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The Little Ice Age and medieval warming in South Africa
Abstract
The Little Ice Age in South Africa, from around AD 1300 to 1800, and medieval warming, from before 1000 to around 1300, are shown to be distinctive features of the regional climate of the last millennium. The proxy climate record has been constituted from oxygen and carbon isotope and colour density data obtained from a well-dated stalagmite derived from Cold Air Cave in the Makapansgat Valley. 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. It was variable throughout the millennium, but considerably more so during the warming of the eleventh to thirteenth centuries. Extreme events in the record show distinct teleconnections with similar events in other parts of the world, in both the northern and southern hemispheres. The lowest temperature events recorded during the Little Ice Age in South Africa are coeval with the Maunder and Sporer Minima in solar irradiance. The medieval warming is shown to have coincided with the cosmogenic 10Be and 14C isotopic maxima recorded in tree rings elsewhere in the world during the Medieval Maximum in solar radiation.
... Often compared to modern climate change, the Medieval climate anomaly is spatially complex in Africa and responsible for short-lived but strong climatic reorganizations across the continent (Nash et al., 2016;Lüning et al., 2017Lüning et al., , 2018, giving a glimpse of how the modern increase in temperature might affect the ecology of the miombo woodlands. Based on oxygen and carbon isotopes from a stalagmite in South Africa, Tyson et al. (2000) noted that the temperature may have increased by over 3 °C during the Medieval climate anomaly. In general, two sunspot maxima (translated into warmer global temperatures) occurred during the Medieval climate anomaly at ca. 920-1020 CE and ca. ...
... In addition, this zone also exhibited an increase in C 3 grass phytoliths, which indicates the occurrence of shade-tolerant grasses and cooler conditions, supporting the interpretation of woodland expansion. This phytolith zone was concomitant with the start of the early phase of the Little Ice Age, which was characterized by glacier advances in the Northern Hemisphere from ca. 1300 CE onward, and which was responsible for decreased temperature and increased precipitation in some regions of Africa (Tyson et al., 2000;Russell and Johnson, 2007). Fire activity was relatively high in this zone (CHAR mean = 33 cm -2 yr -1 ). ...
... For example, over the course of the "early" Little Ice Age, the Lake Tanganyika basin and the area east of Lake Victoria extending as far as the Indian Ocean coast presented relatively humid conditions (Verschuren et al., 2000;Njagi et al., 2021), favoring tree encroachment. Based on cave records from South Africa, Tyson et al. (2000) suggested that temperature was around 2 °C below present levels during the Little Ice Age. In addition, Verschuren et al. (2000) observed that Lake Naivasha (Kenya) had a positive water balance and freshwater conditions from ca. 1270 CE to 1550 CE, interrupted by a brief drought episode from ca. 1380 CE to 1420 CE. ...
Building resilience to climate change in the Afrotropics hinges on accurately predicting the style and tempo of ecosystem responses. Paleoecological records offer valuable insights into vegetation dynamics, yet high-resolution data sets remain scarce in Africa. Here, we present a new radiocarbon-dated sediment core from Lake Tanganyika, capturing terrestrial ecosystem responses to hydroclimate variability and fire activity during the Common Era. Phytolith and macrocharcoal records reveal oscillations between grasslands and woodlands in the Zambezian miombo region, transitioning from “stable” to “unstable” states depending on fire disturbance levels. The expansion of grasslands was facilitated by reduced precipitation, increased fire activity, and ecosystem interactions. Our data sets provide new constraints regarding the timing and landscape responses within the Lake Tanganyika watershed to global hydroclimate changes, including the relatively dry Medieval climate anomaly (ca. 1000−1250 CE) and the two phases of the Little Ice Age. Cold and wet conditions, which favored tree encroachment, prevailed during the “early” Little Ice Age (ca. 1250−1530 CE), whereas drier conditions coupled with increased fire activity during the “main” Little Ice Age (ca. 1530−1850 CE) promoted the expansion of open grasslands. Significant changes in grassland-woodland communities were driven and modulated by hydroclimate and rapid ecosystem feedbacks. Fire activity served as both a disruptive force, facilitating the opening of landscapes and restricting the encroachment of trees, and a steadying control that promoted a grassland “stable state” in the tropical savannas surrounding Lake Tanganyika. Understanding shifting vegetation patterns throughout the Common Era offers valuable insights for developing biodiversity conservation strategies, sustainable land-use practices, and the maintenance of ecosystem services provided by miombo woodlands for millions of rural poor in the Lake Tanganyika basin.
