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Climate variability and societal dynamics in pre-colonial southern African history (AD 900-1840): A synthesis and critique.

ABSTRACT

The role of climate variability in pre-colonial southern African history is highly disputed. We here provide a synthesis and critique of climate--society discourses relating to two regionally--defining periods of state formation and disaggregation. The first period involves the eleventh-thirteenth century development of socio-political complexity and the rise of southern Africa's first state, Mapungubwe, followed by its collapse and the shift in regional power to Great Zimbabwe. The later period encompasses the early-nineteenth century difaqane/mfecane mass migrations, violence and ensuing state-building activity. To further our assessment, we consider the wider contentious issues of climate causation and determinism in a regional context, but dispute suggestions of paradigm shift towards simplistic environmental collapse. Nevertheless, we specifically point to ambiguities in palaeoclimate records, a narrative tendency toward monocausal explanations and a lack of integration among the literature as reasons for a sustained divergence in interpretation regarding the significance of climate. We move on to discuss the potential of integrative approaches to illuminate understanding of the complex interactions between past climate variability and human activity. In order to do so, we highlight interlinked concepts such as vulnerability and resilience as key for bridging the gap between the natural and social sciences. To conclude, we point to future climate-society priorities and ways forward in the form of research areas, data prospects and questions.

KEYWORDS

Climate variability, southern Africa, Mapungubwe, Great Zimbabwe, difaqane/mfecane.

INTRODUCTION

State formation and decline marked the second millennium AD in south-east and central southern Africa (Figure 1). Bantu-speaking agropastoralists came to the region in the early first millennium AD, (1) and the evolution of dispersed farming communities and parochial chiefdoms into complex states has provoked much scholarly interest. The initial emergence of socio-political complexity and large polities is rooted in the Shashe-Limpopo basin, where by the late-first millennium, trade links had been established with the Indian Ocean network at Chibuene. (2) Succeeding the Zhizo people at Schroda (c. 900-1000), the leaders of the Leopard's Kopje people (c. 1000-1220 at K2) developed a new socio-political order and are said to have established sacred leadership. This process materialised in the development of southern Africa's first territorial state, Mapungubwe (c. 1220-1290), and the emergence of the Zimbabwe Culture, an archaeological term incorporating several polities defined by factors such as class distinction and monumental architecture. (3)

Around the time of Mapungubwe's decline, regional power shifted north to the Zimbabwe plateau. One Zimbabwe Culture site, Great Zimbabwe, grew to become an urban complex home to around 18,000 people, capital of an estimated 60-90,000 [km.sup.2] state territory, and dominated regional power relations for 150 years. (6) Upon its decline (c. 1420-1450), two successor states emerged; the Mutapa and the Torwa. (7) The following centuries saw persistent warfare and the onset of colonial influence, first from the Portuguese on the Mozambique coast and later the Dutch and the British in the south-west. At the beginning of the nineteenth century the difaqane/mfecane, a period of widespread political change, warfare and demographic upheaval, transformed the ethnological and socio-political organisation of southern Africa and resulted in further state-building activity. (8) By AD 1890, however, region-wide colonial rule was established and ended the Bantu state formation and disaggregation cycles that spanned much of the second millennium AD.

The nature of these recurrent shifits in power has been extensively debated since historical and archaeological investigations began, yet the causal mechanisms of these processes remain contested. Within various disciplines and through diverse methodological approaches, an array of explanations has been put forward. These include links to the Indian Ocean trade network and control over trade goods, (9) wealth in cattle, (10) control over resources such as gold and ivory, (11) external economic changes affecting demand for these resources, (12) the ideology of sacred leadership, (13) warfare and coercion, (14) human-induced environmental degradation (15) and colonial influence. (16) In the last two decades, however, there has been an upsurge in the literature on the past relationships between climate variability and human activity regarding both southern Africa and further afield. Indeed, precipitation variability has been causally linked to the defining moments of the rise and decline of the Mapungubwe and Great Zimbabwe states, the origins of the difaqane/mfecane and the rise of the Zulu kingdom. (17) It is this often-controversial debate over the role of climate that forms the focus of this article.

The first part of this paper comprises a synthesis and critique of the extant hypotheses and dominant approaches regarding possible regional climate-society linkages. To further this appraisal, we pay particular attention to the contentious issues of climate causation and determinism and their critique in a wider global context. This is an important task, as recent suggestions of a paradigm shift towards environmental collapse raise pertinent questions over the premise of climate as a chief causal factor. Additionally, despite the growing body of global climate history literature, the regional climate-society hypotheses have seldom been opened up for discussion to a wider audience outside the region. The defining periods mentioned above nevertheless provide transforming issues of environmental change, state formation and disintegration, competition for resources, human security and, in the latter case, mass violence and migrations. Given its high environmental vulnerability, adaptability and capacity for change, therefore, southern Africa constitutes an interesting case for the application of interdisciplinary approaches regarding the complexity of these interactions that have moved to the fore in other regions. (18) We consequently attempt to further related research aims by discussing the potential of concepts such as vulnerability and resilience and, above all, the further integration of diverse data sources, to enhance understanding of the role of climate in southern African history.

