Medieval Warm Epoch Research Articles

Holocene human adaptation in the Namib Desert: A model based on the concept of Holling's loop

Climatic amelioration during the mid-Holocene Optimum is associated with hunter-gatherer occupation of remote sites in the Namib Desert. Subsequent changes in late Holocene site distribution suggest there were alternative responses to increasing aridity during this period. Abandonment or episodic occupation is evident in some areas, while others show an emphasis on mountain refugia and resource anomalies. Specialized coping strategies developed during this time allowed a broad re-occupation of the desert when conditions improved briefly during the Medieval Warm Epoch. Successive patterns of settlement and subsistence in the Namib Desert Holocene sequence exemplify the four moments of Holling's adaptive cycle.

Settlement patterns as indicators of water level rising? Case study on the wetlands of the Great Hungarian Plain

The paper focuses on changes in settlement patterns on the frontier zones of wetlands and areas suitable for settling in the Great Hungarian Plain, Central Europe. Based on the statistical analysis of archaeological site elevations in a 4.128 km² lowland landscape, it is demonstrated that archaeological sites of the Árpád Period (AD 970–1300) were situated significantly (p = 0.01; n = 427) lower than those of the late medieval period (AD 1300–1540). Statistical results suggest that rising water levels are likely to have influenced the migration and transformation in settlement patterns from the Medieval Warm Epoch (mid-10th – mid-13th century) to the first part of the Little Ice Age (mid-13th century – mid-16th century). Zonal analysis also revealed close connections between flood-prone geomorphological features and spatiotemporal variations of settlement patterns during the medieval climate change. With regard to the lowland character of the extensive study area, its relatively high flood vulnerability and the numerous analogies from Europe and the Carpathian Basin, only one out of the multitude of factors influencing site selection, water level changes can be interpreted as a rational explanation for the vertical displacement of the settlement pattern.

Climate change during the Iron Age in the Shashe-Limpopo Basin, southern Africa

Recent research refines previous interpretations about the role of climatic factors in the development of Mapungubwe. First, the Medieval Warm Epoch started at about AD 1000, rather than 900. At about AD 900, Zhizo people moved into the Shashe-Limpopo Basin, most likely to hunt elephants for the East Coast trade. Secondly, a dry period at about AD 1200–1250 affected farming societies over a wide area. In the Basin, multiple rainmaking episodes occurred at this time. A similar situation took place around Makapansgat and at Great Zimbabwe. Thirdly, Mapungubwe was probably abandoned in AD 1300 because of cooler and drier conditions. At this time, it would have been impossible to maintain floodplain agriculture at the intensity necessary to support the large population. Agricultural failures probably undermined political authority, contributing to Mapungubwe's abandonment and shift in power to Great Zimbabwe. This detailed sequence challenges the re-calibrated climatic series from Makapansgat.

Magnetic record associated with tree ring density: Possible climate proxy

A magnetic signature of tree rings was tested as a potential paleo-climatic indicator. We examined wood from sequoia tree, located in Mountain Home State Forest, California, whose tree ring record spans over the period 600 – 1700 A.D. We measured low and high-field magnetic susceptibility, the natural remanent magnetization (NRM), saturation isothermal remanent magnetization (SIRM), and stability against thermal and alternating field (AF) demagnetization. Magnetic investigation of the 200 mm long sequoia material suggests that magnetic efficiency of natural remanence may be a sensitive paleoclimate indicator because it is substantially higher (in average >1%) during the Medieval Warm Epoch (700–1300 A.D.) than during the Little Ice Age (1300–1850 A.D.) where it is <1%. Diamagnetic behavior has been noted to be prevalent in regions with higher tree ring density. The mineralogical nature of the remanence carrier was not directly detected but maghemite is suggested due to low coercivity and absence of Verwey transition. Tree ring density, along with the wood's magnetic remanence efficiency, records the Little Ice Age (LIA) well documented in Europe. Such a record suggests that the European LIA was a global phenomenon. Magnetic analysis of the thermal stability reveals the blocking temperatures near 200 degree C. This phenomenon suggests that the remanent component in this tree may be thermal in origin and was controlled by local thermal condition.

