correlated the records and mapped MCA trends.
• Timing: Core period of the MCA given as ~1000–1200 CE (within the broader ~900–1350 CE window sometimes used).
• Land sites: The large majority indicate a warm MCA. Evidence includes:
  • Andean vegetation zones / tree lines shifting upslope.
  • Glacier retreat in the Andes.
  • Increased biological productivity in high-altitude lakes.
  • Shorter cold-season ice cover on Andean lakes.
  • Wider/thicker annual tree rings at southern land sites.
• Marine/coastal sites: Warming in most coastal seas, except in year-round upwelling zones off Peru, northern Chile, and Cabo Frio (Brazil). There, upwelling intensified due to changes in winds and ocean currents.
• Hemispheric comparison: MCA warming in South America appears largely synchronous with the Northern Hemisphere and of broadly comparable intensity.
• Data gaps: Sparse coverage outside the Andes (central and eastern parts of the continent).
• Proposed drivers: Multi-centennial Pacific and Atlantic Ocean cycles, possibly linked to solar forcing.

The paper reviews earlier reconstructions (e.g., Neukom et al. 2011, PAGES 2k) that had limited MCA-era proxies for the region and aims to provide a more comprehensive spatial picture.

A freely accessible version (author manuscript / open manuscript) is available via repositories such as Archimer (Ifremer).

This ResearchGate page is for the exact same paper

Lüning, S., Gałka, M., Bamonte, F.P., García Rodríguez, F., & Vahrenholt, F. (2019).
“The Medieval Climate Anomaly in South America.”
Quaternary International, 508, 70–87.
DOI: 10.1016/j.quaint.2018.10.041It is listed there as a “Request PDF” entry (common on ResearchGate when the full text is not openly uploaded by the authors). The abstract and core findings match the ScienceDirect version and the author manuscript available elsewhere.

Free full-text optionsA freely downloadable author manuscript / open version is available here:
https://archimer.ifremer.fr/doc/00497/60854/101604.pdf

That PDF contains the complete text, figures, and supporting information references.

In South America (and more broadly), the Medieval Climate Anomaly (MCA) and Little Ice Age (LIA) represent contrasting multi- centennial climate regimes during the last millennium.

The comparison below draws primarily from the Lüning et al. (2019) multiproxy synthesis of 76 South American sites, supplemented by related paleoclimate literature.

Timing

• MCA: Core period roughly 1000–1200 CE (broader window often cited as ~900–1350 CE).
• LIA: Roughly 1300/1400–1850 CE (peak cold phases often mid-17th to early 18th century in the Andes; some regions show maximum glacier extent later, into the early 19th century).

The transition is marked by the first notable Andean glacier advances around 1200–1350 CE, ending the warmer medieval conditions.

Temperature

• MCA: Predominantly warm across most South American land sites. Evidence includes upslope shifts of Andean vegetation/tree lines, increased high-elevation lake productivity, shorter cold-season lake ice cover, and wider tree rings in southern sites. Warming was largely synchronous with the Northern Hemisphere and of broadly comparable intensity in many reconstructions. Coastal seas also warmed except in specific year-round upwelling zones (Peru, northern Chile, Cabo Frio/Brazil), where intensified upwelling produced cooler surface waters.
• LIA: Predominantly cooler. Andean glaciers advanced to their furthest down-valley positions in many areas (especially mid-17th–early 18th century, or later in northern Patagonia). It ranks among the coldest phases of the past 10,000 years globally (alongside the 8.2 ka event). Modern glacier retreat largely began after the LIA peak.

Quantitative estimates vary by region and proxy, but southern South American summer temperature reconstructions (e.g., Neukom et al.) show the MCA warmer than the LIA by several tenths of a degree on average (locally up to ~1°C or more in some areas), though early reconstructions had limited MCA-era data.

Glaciers and cryosphere

• MCA: Significant retreat or reduced extent of high-altitude Andean ice fields and glaciers.
• LIA: Major advances; many glaciers reached their Holocene maxima or near-maxima. Venezuela has since lost nearly all its glaciers in the post- LIA warming.

Hydroclimate and ecosystems

• Patterns were regionally variable (not a simple uniform “wet” or “dry” continent-wide shift).
• MCA: Often associated with altered monsoon strength (frequently weaker South American Summer Monsoon in parts of the tropics/subtropics in various proxy syntheses), shifts in the Intertropical Convergence Zone (ITCZ), and vegetation zone changes tied to warmth. Lake and pollen records reflect the warmer conditions.
• LIA: Frequently wetter conditions in parts of the tropical Andes and monsoon-influenced regions (stronger monsoon in many records), with cooler temperatures reducing evaporation and increasing effective moisture in some highland areas. Glacier advances reflect both cooling and, in places, increased precipitation.