CLIMATIC DISCOURSES AND THE EVENTS OF THE SECOND MILLENNIUM

The effect of climate on human activity and wellbeing is, in the broadest sense, first mediated through its impacts on the biophysical realm. In the southern African case, the quantity and timing of precipitation are particularly implicated due to their critical role in food production and general subsistence. (19) Consequently, it has been argued by many that changes in moisture availability on various temporal scales would have inevitably impacted on the societies and economies of the time. In the specific region under consideration here (Figure 1), precipitation is characterised by high spatial and temporal variability. The majority of its rain falls between November and March, and it thus constitutes the Summer Rainfall Zone (SRZ). (20) Abrupt changes in moisture are present in the SRZ over the long-term (multi-decadal and centennial scales), with persistent near-decadal dry and wet phases reported over the last six millennia. (21) According to various palaeoclimate proxy data, the last 2,000 years have witnessed substantial variability in rainfall and temperature regimes (Figure 2). (22) This long-term variability is believed to ft to a general model of atmospheric forcing, where between latitudes 10-22[degrees]S, latitudinal displacements of the Inter-Tropical Convergence Zone (ITCZ) and associated atmospheric forcing are the main agents modulating rainfall. (23) This hypothesis implies that in periods of anomalously warmer global temperatures, the ITCZ would be strengthened over southern Africa, resulting in more rainfall in the SRZ, whereas the inverse is the case in periods of cooler global temperatures. This mechanism is also believed to account for the marked long-term antiphase relationship between precipitation in the SRZ of southern Africa and the bimodal rainfall region of East tropical Africa. (24) Further linked to this is the position of the circumpolar westerlies, whereby an equator-ward shift in their northern margins increases precipitation in the Winter Rainfall Zone (WRZ) in south-west southern Africa, but is thought to restrict the southward mobility of the ITCZ, reducing SRZ rainfall. In the south-east, the adjacent tropical Indian Ocean is the primary source of moisture, meaning that sea-surface temperature variations in the south-western Indian Ocean are especially significant. For example, a warmer ocean would mean strengthened south-easterly trade winds, resulting in more moisture coming directly from the ocean. (25) High inter- and intra-annual precipitation variability strongly linked to coupled ocean-atmosphere phenomena such as the El Nino Southern Oscillation (ENSO) is also apparent. (26) However, complexities in developing palaeoclimate data from the southern hemisphere low latitudes mean that this inter-annual variability is seldom reflected in proxy records and, for much of the pre-instrumental period, relatively sparse and limited resolution data are relied upon. (27)

Publications over the last two decades have posited these palaeoclimatic shifits in moisture availability, as well as shorter-term wet or dry conditions detected in some proxy and man-made climate records, as stimulants for societal change. While we hereafter review these climate-related hypotheses, we also make brief reference to a wider range of factors, and their coalescence, which may have impacted upon societies. A full analysis of these wider factors falls beyond the scope of this paper, and they are discussed to great extent elsewhere. (30) Moreover, this paper will focus on certain states and periods (particularly those shaded in Figure 2) due to the suggested climate-society linkages in the literature. However, it would be misleading to think that nothing of significance happened outside their frontiers or time-span. Accordingly, we are further cognisant of the other peoples and states that populated precolonial southern Africa. (31)

The pre-colonial period in the last millennium is most often depicted as a transition from primitive to complex society, involving increased socioeconomic and political sophistication and a linear trajectory of states rising and falling. (32) The development of this complexity is set at the beginning of the second millennium, and the Zhizo-Leopard's Kopje-Mapungubwe cultural development sequence at the Shashe-Limpopo confluence is widely believed to have played a critical role. (33) Climate has here been linked with several processes that culminated in the rise of Mapungubwe, southern Africa's first urban centre and state capital. Primarily, this relates to the interpretation that the period AD 900-1300 was the manifestation of the regional equivalent of the 'Medieval Climate Anomaly' (MCA) in Europe, which resulted in overall warmer and wetter conditions. (34) Although precipitation in this period has since been shown to be more variable than initially realised (Figure 2), agricultural expansion permitted by generally wetter conditions enabling population growth is thought to have been key to Mapungubwe's rise. (35) Leopard's Kopje people moved north into the basin at around AD 1000, displacing the Zhizo people who mostly moved west to Toutswemogala in present-day Botswana. (36) The ranked, kin-based Leopard's Kopje society centred at K2 took over trade relations with the Indian Ocean network, and is also said to have taken advantage of the 'favourable' climate at the time, cultivating sorghum and millet on the foodplains of the Shashe River. (37) As well as evidence for contemporaneous wetter conditions from palaeoclimate data (Figure 2), this suggested climate favourability stems from the fact that, at present, large tracts of the Shashe-Limpopo basin are semi-arid and in most years receive insufficient rainfall to support even modest subsistence cultivation. On this basis, the archaeological evidence for agricultural activity expansion from the eleventh-thirteenth centuries has been used as a primary indicator for climate-permitted human activity. (38) According to Tom Huffman, flooding and its silt deposits would have been a seasonal occurrence in normal years, given the inferred climatic conditions at this time, potentially giving multiple yields of sorghum and millet in an extended growing season. (39) In this interpretation, climate was a major facilitator of population growth that contributed to the development of societal complexity. Others place less importance on agriculture and consequently climate, arguing that the pathway towards complexity and state formation was predominantly built upon cattle wealth and its transformation into power on the basis of the distribution of herds to loyal followers. (40) Nevertheless, in both cases surplus wealth from the Indian Ocean trade network is frequently linked as a tipping point, augmenting and intensifying pre-existing wealth and social differentiation from cattle ownership. (41)