Warm summers and ion concentrations in snow: comparison of present day with Medieval Warm Epoch from snow pits and an ice core from Lomonosovfonna, Svalbard

Snow pits sampled during two consecutive years (2001, 2002) at the summit of Lomonosovfonna ice cap in central Spitsbergen, Svalbard, showed that ion concentrations were spatially homogeneous. The snowpack on Lomonosovfonna shows no evidence of aerosol deposition from Arctic haze, in contrast to Holtedahlfonna (a glacier at a similar altitude in northern Spitsbergen) where there is a clear signature. In common with many other ice caps in the Arctic, Lomonosovfonna experiences periodic melting, and the deepest of the snow pits contained a record of one exceptionally warm (2001) and one long summer (2000). The most easily eluted species are nitrate and the divalent ions. Very low ion concentrations and high values of a melt indicator log([Na+]/[Mg2+]) were a result of either deep percolation or runoff of ions during melting. Comparing the snow-pit record with the ion record of more than 800 years from an ice core drilled on Lomonosovfonna in 1997 reveals some layers with similar composition to those that suffered significant melting in the snowpack: a few years in the 20th century and around AD 1750, and all of the core from before AD 1200 show unusually heavy melting.

Climatic and environmental changes over the last millennium recorded in the Malan ice core from the northern Tibetan Plateau

In this paper, climatic and environmental changes were reconstructed since 1129A.D. based on the Malan ice core from Hol Xil, the northern Tibetan Plateau. The record of δ 18O in the Malan ice core indicated that the warm-season air temperature variations displayed a general increase trend, the 20th-century warming was within the range of natural climate variability, and the warmest century was the 17th century while the warmest decade was the 1610s, over the entire study period. The “Medieval Warm Epoch” and “Little Ice Age” were also reflected by the ice core record. The dust ratio in the Malan ice core is a good proxy for dust event frequency. The 870-year record of the dust ratio showed that dust events occurred much frequently in the 19th century. Comparing the variations of δ 18O and the dust ratio, it is found that there was a strong negative correlation between them on the time scales of 101–102 years. By analyses of all the climatic records of ice cores and tree rings from the northern Tibetan Plateau, it was revealed that dust events were more frequent in the cold and dry periods than in the warm and wet periods.

Mid to late holocene climate evolution of the lake telmen basin, north central mongolia, based on palynological data

Palynological and sedimentological data from Lake Telmen, in north-central Mongolia, permit qualitative reconstruction of relative changes in moisture balance throughout the mid to late Holocene. The climate of the Atlantic period (7500–4500 yr ago) was relatively arid, indicating that Lake Telmen lay beyond the region of enhanced precipitation delivered by the expanded Asian monsoon. Maximum humidity is recorded between ∼4500 and 1600 cal yr B.P., during the Subboreal (4500–2500 yr ago) and early Subatlantic (2500 yr–present) periods. Additional humid intervals during the Medieval Warm Epoch (∼1000–1300 A.D. or 950–650 ago) and the Little Ice Age (1500– 1900 A.D. or 450–50 yr B.P.) demonstrate the lack of long-term correlation between temperature and moisture availability in this region. A brief aridification centered around 1410 cal yr B.P. encompasses a decade of cold temperatures and summer frost between A.D. 536 and 545 (1414–1405 yr B.P.) inferred from records of Mongolian tree-ring widths. These data suggest that steppe vegetation of the Lake Telmen region is sensitive to centennial- and decadal-scale climatic perturbations.