... The temperature of the last millennium in southern Africa was characterised by positive anomalies during MWP, after which a variable, unstable and mostly cold climate prevailed during 1300-1850, corresponding to the LIA [90,91]. The temperatures for southern Africa over the last millennium were about 3 • C higher during MWP or about −1 • C lower during LIA, compared to the present day [91]. ...
... The temperature of the last millennium in southern Africa was characterised by positive anomalies during MWP, after which a variable, unstable and mostly cold climate prevailed during 1300-1850, corresponding to the LIA [90,91]. The temperatures for southern Africa over the last millennium were about 3 • C higher during MWP or about −1 • C lower during LIA, compared to the present day [91]. The very cold periods reported by Tyson and Lindsey [90] around 1600 and 1700 CE are replicated in the Chapman archive as years with lower rainfall. ...
... The very cold periods reported by Tyson and Lindsey [90] around 1600 and 1700 CE are replicated in the Chapman archive as years with lower rainfall. Tyson et al. [91] established that LIA had two mainly dry periods in 1300-1500 and 1675-1800 CE, alternating with a warmer period in 1500-1675 CE. Although a long dry period is evinced by the isotopic excursions between 1288 and 1306 CE, the wettest conditions were registered in the time frame 1379-1446. ...
A high-resolution climate archive was reconstructed based on carbon isotope analysis and radiocarbon dating of the Chapman baobab in northeastern Botswana. The Chapman baobab, which exhibited an open ring-shaped structure composed of six stems, collapsed in January 2016 during an intense El Niño event. Two samples belonging to the oldest stems were investigated in order to obtain a proxy rainfall record, which provides insight into the precipitation regime over the last millennium, evincing centennial and decadal scale variability. The results indicate that the Medieval Warm Period was marked by relatively stable precipitation, whereas rainfall variability and drought frequency increased during the Little Ice Age. The investigated area has experienced both wetter and drier conditions in the past. The wettest conditions of the last millennium were registered before 1450 while the driest period occurred in 1835. For southern Africa, inter-annual rainfall variability is mainly associated with sea surface temperatures in the Agulhas Current core region, which determine the east–west displacement of tropical temperate troughs. Previous studies suggested that positive sea surface temperature anomalies in the Mozambique Channel led to an eastward movement of the troughs but the Chapman record demonstrates a westward displacement in the past, causing drought in northeastern South Africa and wetter conditions in the central part of southern Africa. The positive rainfall correlation with SST anomalies reversed after 1900, causing a gradual decrease in precipitation and confirming the current aridity trend for Botswana. The results contribute to a better understanding of the past climate of southern Africa for which paleoclimate reconstructions remain scarce.
... The OSL chronologies (Tables 2 and 3; Fig. 4) constrain the onset of erosion at each site to the late Holocene, which was a time of regional and global climate variability, as exemplified by the MCA (~AD 900-1300) and Little Ice Age (LIA,~AD 1300-1800) (Mann et al., 2009). These periods of rapid climatic change were major and distinctive features of southern Africa's palaeoclimate (Tyson and Lindesay, 1992;Tyson et al., 2000;Nicholson et al., 2013;Nash et al., 2016) and have also been implicated in soil erosion dynamics in parts of eastern Africa (e.g. Kiage and Liu, 2009). ...