At around AD 1220, the Leopard's Kopje capital shifted from K2 to Mapungubwe, and with it came development of the first class-based bureaucracy in southern Africa. (42) Explanations for this shift are few, though a prominent theory relates to the ideology of sacred leadership. (43) Here, rain also plays a pivotal role. Relatively recent archaeological and ethnographic research has provided multi-layered evidence, albeit sometimes contested, (44) regarding this ideology and the corresponding 'worldview' of the governed population. This cognitive model relies on the disputed view that individual behaviour was governed by rules and regularities, and therefore that clusters of symbols in the archaeological record give meaning to social organisation. (45) At Mapungubwe and later Zimbabwe Culture sites, sacred leadership is in this case said to be based on a mystical relationship between the leadership, ancestors and God, who made it rain. Although rainmaking (a ritual process conducted by professional rainmakers to bring rain) was conducted by Bantu-speaking people long before Mapungubwe rose to prominence, this model implies that the Mapungubwe leadership altered the existing rainmaking system to enhance and entrench their legitimacy. Importantly, in this interpretation, rain and agricultural success were placed in the hands of the leadership, meaning this new elite 'Zimbabwe Pattern' rainmaking system constituted a 'nationalised' version of the previous system. (46) It is on this basis that Huffman speculates about the impact of drier conditions reflected in certain palaeoclimate records in the early-thirteenth century (Figure 2) in relation to their coincidence with the shift to Mapungubwe and the origin of the new rainmaking system. This hypothesis proposes that the return of generally wetter conditions was interpreted as a supernatural sanction, facilitating the rise of the new order and accounting for the placement of palaces atop old rainmaking hills thereafter. In accounting for this transformation of society and early state formation in the Shashe-Limpopo basin, climate has been suggested to play a pivotal, if not ultimate, role as part of a suite of factors, including trade links, cattle wealth and sacred leadership. Indeed, coupled with its palaeoecological setting, rainfall is seen as the key variable and, without sufficient quantity, it is claimed that the same processes could not have operated in the basin today. (47)

It is perhaps not surprising, then, that a change in moisture availability has also been linked to the decline of the Mapungubwe state at around AD 1290. Archaeologists and climatologists have strongly linked this with the apparent contemporaneous onset of the 'Little Ice Age' (LIA), largely due to an earlier coincidence between certain palaeoclimate records (Figure 2) and the dating of archaeological sites. (48) In this explanation, abrupt LIA cooling and drying put an end to this time of plenty, adversely impacting the viability of foodplain agriculture on which a population of several thousand was dependent, leading to state collapse. (49) Accordingly, due to the prevailing worldview, agricultural failure was interpreted as supernatural displeasure in the king's rule, potentially leading to a succession dispute, the abandonment of the town and perhaps even the Shashe-Limpopo basin as a whole. (50) Pointing to the resilience of local socio-ecological systems to change, however, Munyaradzi Manyanga disputes the simplicity of this explanation. Manyanga provides evidence of occupation in the basin after AD 1300, suggesting that political decay was not matched at several commoner sites on the Zimbabwean side of the basin. This is put down to the resource exploitation potential of local circumscribed environments and ecological niches which offered diverse subsistence opportunities. (51) While arguments against the linearity of widespread environmental degradation and depopulation as an adequate causal explanation are convincingly made, this evidence does not fundamentally challenge the assertion of climate-driven agricultural system collapse leading to state decline. Furthermore, it is questionable to what extent a subsistence buffer of circumscribed environments could sustain the Mapungubwe state as an entity in the event of suggested sustained drier conditions. This brings the model of rainmaking and political security at the capital into focus once again, specifically the extent to which this relationship could have affected or destabilised the political, social and economic vulnerability, structure and security of the state as a whole. Others have also countered this linkage, suggesting that other palaeoclimate records point to a later onset of the LIA, therefore meaning the viability of subsistence cultivation was not under threat as the climate was still relatively wet. (52) In addition to these predominantly climate-driven explanations, changes in the dynamics of the Indian Ocean trade and the contemporary increased international demand for gold have been linked to Mapungubwe's decline. In this view, Great Zimbabwe and its leadership were ideally placed to take control of the gold trade at a time of high international demand and therefore could have outcompeted a troubled Mapungubwe. (53) It is further important to note that in this period Nguni and Sotho-Tswana migrations to southern Africa occurred at around AD 1100 and 1300 respectively, probably from a nucleus in the interlacustrine region of Africa (Figure 1). (54) These too have been causally, although highly speculatively, linked with climatic fuctuations on the basis of the antiphase relationship in precipitation variability between southern and East Africa. This theory implies that inverse precipitation patterns between the two regions in palaeoclimate records around these times were a dominant push factor driving these groups to less populated areas in southern Africa. (55)

Upon Mapungubwe's decline, it is now generally agreed that a cultural diffusion as opposed to a simple northward movement of Mapungubwe people onto the Zimbabwe plateau took place. (56) A widely suggested implication, however, is that the Zimbabwe plateau offered a more favourable environment and climate for the support of a large urban complex and territorial state. (57) Indeed, the spatial variability of the regional climate is one of several proposed factors relating to the enhanced economic base of Great Zimbabwe as both an urban centre and a large state. specifically, climatic conditions in the 'high' rainfall zone along Zimbabwe's south-east escarpment are suggested to have allowed a fourishing agriculture in the hinterland of Great Zimbabwe. (58) In attempting to clarify this link between favourable environments and state formation, Innocent Pikirayi focuses on the issue of resource control. (59) Accompanying control over trade, this hypothesis points to the centralised authority of Great Zimbabwe and its elite as a product of the need to manage the variety of environmental assets and hazards, and perhaps crucially the gold deposits in the hinterland of the state. (60) Huffman adds that a Mapungubwe dynasty probably introduced class structures at Great Zimbabwe, involving the incorporation of a similar ideology and related practices such as the supernatural link to the sacred leadership and rainmaking. (61) This structuralism is disputed, however, on the basis that interpretation of socio-political dynamics at Great Zimbabwe based on findings from the Shashe-Limpopo is fawed and unsupported by the material culture at the site. (62) Moreover, Pikirayi and Chirikure add that it would have been suicidal for a chief or leader to entrust rainmaking functions to himself as it would have invited political instability or anarchy. (63) This may be even more pertinent a point if climate variability and rainmaking was indeed a significant pathway to a loss of authority at Mapungubwe.