1738 years of Mongolian temperature variability inferred from a tree‐ring width chronology of Siberian pine

1738 years (AD 262–1999) of temperature variability are inferred from tree‐ring widths of Siberian pine at Solongotyn Davaa (Sol Dav), a timberline (2420 m) site in Mongolia. This chronology can account for 33% of the temperature variance from 1882–1993. The warmest conditions over the past millennium are during the 20th century. The 1999 ring width has the highest index value over the past millennium. Both warmer and colder intervals are inferred during the “Medieval Warm Epoch”. The most severe cold occurred in the 19th century. Unusual cold and frost in AD 536–545 coincide with extremes in other proxies and historical accounts, confirming a widespread, catastrophic event. Trends resemble those of other Eurasian paleoseries, and hemispheric‐scale reconstructions over the past millennium. More chronologies such as Sol Dav are essential to improve coverage in the uncertain earlier centuries of these reconstructions and their estimates of natural variability relative to recent anthropogenic change.

The last ca 2000 years palaeolimnology of Lake Candia (N. Italy): inorganic geochemistry, fossil pigments and temperature time-series analyses

The palaeoenvironmental history of Lake Candia, a small, shallow, eutrophic lake in Northern Italy, is described for the last ca 2000 years. Sediment samples from a sediment core collected in autumn 1995 were analysed for a range of palaeolimnological indicators, which included the principal algal and sulphur photosynthetic bacterial pigments, as well as magnetic susceptibility, organic matter, carbonates, organic carbon, total nitrogen, total sulphur and various forms of phosphorus. An accurate sediment chronology was determined using 210Pb, 137Cs and 14C. The results show that throughout a first, long phase of the history of this period (from ca AD 100 to 1830; zone 1) the sediments have an organic carbon content of ca 10% d.w. and low concentrations of algal pigments, suggesting a moderately productive environment. Sedimentary carotenoids unique to anaerobic photosynthetic bacteria indicate a seasonally hypolimnetic anoxia during the whole ca 2000 year period. Clear effects of climate changes on lake productivity were inferred from the carotenoid, ß-carotene, okenone and organic carbon estimates. Values were higher in the warm periods before AD ca 660 and during the so-called Little Optimum of the Medieval Warm Epoch (AD ca 1100-1300), and lower during cold moist periods, such as the main phase of the Little Ice Age (AD ca 1550-1700). After AD ca 1830 (zone 2), anthropogenic impacts resulted in a sharp increase in lake trophic state, leading first to a decoupling of the trophic state from natural (climate) variability, and then to "cultural" eutrophication. The onset of this latter process in the Turin area has been set around 1830, when a sharp increase of sedimentary sulphur concentration took place.

Multiplicity of the Discrete Delay Time of the Response of the Solar Total Irradiance Variation to the Long-Term Solar Magnetic Cycle Amplitude Modulation Deduced from the Greenland 10Be Data.

We found an observational evidence of the multiplicity of the discrete delay time on the order of 200 and 1000 years of the response of the solar total Irradiance variation to the solar magnetic cycle amplitude variation in the time profiles of the variations. We used the10Be data in the annual layers of the ice cores of the Greenland as a proxy of the solar magnetic field variation. We also used the land air temperature anomalies, reconstructed from tree-ring growth rates, as a proxy of the solar total Irradiance variation. The delay time of 1000 years means that the Medieval Warm Epoch of the Earth around the 13th and 14th centuries is a result of release of heat stored in the solar convection zone around the 3rd and 4th centuries when the solar magnetic activity was high.

Archaeological evidence for climatic change during the last 2000 years in southern Africa

Shifting distributions of Iron Age villages in central and southern Africa provide independent cultural evidence for climatic change over the last 2000 years. A warm and wet period characterized the main spread of the Early Iron Age. Another wet period from about AD 900 to 1290—the Medieval Warm Epoch—permitted the build-up of large populations at K2 and Mapungubwe. The abandonment of Mapungubwe and simultaneous rise of Great Zimbabwe coincided with the beginning of the dry Little Ice Age, while a warm pulse in the 15th and 16th centuries created the conditions for mixed farming on the highveld. Another warm and wet period at the end of the 18th century contributed to the spread of maize, increased populations and military stress of the difaqane.