... Numerous studies report a shift to generally cooler and drier conditions in the SRZ around the MCA-LIA transition (e.g. Tyson et al., 2000;Holmgren et al., 2003;Ekblom, 2008;Ekblom and Stabell, 2008;Gillson and Ekblom, 2009;Chase et al., 2009;Nicholson et al., 2013;Sundqvist et al., 2013;Zhao et al., 2016). In northern and eastern South Africa, the δ 13 C Pafuri baobab series indicates an overall drying trend from AD 1075 to 1805 (Woodborne et al., 2015), and the lowresolution Wonderkrater pollen sequence suggests cool and dry conditions from AD 1400 to 1800 (Scott, 1982;Thackeray, 1999;Truc et al., 2013). ...
Soil erosion across South Africa's drylands occurs widely in the form of gullies and badlands (locally termed dongas) that have developed in colluvium and in valley fills along incised rivers. This erosion has commonly been attributed to land mismanagement, particularly since European settlement, but natural factors such as soil properties, local base level fall and climate change have also been invoked. To disentangle human and natural factors, we use optically stimulated luminescence (OSL) dating, supported by documentary and archaeological evidence, to constrain the timing and causes of donga formation at three widely spaced sites across interior South Africa. At all three sites, the exposed stratigraphy indicates that hillslopes and floodplains underwent net sediment accumulation during most of the late Quaternary, and that present‐day deep erosion is of a magnitude unprecedented probably within at least the past 100 ka. OSL ages indicate that the onset of erosion at each site significantly pre‐dates European incursion and instead was broadly coincident with abrupt climatic changes that occurred during the Medieval Climatic Anomaly (MCA, ~ ad 900–1300) and Little Ice Age (LIA, ~ ad 1300–1800). Based on correlation with palaeoclimate proxy records, we propose that erosion was triggered by abrupt hydroclimatic oscillations during the MCA, and continued during the LIA in response to climate‐driven, large floods. At these sites, soil type and local base level falls exert secondary controls on the specific locations, processes, rates and depths of erosion. In other areas of South Africa, clear links between land mismanagement and soil erosion have been demonstrated, but for sites where detailed investigations have yet to be undertaken, these findings challenge an often default assumption that soil erosion is necessarily attributable to human factors. Our findings have significant implications for soil erosion control strategies and assessment of South African dryland landscape response to future climate changes.
... °C . Palaeoclimatic records suggest climatic fluctuations over the last 2000 years, particularly during the Medieval Warm Epoch (900 to 1300 AD) and the Little Ice Age (1300 to 1850 AD) (Avery, 1992;Benito et al., 2011;Cohen et al., 1992;Hopper et al., 2018;Meadows and Baxter, 2001;Stager et al., 2012;Stevenson et al., 1999;Tyson et al., 2000;Tyson and Lindesay, 1992;Weldeab et al., 2013). ...
The introduction of herding-a way of life which centers around keeping herds of mobile domesticated animals-significantly changed the economic, social, and cultural landscapes of Africa during the last 10,000 years. Unlike in other parts of the world, herding spread throughout the continent thousands of years before farming and did not replace foraging in many places, giving rise to complex mosaics of foragers and food producers across sub-Saharan Africa making it particularly difficult to isolate 'herders' in the archaeological record. This is especially relevant in southern Africa where even short term/single occupation sites can reflect mixed economic activities. Despite its late adoption, around 2100 years BP in South Africa, current evidence suggests that stock keeping moved quickly throughout the western portion of the country. As a result, when Europeans arrived at the Cape of Good Hope in the 17th century, they encountered local people keeping large herds of domestic animals. Unfortunately, these large herds so visible ethnohistorically are archaeologically rare with very few sites producing positively identified sheep. Thus, we know very little about the socioeconomic mechanisms and dietary choices made by herders over the past 2000 years in South Africa. iii To find novel ways of identifying herding in the archaeological record of Namaqualand, my PhD research was the first study to combine ethnohistoric and ethnographic accounts with traditional archaeological methods and ceramic-bound lipid analysis to examine the socioeconomic motivations for keeping domesticates in the Namaqualand coastal desert of South Africa. This
... Isotopes were later applied to a stalagmite series from the Makapansgat Valley to yield first insights into regional temperatures during important global climate events, namely the Little Ice Age and Medieval Climate Anomaly. 17,18 The field continues to thrive, and is currently serviced by laboratories at the University of Cape Town, iThemba, and the University of Pretoria. The establishment of an Accelerator Mass Spectrometer and associated cosmogenic nuclide capabilities at iThemba is an important addition to these facilities 19,20 , making dating more accessible and affordable for local scientists. ...