Climate has received comparatively less attention as a factor in the decline of the state. Yet some speculation emerged suggesting that the cool-dry conditions observed in selected palaeoclimate records in the fifteenth century (Figure 2) undermined the agricultural base of Great Zimbabwe and its increasing population. (64) This was later dismissed because of Great Zimbabwe's location in a 'high' rainfall zone, meaning agriculture here was viable even with a drier climate most of the time. (65) Conversely, due to the conflicting signals and interpretations of palaeoclimate data at this time, others assert that the abandonment of the state occurred at a time of generally warmer and wetter conditions, meaning climate was not a central factor. Pikirayi endeavours to consider the dynamism of the period and is critical of the way this is often negated in studies. (66) In his view, a key point relates to the expansion of the state territory throughout the fourteenth century, possibly to obtain further arable land and gold resources for the Indian Ocean trade. This line of thought proposes that the height of state expansion set the conditions for its decline by a process of overstretch and thus, with the spatial shifits in demographic and economic power, came breakaway units, the gradual loss of control over the gold trade and the rise of successor states such as the Torwa and Mutapa. (67)

The mid-fifteenth century saw the emergence of the two successor states: the Mutapa in the north and the Torwa at Khami. The following period was marked by recurrent warfare on the Zimbabwe plateau and emigration and defensive aggregation in the south-east. (68) This is thought to have reflected the changing dynamics of regional power and trade, in part due to the new influence of Portuguese mercantilism, which usurped the Muslim traders on the Mozambique coast from the sixteenth century onwards. (69) Portuguese sources state that Khami was abandoned in the early-seventeenth century after it was destroyed by fire, while the Torwa state as a whole fragmented during the 1640s due to civil war. (70) In the north, the Mutapa dynasty apparently consolidated power by capitalising on the decentralised nature of groups on the northern Zimbabwe plateau and was governed from shifting centres of power in accordance with changes in dynasty and resource availability. (71) Making use of Portuguese documents, Pikirayi broadly considers the role of environmental change in this period. (72) While references to weather and climate are too sporadic to be useful for any formalised documentary climate reconstruction, the climatic information that does exist states that the last three decades of the sixteenth century and the year AD 1714 were severely dry in the lower Zambezi. In the former case this apparently disrupted food availability and led to cannibalism and in the latter, when coupled with a smallpox epidemic and civil wars, drought contributed to extensive mortality. (73) What is most evident from the written sources relating to Great Zimbabwe's successor states, however, is that political succession and security were volatile and often subject to forceful intervention. This only reinforces the difficulties of understanding potential causal factors and their interaction in the centuries before the written record.

The Rozvi at Danangombe later reunited the Torwa area, and were also involved in warfare with the Portuguese in the late-seventeenth century, though they eventually succumbed after several encounters with early-nineteenth century difaqane/mfecane groups. (74) The difaqane/mfecane was a period of widespread insecurity in the early-nineteenth century that directly or indirectly affected the whole region and involved increased raiding, migration and warfare, leading to revolutionary socio-political change and state formation. (75) The causes of this period are highly contentious and, although possible climatic pathways have received less focused attention recently, these are a recurrent theme, particularly in the mfecane origin area between Delagoa Bay and the Thukela River (Figure 1). Earlier work focused on a potential late-eighteenth century imbalance between population pressure and resources. (76) Jeff Guy, for instance, argued that the need for access to a range of seasonal vegetation and pasture types governed the location of settlement and that, as a result of land degradation coupled with early-nineteenth century drier conditions, several centralised polities emerged in response to the competition for diminishing resources. (77) However, Guy only considered pastoral production, and scant evidence supported the claim of human-induced land degradation leading to a resource breakdown. Martin Hall advanced thoughts on potential climatic pathways using archaeological and dendrochronological data. (78) Implicit in this hypothesis is the introduction of maize to KwaZulu-Natal through Delagoa Bay sometime around the early- to mid-eighteenth century. (79) Its cultivation, evidenced in the archaeological record by maize grindstones, is suggested to have had twofold implications. The first, as a result of the high yields of maize, is said to have increased the regional capacity for population growth. In this view, the extensive cultivation of maize was made possible by a period of increased rainfall towards the end of the LIA between 1750 and 1800. (80) The second implication of maize cultivation, however, was that its consumers were subject to increased vulnerability due to the crop's high sensitivity to water deprivation. (81) The heightened vulnerability of a large population is therefore said to have set the scene for drought-induced subsistence crises and famine in the generally dry decades of the early-nineteenth century. Using written records from early travellers and oral testimonies, Charles Ballard pointed to two major droughts as triggers. (82) For the first phase of the mfecane, a drought somewhere between 1800 and 1806-7 was key and a later drought between 1820 and 1823 was said to be particularly relevant for events on the Highveld. According to Ballard, the resultant famine during the first phase of the mfecane led to a serious breakdown of social, political and economic institutions among the northern Nguni, resulting in 'treks of survival' in search of food through barter in cattle or raiding and violence. The drive for a centralised state on the part of King Shaka and his predecessor, Dingiswayo, was therefore said to be undertaken with the chief objective of extending rule over a wider ecological zone for a larger range of grazing and arable lands. (83)