Ocean and atmospheric circulation

• MCA: Changes in winds and ocean currents intensified upwelling in specific Pacific and Atlantic zones (counteracting land/coastal warming locally). Multi-centennial Pacific and Atlantic Ocean cycles (possibly solar-linked) are proposed as key drivers.
• LIA: Different boundary conditions, often linked to a more southward ITCZ position in some interpretations, altered ENSO- like states, and stronger monsoon circulation in parts of the continent.

Data density is highest in the Andes and southern latitudes; central/eastern South America has larger gaps.

Both periods show spatial heterogeneity—neither was a simple, uniform global temperature anomaly.

Hydroclimate responses (monsoon, precipitation) can diverge from pure temperature signals and differ between northern and southern tropical Andes or Atlantic vs. Pacific sectors.

The MCA provides the most recent pre-industrial multi-centennial warm phase for comparison with the Current Warm Period.

The LIA represents the coldest multi-centennial interval of the late Holocene in many records.

The shift from MCA warmth/glacier retreat to LIA cooling/glacier advance is one of the clearest features in Andean glacial histories and aligns broadly with Northern Hemisphere patterns, though amplitudes and exact phasing can differ by region and proxy.

Several studies published after the 2019 Lüning et al. paper address the Medieval Climate Anomaly (MCA) versus the Little Ice Age (LIA) in South America.

They generally support a warmer MCA relative to a cooler LIA, while adding more detail on hydroclimate (precipitation/monsoon), regional differences, and glacier behavior.

Here are the most relevant ones:

Choblet et al. (2024) – Climate of the Past
Continental-scale hydroclimatic reconstruction for the past 2,000 years using multi-timescale paleoclimate data assimilation (proxies + isotope-enabled models).

• Early MCA (~600–900 CE): drier and warmer.
• LIA (~1500–1850 CE): wetter and colder.
• Patterns are not uniform — northeastern Brazil and the Southern Cone often deviate from the continental average. Anomalies appear stronger than in some earlier reconstructions, partly due to inclusion of speleothem data.

Bird et al. (2024) – Journal of Geophysical Research: Atmospheres
Focus on tropical Andean hydroclimate using new lake records from the eastern Colombian Andes plus existing circum-Andean proxies.

• MCA (defined ~950–1150 CE): generally warmer and drier conditions across the tropical Andes (linked to a northward-shifted ITCZ, reduced precipitation, and higher evaporation in the north; also reduced precipitation in the south).
• LIA (~1300–1850 CE): cooler and wetter overall (higher effective moisture). In the northern Andes, lower precipitation was offset by reduced evaporation from cooling; in the southern tropical Andes, a southward ITCZ strengthened precipitation.
• Responses were largely synchronous and in phase across the tropical Andes (challenging some earlier ideas of strong north–south opposition).

Glacier-focused work

• Multiple post-2019 studies document substantial Andean glacier retreat since the LIA maximum (roughly 1400–1850 CE), with accelerated losses in recent decades. Tropical Andes glaciers show particularly large relative area losses (median ~56% from LIA extent to ~2000 in one synthesis).
• Pre-industrial variability includes MCA-related retreat followed by LIA advances, though exact timing and magnitude vary regionally; some authors note that modern retreat exceeds typical pre-industrial fluctuations.

Other notable contributions

• Ozán et al. (2022) – Review of Patagonian paleoenvironmental records: most high-quality sites indicate dry and/or warm conditions during the MCA core (~800–1200 CE), with implications for past human societies.
• Studies of the South American Summer Monsoon (building on earlier work) continue to show a tendency toward a weaker monsoon during the MCA and stronger monsoon during the LIA in many tropical/subtropical records, though spatial details and exact phasing differ.
• Model and proxy work on the Atlantic Multidecadal Oscillation (AMO) explores its possible role in the MCA-to-LIA transition and isotopic fingerprints over South America.

Overall synthesis from post-2019 work

The broad temperature contrast (MCA warmer than LIA) remains consistent with Lüning et al. (2019). Newer research emphasizes:

• Stronger focus on hydroclimate (often drier MCA / wetter LIA in monsoon-influenced regions).
• Greater appreciation of regional heterogeneity (e.g., exceptions in NE Brazil, Southern Cone, or local Andean valleys).
• Improved integration of speleothems, lake sediments, and data-assimilation techniques.
• Glacier records confirming LIA advances and subsequent (accelerating) retreat.

Data gaps outside the Andes persist, and definitions of exact MCA/LIA boundaries still vary slightly between studies.

No single post-2019 paper has fully superseded the 76-site temperature mapping of Lüning et al., but the newer work significantly expands the hydroclimate and process-level picture.