... Post glacial climatic cycles, described above, stabilise at this time ie the last 2000 years, although a hot dry period known as the Medieval Warm Anomaly (MWA) or Medieval Warm Epoch (c 1300-650 cal BP) does appear to impact local conditions (Tyson et al 2000;Jerardino et al 2021). Peter Mitchell draws attention to 'El Niño events [that] usefully remind us of the value of situating southern African history within a global environmental context' (Mitchell 2017:46). ...
This research investigates the density and distribution of quartz deposited over an area measuring 70,000 m2 at Kurukop in the Nama Karoo, South Africa. Relationships between quartz artefacts, engraved depictions, water features and rock abrasions in archaeological sites has been hypothesised. However, despite other comparable engraved sites in the region, Kurukop comprises an unusual number of quartz artefacts and intra-site associations. To investigate possible relationships between features I used a combination of techniques. These include, first, mapping the engravings, water features and rock rubbings during a ground survey and by means of drone imaging. Second, obtaining quartz samples from two squares (SA1, SA2), counting and weighing them. Last, intercalating these data with measurements provided by the aerial map and ground survey. A number of trends can be observed indicating that the remains of previous activities probably influenced subsequent decisions, thereby determining spatial organisation of the site and markings. Moreover, I applied a rhythm analysis to the ethnoarchaeological dimensions of the study to consider the production of space in terms of permanence, returns and abandonment (temporality). The conclusion I draw is that the presence and absence of water appears to have influenced the way in which hunter-gatherers, and later herders, chose to interact with and mark the site.
... The peak at 0.5 ka cal BP-also evident in the Stone Age dated human remains-seem to correspond with peaks in both records. Additionally, shorter, and higher resolution, paleoclimate records (not shown here) attest to regional effects of global climate events over this period, including the Medieval Warming Anomaly (∼1000 to 1300 CE) and the Little Ice Age (∼1500 to 1800 CE) (e.g., Tyson et al. 2000;Holmgren et al. 2001). ...
The study of human remains can provide valuable information about aspects of past populations. Here we present an updated database consisting of 590 radiocarbon ( ¹⁴ C) dates for human remains from Holocene South Africa before European contact. We calibrated or recalibrated all the previously published dates using the most recent calibration curve for the southern hemisphere. Each date is roughly georeferenced and plotted according to their Stone Age or Iron Age contexts, revealing the broad distribution pattern of dated Holocene human remains across South Africa—perhaps reflecting aspects of past population distribution and densities, but also underscoring historical collection practices, archaeological research focus, and preservation conditions. We use Kernel Density Estimation models to show peaks and troughs of dated remains through time, with Later Stone Age peaks at ∼5.5 ka cal BP, ∼2 ka cal BP and ∼0.5 ka cal BP, and Iron Age peaks ∼1.1 ka cal BP and ∼0.5 ka cal BP, some of which show broad correspondence to climatic data. Our data, based on dated remains only, do not provide a full reflection of past populations, and our large-scale, coarse-grained analysis cannot yet assess the reasons for the peaks in dated human remains in detail. Yet, the study provides a new resource, and a data-driven overview that highlights aspects to be explored with further contextual analyses against the available archaeological records, population histories and climatic indicators through time and across space.