In a comprehensive regional study of the causal factors of the difaqane/mfecane, Elizabeth Eldredge importantly observed that climate can be part of the causal dynamics rather than a lone, monocausal driving-force mechanism. (84) The demographic upheavals and state formation processes were in her view rooted in increasing inequalities and cumulative environmental crises which impacted on long-standing competition over natural resources, fertile land and trade. Eldredge further examined factors such as the ivory trade at Delagoa Bay and its role in contributing to political amalgamation and increased inequalities on the basis of wealth accumulation. (85) According to this argument, the events of the early-nineteenth century are best understood by considering the occurrence of drought at a time when political events undermined traditional strategies of averting famine. specifically, increasing socio-economic inequality within and between chiefdoms fostered an unequal distribution of food in times of scarcity, resulting in the poorer elements of society becoming more vulnerable to famine. Subsequent severe drought then contributed to revolution and reorganisation among the northern Nguni groups at the very beginning of the nineteenth century. Huffman adds that cattle raiding increased from around 1780 to supply European ships, while falling elephant populations also encouraged the crisis, leading to stiff competition for declining export goods. (86) The later drought mentioned by Ballard around 1820-1823, or to 1826 according to Eldredge, is also noted to coincide with the extensive migrations in the interior, where similar processes may have occurred, resulting in an 'uninhabitable landscape'. (87) In these arguments, then, the search for food and wealth contributes towards an explanation for the migration of entire polities at this time. Still, although consideration of the mediating context on which climate variability and weather events act is a step-up from the sole consideration of environmental factors, it is questionable whether these conclusions can be as clear-cut when based predominantly on oral and documentary evidence. Other difaqane/mfecane hypotheses have included numerous Zulu- and Shaka-centric explanations regarding military organisation and aggression, the aforementioned trade hypothesis and colonial expansion, as well as a contentious view that critiqued the mfecane concept as a whole, claiming that it was a colonial myth to conceal white wrongdoing. (88)

As shown in this synthesis, climate and the environment have been put forward, often as coupled catalysts, in processes of state formation and disaggregation across the region. In some cases this has been contextualised against other hypotheses and events and in others it has been isolated as a monocausal mechanism in societal change. Bearing a major responsibility for these linkages is a seeming correlation between abrupt shifits in moisture availability or extended periods of precipitation variability inferred from palaeoclimate proxy data and evidence for societal change in the archaeological or written record. Considering this apparent coincidence, it is tempting to prescribe climatic variability as a chief and recurrent cause of cultural change, especially when referring to some earlier palaeoclimate records. (89) Nevertheless, climate variability as a causal factor of cultural and social change has been received controversially both in the region and in the global literature. It is therefore important to further question the approaches and methods that have led to the disputed view of climate as a driver in social and cultural change.

PALAEOCLIMATIC SHIfits AND THE CULTURAL SEQUENCE

As observed in other regions, the idea of a causal role for climate variability in shaping pre-colonial societal dynamics partly rose to prominence due to the development of higher-resolution palaeoclimate data. (90) A problematic situation arising from this, however, is that the conflicting signals and disputed interpretations of precipitation variability have directly contributed to divergent claims regarding causation. This is most evident in the case of the onset of the LIA and the decline of Mapungubwe. First, the signals of the T7 stalagmite oxygen isotope ([delta]18O) speleothem record from Makapansgat Valley (Figure 2, record 1) in particular gave rise to the thought that 'the coincidence of the Mapungubwe collapse with the end of the moist medieval warm period... strongly suggests that deteriorating climate was an important contributory factor in the decline of Mapungubwe'. (91) Later, however, palaeoclimate records from a combined T7/T8 stalagmite [delta]18O chronology from the same cave and faunal remains in the Limpopo Valley (Figure 2, records 2 and 5) led to markedly different interpretations regarding the onset of LIA cool-dry conditions, which were then thought to be around AD 1500-1600. This finding therefore provoked dismissals of the importance of climatic factors relating to Mapungubwe's demise. (92) Huffman disputes this interpretation, pointing to the trend towards drier conditions around AD 1300 in the T7/T8 [delta]18O record and the abandonment of settlements near the Shashe-Limpopo confluence as evidence. (93) His argument also states that, under the inferred cool-dry twelfth century conditions of the T7/T8 timeseries, populations could not have increased, while adding that a more widely reflected drier spell at the beginning of the thirteenth century, potentially important in the shift from K2 to Mapungubwe, is not reflected in the combined stalagmite record. Somewhat consistent, however is the signal for an LIA end-date between AD 1750-1800 (Figure 2). Yet evidence for early-nineteenth century climate change and societal upheavals was predominantly based on selective use of scattered oral testimonies, travellers' journals and one tree-ring record, giving a relatively over-generalised spatial and temporal insight into the climate dynamics of this critical period. (94)

Recent research in the fields of palaeoclimatology and historical climatology has further advanced this picture. The application of up-to-date age models and consideration of the variability between records has shown that it is less clear whether the MCA and LIA can be simply characterised as consistently warm-wet and cool-dry. (95) This is a crucial point, as climate--society debates have been in the grip of disputes over the timing of these periods. Equally important is that further analysis of the Makapansgat Valley speleothem records has indicated that regional surface temperature may be a more important driver of stalagmite [delta]18O than precipitation. (96) Given that a substantial proportion of the debate surrounding past climate--society interactions has involved discussion of these factors, these new findings warrant some re-evaluation. On this point, it has also been proposed that the use of stalagmite grey-scale data is a more suitable proxy for precipitation than of [delta]18O. (97) If this series is used, then an abrupt drought around AD 1270-1280 following half a century of higher rainfall is evident in the Makapansgat Valley combined record.