A 1200 year record of accumulation from northern Greenland

We present the first detailed study of regional and secular changes in accumulation rate from northern Greenland. Four 100–150 m ice cores from this previously little investigated region have been dielectrically profiled and a good chronology for all four ice cores established by modelling the density profiles and identifying volcanic peaks in the records. This made it possible to calculate the accumulation rates of each core. The current accumulation rates show that there is a large region of low accumulation rate to the northeast of central Greenland with drops in accumulation rate of 25% 150 km, and 50% 300 km from Summit. Relatively large variations in accumulation rate over time are seen in all the cores. We have compared the resulting accumulation-rate record, which should be related to changes in local air temperature over northern Greenland, with Scandinavian tree-ring records and have interpreted the data as showing an early Medieval Warm Epoch, but no pronounced “Little Ice Age” and no unequivocal greenhouse warming effect as yet in northern Greenland.

A 1200 year record of accumulation from northern Greenland

We present the first detailed study of regional and secular changes in accumulation rate from northern Greenland. Four 100–150 m ice cores from this previously little investigated region have been dielectrically profiled and a good chronology for all four ice cores established by modelling the density profiles and identifying volcanic peaks in the records. This made it possible to calculate the accumulation rates of each core. The current accumulation rates show that there is a large region of low accumulation rate to the northeast of central Greenland with drops in accumulation rate of 25% 150 km, and 50% 300 km from Summit.Relatively large variations in accumulation rate over time are seen in all the cores. We have compared the resulting accumulation-rate record, which should be related to changes in local air temperature over northern Greenland, with Scandinavian tree-ring records and have interpreted the data as showing an early Medieval Warm Epoch, but no pronounced “Little Ice Age” and no unequivocal greenhouse warming effect as yet in northern Greenland.

Climatic fluctuation in the Czech Lands during the last millennium

On the basis of documentary evidence, proxy-data and instrumental observations, the climatic fluctuation during the last millennium in the Czech Lands is analysed. According to narrative sources, the warmest period falls between the 1260s–1380s, documents for Lamb's (1984) Medieval Warm Epoch in 1150–1300 are missing. The prevalence of extremely cold and also rainy periods, as an expression of the Little Ice Age, is most conspicuous in the 15th century, in the 1590s and, with three interruptions, between the 1730s–1850s. Since the latter half of the 19th century a rising temperature trend has manifested itself. A regional climatic scenario for the model of global warming is discussed in relation to the observed trends in the Czech Lands.

Tree-ring and glacial evidence for the medieval warm epoch and the little ice age in southern South America

A tree-ring reconstruction of summer temperatures from northern Patagonia shows distinct episodes of higher and lower temperature during the last 1000 yr. The first cold interval was from A.D. 900 to 1070, which was followed by a warm period A.D. 1080 to 1250 (approximately coincident with the Medieval Warm Epoch). Afterwards a long, cold-moist interval followed from A.D. 1270 to 1660, peaking around 1340 and 1640 (contemporaneously with early Little Ice Age events in the Northern Hemisphere). In central Chile, winter rainfall variations were reconstructed using tree rings back to the year A.D. 1220. From A.D. 1220 to 1280, and from A.D. 1450 to 1550, rainfall was above the long-term mean. Droughts apparently occurred between A.D. 1280 and 1450, from 1570 to 1650, and from 1770 to 1820. In northern Patagonia, radiocarbon dates and tree-ring dates record two major glacial advances in the A.D. 1270–1380 and 1520–1670 intervals. In southern Patagonia, the initiation of the Little Ice Age appears to have been around A.D. 1300, and the culmination of glacial advances between the late 17th to the early 19th centuries.

Dendroclimatological Reconstruction for the Last Sub-millennium in Central Japan

Annually resolved winter temperature and summer precipitation of Central Japan were reconstructed for the past 800 years, back to AD 1177 from an absolutely dated ring-width chronology of Chamaecyparis obtusa. This chronology was constructed from 300-year-old living trees and old logs of early modern and medieval origins that exist in hundreds in the Kiso Forest on the foothills of Mt. Ontake (3,063 m a.s.l.). In general agreement with the well established past climatic change in Europe, the reconstructed winter temperature showed three distinctively different phases, i.e. a cooling trend toward the mid 1200s possibly corresponding to the termination of the Medieval Warm Epoch, followed by a long cold spell corresponding to the Little Ice Age till the early 1800s, and then by a conspicuous warming trend continuing up to present.