... Paleoclimatic records for the regionbased on oxygen, nitrogen and carbon isotopesshow that the rainfall and temperature varied between AD 900 and the present (e.g., Smith et al. 2007Smith et al. , 2010Woodborne et al. 2015). These isotopic analyses indicate that, during the Little Ice Age (AD 1300-1800; Tyson et al. 2000), there was a ±1.4°C decrease in temperature accompanied by a decrease in rainfall (Woodborne et al. 2015). The SLCA also plays host to several different environment types including woodland in the form of a riparian forest, rocky hills, and grasslands (e.g., Eastwood & Blundell 1999;Plug 2000;Rutherford et al. 2010). ...
Rain-control in the Shashe-Limpopo Confluence Area (SLCA) is one sphere in which hunter-gatherer and farmer interaction is archaeologically visible. One avenue of examining this interaction is through faunal analysis. This paper presents an updated taxa list for one of the identified rain-control sites in the SLCA-Ratho Kroonkop. By identifying the taxa accumulated at Ratho Kroonkop and contextualising them using radiocarbon dates and relevant ethnographies, we were able to determine that particular animals were significant to the people who utilised the location as a rain-control site. Additionally, we were able to establish that this significance continued from the K2 period (AD 1000-1220) to the historic period.
The palaeoclimate archives of tropical and marginal-tropical Africa and their interpretation are presented and critically discussed. The importance of the geomorphological, sedimentological, and pedological archives, in addition to Quaternary glaciations, for climate reconstruction is particularly emphasized and related to Quaternary marine environmental reconstructions. Quaternary climate and landscape change can be better reconstructed in Africa than in Latin America because (i) the African continent extends over 8000 km on either side of the equator to ca. 35° to the north and south, (ii) more than three-quarters of its area lie within the tropics (23.5° N and S), (iii) major mountain systems neither meridional (like the Andes of South America) nor latitudinal cross the continent, and (iv) the change from hot and humid tropical equatorial rainforest to the extremely arid desert is exemplary. The climatic and vegetation zones are interrupted in their latitudinal formation only in the mountains of East Africa. Early and middle Quaternary palaeoclimate archives (e.g. lake formations, moraines, speleothems, dunes) provide evidence of thermal and hygric climate fluctuations since the early Quaternary, which were much greater than the climate changes of the last glacial cycle. Cold phases are characterized by greater aridity in the lowlands. Warm phases (interglacials) were more humid; since Marine Isotope Stage 11, 400,000 years ago, warm-stage humidity decreased. The orbital and solar influence on large and small climate variations is documented by many different palaeoclimate archives. Terrestrial African palaeoclimate records document Arctic influence north of the equator and Antarctic influence in southern Africa. Climate modeling rarely considers the terrestrial palaeoclimate data of the African tropics. The extent to which climate influenced human cultures is shown using the example of the Sahara and East Africa.
April-August temperatures are reconstructed from maximum latewood density and ring-width data for a tree-line site in the Canadian Rockies of Alberta close to Athabasca Glacier. The chronology primarily utilizes Picea engelmannii with some Abies lasiocarpa snags. This reconstruction (AD 1073-1983) is the longest densitometrically based summer temperature record from boreal North America. Mean temperatures from 1101- 1900 were 0.71°C below the 1961-1990 reference period and 0.33°C below the 1891-1990 mean of the instru mental record. The coldest interval was the first half of the nineteenth century and the major cold intervals, c. 1200-1350, 1690s and the nineteenth century, coincide with local and regional periods of glacier expansion. Warmer periods, c. 1350-1440 and in the present century, are also periods of higher tree-line or tree-line advance at the site. The 1961-1990 reference period is clearly warmer than any equivalent-length period over the last 800 years. This record of summer warmth reinforces evidence of significant warming at several high- altitude and high-latitude sites around the Northern Hemisphere in the late twentieth century. The reconstruction also indicates that glacier advances of the 'Little Ice Age' in the Rockies occurred during a period of fluctuating climatic conditions rather than a long period of sustained cold of several centuries duration.