The volatility and divergence of these regional hypotheses illustrates the difficulties of interpreting past events when based on various interpretations of diverse palaeoclimate data sources. As evidenced in the synthesis above, research over the last few years has attempted to elucidate these initially speculative nature-culture linkages, nonetheless, a seeming temporal coincidence between datasets provides a basis for bold claims. Although the simplicity of these explanations may be attractive, general conclusions built on correlation can be misleading and cannot alone be relied upon to demonstrate the interactive relationship that exists between climate and society. Approaches that draw heavily on coincidence have commonly portrayed climate as a mono-causal driver of social and cultural change--yet causal links are both complex and non-linear. (98) This has led to misleading conclusions which portray humans as passive recipients of climate change, while underplaying the myriad of contemporary events taking place. Clearly, the state of the climate itself is crucial in any study of climate-society interaction, but is far from the only important factor. Simple cause-effect models are therefore inadequate and must consider the socio-economic, political and cultural context for a specific spatial area. (99) Care must be taken, then, to avoid reproducing the view of climate as a master narrative in human history, resonant of Baron de Montesquieu's eighteenth century declaration that 'the empire of climate is the first, the most powerful of all empires'. (100)

A REGIONAL 'ENVIRONMENTAL COLLAPSE' PARADIGM?

Some critics have recently argued that a global shift has taken place in contemporary archaeoanthropology and palaeoclimatology towards a burgeoning 'environmental collapse' paradigm, which gives primacy to environmental and climatic influence, while obscuring the social processes at the centre of human communities. (101) According to Guy Middleton, three broad environmental collapse mechanisms, each based on monocausal pathways, are symptomatic of this paradigm shift. (102) One sees climate as the primary driver of historical change; another views complex societies inducing ecological degradation and exceeding environmental carrying capacity; and the third concerns catastrophic environmental hazards such as earthquakes. Numerous other papers have also pointed to a recent global resurgence in climate and environmental determinism. In a seminal paper, Mike Hulme notes that the quantitative nature of climate data has frequently led to an elevated position for climate as an explanatory variable in human activity. (103) Applying this line of reasoning to the southern African past, Hulme's thesis is manifest in that quantitative and credible knowledge of past climate variability has frequently led to a direct transfer of authority regarding its potential consequences, in some cases allowing little for human agency, adaptation and innovation. A clear example regards the suggested climate-driven migrations of the Nguni and Sotho-Tswana from East Africa to southern Africa due to an inverse correlation in wet and dry conditions between the two regions. (104) Although some other lines of evidence are considered here too, the versatility of climate as a metanarrative explanation for cultural change is certainly evident, and assertions of climate-driven migrations should be treated with caution. Similarly, in an examination of the impacts of precipitation variability on vegetation in the Shashe-Limpopo basin using the SAVANNA model, it was concluded that 'Mapungubwe disappeared as a result of a decrease in mean annual rainfall'. (105) This is clearly a valuable exercise concerning rainfall-vegetation dynamics, but such claims are highly misleading. This explanation considers ecological factors only, meaning the results are taken out of context with only passing acknowledgement made to the complex interaction of other factors.

While climate has sometimes been depicted as a grand narrative, albeit perhaps unintentionally, it is equally the case that others have dismissed the role of climate as background noise, relegating environmental interaction to a footnote in human history. (106) Although it is indisputable that cultural choices were pivotal, this does not mean that climate or the environment should be discounted. Indeed, when critiquing past climate-society hypotheses, there is a risk of disconnecting from the basic facts that the climate of southern Africa is temporally and spatially highly variable and that recurrent drought is a factor that has been shown to influence the decision-making of pre-colonial states. (107) According to Hulme, these contrasting positions comprise the opposing fallacies of climate determinism and indeterminism, where the former has commonly been adopted by geographers, palaeoclimatologists and archaeologists, and the latter by historians. (108) Still, rather than a widespread revival of climate determinist explanations, the scepticism surrounding climatic causes may be in part due to the language employed and its narrative power. There is inherent difficulty in understanding causality in the distant past, and the complexity in communicating findings of relevance to numerous fields and sub-fields can result in suspicion. In many cases, particularly in those studies which examine a select part of a dynamic issue, it may be preferable to more explicitly acknowledge uncertainty or doubt when the evidence is insufficient. Climate-collapse linkages make for compelling narratives, but the reality is often a more nuanced picture. Major events are not always linked to major causes; rather, a suite of economic, social, political and environmental factors require consideration. (109)

On Middleton's second point, the hypothesis of environmental degradation has also received some regional attention. For instance, the exploitative nature of sustaining an increased population has been linked with environmental catastrophe at Great Zimbabwe. Graham Connah suggests that local population pressures could have had marked impacts on soils, vegetation and wildlife, even claiming that 'without fundamental changes in technology and agricultural system, it [Great Zimbabwe] was fated to destroy itself'. (110) Pikirayi takes a slightly more cautious stance and, although agreeing with the possibility of extensive ecological degradation, he urges that this was a consequence of mismanagement by the ruling elite. (111) However, scant evidence supports such assumptions and any standalone 'environmental collapse' conclusion, regardless of the level of socio-political culpability, would seem more categorical than the available evidence allows. Thus, although some of the environment-society linkages in southern Africa prehistory fall into Middleton's 'environmental collapse' categories, the view of climate variability as one of a broad range of actants is firmly present in the literature. It is therefore highly questionable whether the southern African debate regarding past climate-society interaction has undergone a paradigm shift towards environmental collapse. Nevertheless, future research would be strengthened by continuing to illuminate the interactive relationship that exists between climate and society as linked socio-ecological systems. This requires the further integration of disciplinary approaches, methods and sources.