A 2000-Year Tree Ring Record of Annual Temperatures in the Sierra Nevada Mountains

Tree ring data have been used to reconstruct the mean late-season (June through January) temperature at a timberline site in the Sierra Nevada, California, for each of the past 2000 years. Long-term trends in the temperature reconstruction are indicative of a 125-year periodicity that may be linked to solar activity as reflected in radiocarbon and auroral records. The results indicate that both the warm intervals during the Medieval Warm Epoch ( approximately A.D. 800 to 1200) and the cold intervals during the Little Ice Age ( approximately A.D. 1200 to 1900) are closely associated with the 125-year period. Significant changes in the phase of the 125-year temperature variation occur at the onset and termination of the most recent radiocarbon triplet and may indicate chaotic solar behavior.

The climate of the last 2000 years in southern Africa

Until recently, relatively little was known of the exact nature of climatic change in southern Africa over the past two millennia. New research based on oxygen isotope analyses of cave speleothems and mollusc remains in shell middens, together with foraminifera studies of inshore marine deposits, palynological and micromammalian research and earlier dendrochronological work, has allowed more reliable identification of the effects of the 'Little Ice Age' in the subcontinent. Cooling prevailed from 1300 to 1850 with a warm episode occurring between about 1500 and 1675. In addition, the generally warmer period from about 900 to 1300 may have been associated with the Medieval Warm Epoch. Earlier distinctive events appear to have been a variable period of cooling from 600 to 900, a warmer period from about AD 250 to 600 and a notable interval of cooling between AD 100 and 200. Much of the evidence for the 'Little Ice Age' in southern Africa suggests that in the summer rainfall region drier conditions prevailed during the period of cooling. At the same time the winter rainfall region became wetter. This supports a previous postulation that as the tropical easterlies of the general circulation of the atmosphere strengthen and become more perturbed over southern Africa over extended periods, so the climate becomes wetter over the summer rainfall area. As the circumpolar westerlies strengthen and expand northward, so the summer rainfall region becomes drier, while the coastal Mediterranean winter rainfall region becomes wetter.

Holocene palaeoclimatic trends from palaeoflood analysis

Global correlations of time periods characterised by large floods are noted from northern and southern hemisphere rivers. A late 19th century flood period is recognised from the Mississippi (and some of the southwestern Rivers of the USA), the River Dee (Scotland) and the Orange River (South Africa). The period of the Little Ice Age can be clearly recognised from the flood record of several rivers and some indicate a double pulse (AD 900–1200; AD 1300–1600) which straddles the Medieval Warm Epoch. Although data becomes less reliable and telescoped with time the global flood record appears to show further flood periods between 3000-1800 yr B.P., 4000–5000 yr B.P., possibly 7000–9000 yr B.P. and it is likely that the Younger Dryas was also a flood period. The flood periods appear to coincide with cold and wet palaeoclimates. This work recommends that this research be continued and that a palaeoflood research data base be set up.

Holocene palaeoclimatol trends from palaeoflood analysis

Global correlations of time periods characterised by large floods are noted from northern and southern hemisphere rivers. A late 19th century flood period is recognised from the Mississippi (and some of the southwestern Rivers of the USA), the River Dee (Scotland) and the Orange River (South Africa). The period of the Little Ice Age can be clearly recognised from the flood record of several rivers and some indicate a double pulse (AD 900–1200; AD 1300–1600) which straddles the Medieval Warm Epoch. Although data becomes less reliable and telescoped with time the global flood record appears to show further flood periods between 3000-1800 yr B.P., 4000–5000 yr B.P., possibly 7000–9000 yr B.P. and it is likely that the Younger Dryas was also a flood period. The flood periods appear to coincide with cold and wet palaeoclimates. This work recommends that this research be continued and that a palaeoflood research data base be set up.