Southern hemisphere and South African regional air temperature anomalies
for the period 1860-1996 are compared to borehole-derived surface
rock-temperature anomalies to assess the extent to which surface rock
temperatures reflect possible global warming in South Africa. The
warming of the southern hemisphere since the mid-nineteenth century is
evident in the regional air temperatures for South Africa. Following a
temperature increase to a maximum in the 1920s, the climate cooled until
strong warming recommenced in the mid 1970s. Highest temperatures have
been experienced in the 1990s. Borehole-derived surface rock
temperatures followed a similar pattern, but with a lag of a few decades
in the case of the 1920s maximum. The overall warming trend is clearly
evident in the rock temperatures. Despite uncertainties in the different
data sets, an encouraging degree of agreement exists between the
increase in rock temperatures during the twentieth century, the
corresponding regional South African air temperature increase and the
southern hemisphere counterpart.
High-resolution stable isotope variations and growth structure analyses of the last three millennia of a 6600-year stalagmite record at Cold Air Cave, Makapansgat Valley, South Africa, are presented. Growth layers, which are measurable over the last 250 years, are shown to be annual. The correlation between the width of growth layers and precipitation is strongly positive. Changes in&dgr;18O and&dgr;13C are positively correlated and inversely correlated to changes in the colour of the growth layers in the stalagmite. Variations in colour are directly correlated with mean annual temperature. Dark colouration is the product of increased temperature and mobilization of organic matter from the soil, and is associated with wetter summers and enhanced growth of C4 grasses. Darker colouring and enriched&dgr;18O and&dgr;13C reflect a warmer, wetter environment, whereas lighter colouring and depleted isotopic values are indicative of cooler, drier conditions. The dominant episode in the 3000-year record is the cool, dry 500-year manifestation of the‘Little Ice Age’, from ad 1300 to about 1800, with the lowest temperatures at around ad 1700. The four centuries from ad 900 to 1300, experiencing above-average warming and high variability, may be the regional expression of the medieval warming. Other cool, dry spells prevailed from around ad 800 to 900 and from about ad 440 to 520. The most prolonged warm, wet period occurred from ad 40 to 400. Some extreme events are shown to correspond well with similar events determined from the Greenland GISP2 ice-core record and elsewhere. Distinct periodicities occur within the record at around 120, 200–300, 500–600 and at about 800 years BP.
We have re-examined the dust record from the GISP2 ice core retrieved from central Greenland and found that the background dust concentration is modulated with a period of 11 years all the way back to ice from at least 100,000 yrs BP. The only known, relevant, naturally occurring phenomenon with such a period is the well-known solar cycle. We believe that the background modulation we observe is related to the solar cycle and discuss this hypothesis.