INTEGRATIVE APPROACHES TO CLIMATE AND HISTORY

The challenge of providing integrated perspectives on climate and history is underscored by the fact that no discipline, methodological approach or data source is alone capable of formulating detailed linkages between human and natural systems. (112) Rather, an interdisciplinary approach is necessary to help clarify the complexities of past climate-society relationships. As relatively interlinked concepts, the frameworks of climate history, vulnerability, resilience, historical ecology and integrated history, to name but a few, have gained momentum in their ability to link palaeoclimatic, palaeoecological, historical and archaeological sources. (113) Our synthesis, considering the aforementioned frameworks, highlights three broad areas that can contribute to the study of climate-society interactions on various spatial and temporal scales in the southern African past:

(1.) Reconstructing and assessing past weather and climate variability

(2.) Investigating the vulnerability and resilience of past economies and societies to climate variability and extremes

(3.) Assessing the impacts of climate variability and their interaction with other factors

On the first point, it is important to consider the nature of the climate variability or weather event in question, according to criteria such as severity, frequency and spatial range, as well as its impacts on the biosphere.(114) Prior to the nineteenth century, this relates almost entirely to proxy sources. Clearly, the production of new-high resolution proxy records and the development of better temporally resolved records from existing sites would deepen understanding in this area. However, it is mostly the interpretation of one or two sources with sometimes ambiguous signals that has been the subject of extended debate in the region. In this case, the incorporation of a range of proxy-documentary data into analyses is key, with particular reference to the criteria listed above. This exercise should move away from blanket consideration of periods such as the MCA or LIA as wet or dry, as it has been shown that there is no evidence for multi-centennial periods over the last millennium being consistently warm-wet or cool-dry. (115) To establish a clearer picture of past precipitation variability, an updated statistical review of regional proxy data over this period is also needed. A similar undertaking has recently been carried out for the last 200 years through a regional multi-proxy precipitation reconstruction from both natural and man-made climate archives. (116) This study offers an inter-annual picture of precipitation variability for the SRZ and, along with databases such as the Africa-wide precipitation data set from 1801-1900, provides a dramatically enhanced picture of the timing and severity of weather and climate variability in this contested period. (117) Other sources can also add to these. One example is the wind observations in ships' logbooks from the Climatological Database of the World's Oceans (CLIWOC) and the English East India Company digitised dataset, which extend back to the mid-eighteenth century. As related above, the wind field in the south-west Indian Ocean is a key modulating factor in SRZ precipitation, whereby strengthened easterly flow generally implies greater precipitation. It is significant that these data surround southern Africa, due to ships' routes to the Far East (Figure 3), and so provide a means of reconstructing precipitation in a time period contemporaneous with the difaqane/mfecane and associated events. (118) Furthermore, data from the archaeology of rainmaking and ritual burning, as well as proxy ENSO records, offer other potential sources. (119)

As previously stated, however, it is not enough to base impact-analysis on climatic factors alone. According to Christian Pfster, the question as to 'which sequences of climatic situations mattered depends upon the impacted unit and the environmental, cultural and historical context'. (121) Translating this into data availability, inter-annual records are clearly desirable--yet few are available before the nineteenth century. Although this means that a substantially lower-resolution picture of human-climate interaction is achievable, it is possible to examine the mediating context in which climate interacted by illuminating concepts such as the vulnerability and resilience of societies and economies to climate and weather events. The concepts of vulnerability, often defined as the potential for loss, and resilience, the ability of a system to adjust its configuration under disturbance, are critical to assessing long-term risk and the magnitude of present weather and climate impacts, though they are often overlooked when considering the past. (122) These concepts relate to both the physical characteristics of local and regional environments and specific socio-economic and cultural relationships with the landscape. Taking the former point, this is evident in the example that the impacts of anomalously wet or dry conditions are not the same for all crops, nor for the same crop in different soils. It is therefore necessary to assess spatial differences in the environmental setting of past societies as a whole. One such example in a pre-colonial African context is found in the analysis of varying soil character, agricultural systems and local conservation practices in the society of Engaruka in East-central Africa, where several data sources are brought together to offer insight into the factors that contributed towards sustainability and vulnerability. (123) Moreover, following on from earlier work, a geoarchaeological approach has recently been employed to analyse the various soils that supported pre-colonial settlements in Zimbabwe, with particular reference to 'soil preferences'. (124) Further consideration of these factors in the region using state-of-the-art tools and datasets is still needed. Examination of past environments has been too often influenced by more recent perceptions, evidenced in the referral to agro-ecological zones designed to assess commercial farming potential in Zimbabwe. (125) This rigid zoning is misleading when considering small-scale peasant farming and provides a highly simplified picture of the range of exploitation and subsistence options available to pre-colonial societies. Resources such as the Soil Atlas of Africa provide more appropriate means to assess the environment-resource contexts of pre-colonial societies. (126) Soils are of course not the only important environmental factor to consider. For instance, research on rainfall-vegetation dynamics in the Shashe-Limpopo basin has identified the stability and resilience of grassland vegetation during past climate transitions. (127) A more extensive incorporation of such research dealing with the characteristics of the local and regional physical environment is therefore important before considering possible climate impacts.