We measured stable oxygen isotope ratios and skeletal growth rates in the massive corals Pavona clavus and P. gigantea from the west coast of Isabela Island, Galapagos, to assess interannual to decadal climate variability in the eastern Pacific. Comparisons of instrumental data sets show that sea surface temperatures (SST) in the Galapagos region are representative of a broad portion of the eastern equatorial Pacific. The P. gigantea isotope record is nearly monthly in resolution, spans the period 1961-1982, and shows strong correlation with a Galapagos instrumental SST record. Cross-spectral analysis shows that SST can explain greater than 80% of the variance in δ18O at both the annual cycle and within the high-frequency portion of the ENSO band (3-5 years). The P. clavus record is annual in resolution, extends from 1587 to 1953 A.D., and was obtained from a 10-m diameter colony preserved within the Urvina Bay uplift. The isotopic record appears to be a very good, but not perfect, indicator of ENSO events. The dominant oscillatory modes, both within the ENSO and interdecadal frequency bands, shift to shorter periods from the early to middle 1700s and again from the middle to late 1800s. This may reflect major reorganizations within the tropical ocean-atmosphere system and suggests that tropical Pacific climate variability is linked across timescales ranging from years to decades. -from Authors
Models of southern African palaeoclimate implicate surface atmospheric circulation anoma lies as forcing large-scale changes during the Late Quaternary. The available proxy data are insufficient to test the models since they provide information about temperature and rainfall rather than surface circulation. A conceptual model is proposed which links coastal ocean temperatures with atmospheric circulation and allows a history of surface circulation to be inferred from sea-temperature data. A Holocene sea-surface temperature (SST) record was constructed by measuring the oxygen isotope composition of marine mollusc shells preserved in an archaeological cave deposit on the coast of the eastern Agulhas Bank, southern Africa. Radiocarbon-dating of individual shells allowed definition of the timing and timespan of events in the record. By serially sampling along the growth axis of each shell, information was obtained about intra-annual variability as well as millennial-scale trends. During the early Holocene, the sea surface on the eastern Agulhas Bank was colder than it is at present. Maximum summer and winter temperatures obtained 5800 years ago, exceeding by more than 2°C those recorded in the region today during non-El Nino years. On average, temperatures remained high for the following 1500 years but dropped again during the Late Holocene. At 650 BP, at the start of the 'Little Ice Age' in southern Africa, the surface waters on the eastern Agulhas Bank were colder during both winter and summer.
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.
The coincidence between the Maunder Minimum of solar magnetic activity from 1645 to 1715 and the coldest temperatures of the Little Ice Age raises the question of possible solar forcing of the Earth's climate. Using a correlation which we find between measured total solar irradiance (corrected for sunspot effects) and a Ca II surrogate for bright magnetic features, we estimate the Sun's radiative output in the absence of such features to be 1365.43 W/m2, or 0.15% below its mean value of 1367.54 W/m2 measured during the period 1980 to 1986 by the ACRIM experiment. Observations of extant solar-type stars suggest that the Ca II surrogate was darker during the Maunder Minimum. Allowing for this, we estimate the total solar irradiance to be 1364.28 W/m2 or 0.24% below its mean value for the 1980 to 1986 period. The decrease in the global equilibrium temperature of the Earth due to a decrease of 0.24% in total solar irradiance lies in the range from 0.2°C to 0.6°C, which can be compared with the approximately 1°C cooling experienced during the Little Ice Age, relative to the present.
The most prominent Holocene climatic event in Greenland ice-core proxies, with approximately half the amplitude of the Younger Dryas, occurred ˜8000 to 8400 yr ago. This Holocene event affected regions well beyond the North Atlantic basin, as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane. Widespread proxy records from the tropics to the north polar regions show a short-lived cool, dry, or windy event of similar age. The spatial pattern of terrestrial and marine changes is similar to that of the Younger Dryas event, suggesting a role for North Atlantic thermohaline circulation. Possible forcings identified thus far for this Holocene event are small, consistent with recent model results indicating high sensitivity and strong linkages in the climatic system.
The climatic history over South Africa during the past few centuries is modelled by mathematical inversion of perturbations in temperature profiles measured in boreholes drilled in solid rock. Preliminary investigation reveals that 19th and 20th century rapid warming of the ground surface commenced about 170 years ago and that on average surface temperatures have increased by 1.1K since then in comparison to the 0.8K rise observed in global air temperatures over land since the mid-18th century. Lowest temperatures derived from the South African borehole temperature data set were reached around 1790 in the last phase of the Little Ice Age when mean conditions were 0.3K cooler than in preceding centuries. The model is shown to have considerable potential for determining regional magnitudes and gradients of climatic change in the period before meteorological records. It may even be possible to resolve changes in climate earlier than the Little Ice Age in South Africa if temperature data from deep boreholes become available.