It is also necessary to document the specific socio-economic and cultural relationships with the landscape, providing insight into socio-environmental vulnerability and resilience that goes beyond consideration of 'favourable' environments. On the contrary, it has been asserted that little can be said about why certain cultures should be susceptible to environmentally-triggered transitions. (128) We dispute this statement because of the simple fact that the effects of climate vary across the landscape due to economic, political, social and cultural differences. If this were not the case, the impact of adverse climatic conditions would be largely uniform across contemporary societies. Of particular importance here are links between the environment and the economic base of the society in question, particularly the range of subsistence and livelihood options available. A promising approach built on these factors is demonstrated by Anneli Ekblom in considering historical vulnerability and resilience in Chibuene, Mozambique. (129) Here, written, palaeoecological and archaeological evidence for changing livelihoods, resource utilisation and economic security is examined in order to illustrate socio-environmental vulnerability and resilience over multi-centennial periods. Manyanga has applied a similar approach to the Shashe-Limpopo basin, where, by focusing on resource exploitation in the range of micro-environments in the Mapungubwe state hinterland, new perspectives are offered regarding the subsistence options and economic base of the state beyond foodplain cultivation. (130) Such an approach could be fruitfully applied to states and people groups such as Great Zimbabwe, Mutapa and the northern Nguni, where, in the latter two cases, often underused written and oral sources supplement archaeological and environmental data. (131)

Furthermore, it is important to consider the potential role of adaptation and local knowledge systems such as food storage and distribution, which could have buffered or displaced external impacts in order to avert food scarcity, famine or social distress. Examining how society adapted to externally imposed change may be most insightful where the frontiers of archaeology and history overlap. With cautious treatment, re-examination of documentary sources and oral evidence may yield further clues regarding the internal workings of society which affect resilience, notably human resourcefulness, the rigidity of social and political networks and adaptation strategies. (132) Further elucidation in this area may also help to understand potential preparedness and response to environmental risk for Great Zimbabwe itself. However, these factors changed over time through both external and internal reasons, such as colonial influence, warfare and changing political dynamics, and these shifting parameters, though diffcult to assess, must be taken into account where possible. Although here we have only pointed to some areas, consideration of socio-environmental vulnerability and resilience may provide a more rewarding approach than a focus on abrupt events of change or 'collapse'. Indeed, this follows the observations of James McCann, who suggested that in Africa the 'real value of linking the environment to historical process may lie in a more subtle, nuanced view of how environmental conditions set a context for social and historical interaction'. (133)

To make any sort of statements on the impact of past climate variability, and in the absence of long, continuous and homogenous data records, comprehensive analytical models such as that in Figure 4 (b) are helpful. (134) This by no means advocates a rigid, universally applicable model for a given territory or society, but is aimed at demonstrating how we can conceptualise the complex relationships that exist between climate and society. Our representation of this in Figure 4 presents two such models of contrasting detail about a 'breaking point' in relation to the decline of Mapungubwe. Panel (a) shows a simple ecological cause-effect collapse model based on palaeoclimatic data and corroboration from the archaeological record. Here, both the limited consideration of factors and the timeframe of this model result in a pathway more indicative of environmental collapse. By contrast, (b) demonstrates the interactions between the critical components that require consideration when examining climate variability and the decline of the Mapungubwe state. In this more complex framework, the existing work on the region fits into different parts of the model--for example, the environmental setting of the state, the biophysical impacts of climate change on local vegetation, socio-cultural perception of drought and human interaction with the environment in the form of subsistence and livelihoods.

By understanding the socio-environmental context of the society, we can thereafter examine the role of climate and potential impacts of its variability in a more comprehensive manner. Using an interactive model which recognises the non-linearity of complex systems moves away from black-box thinking where society is assumed to react in a set way to outside stimuli. (135) Based on the findings of our synthesis, most analyses lie somewhere between the two models, and it is therefore a key task to integrate what can sometimes be perceived as disparate traditions of enquiry using very different forms of data. Importantly, the model also recognises that 'collapse' can result in opportunity, marked by the rise of Great Zimbabwe and the continuation of the Zimbabwe Culture, but also by the 'buffering feedbacks' noted in Manyanga's counter-evidence for widespread depopulation of the Shashe-Limpopo basin following the Mapungubwe state collapse. (136) Contemporary regional events, such as change in trade patterns, must also be integrated into consideration. A related point often raised is that only those societies connected to the long-distance trade network have evidence for political centralisation in the form of Level-5 and 6 capitals (settlements with the highest number of court levels), and that it was only when the trade arrived at Delagoa Bay that the polities of the northern Nguni became centralised. (137) This offers the prospect of a common dynamic, notably climate and trade, in contributing to pre-colonial state formation. Yet this theory is long-challenged, as such a neatly-packaged view of recurrent factors negates complexity, leaving little room for political process or innovation. On the contrary, ties to external economic spheres involving cattle and ivory may have been unsustainable and resulted in a weakened economic base and a more vulnerable society. (138) Future research can therefore further clarify the interaction of these various dynamics in respect of the vulnerability and resilience of societies.

An important point, however, is that it is easier to draw such schematics than to attempt to describe with any certainty what occurred. (139) The complex model of Figure 4 may fall short of providing complete answers, not least because of data availability, but it allows us to rationally evaluate each of the processes involved within the scope of an expanded knowledge-base. This marks a move towards a more nuanced view of the role of the environment in societal development over the longer-term, rather than the correlation of specific events with contemporary dry or wet conditions. This exercise requires some re-interrogation of the various data, and it is therefore appropriate to finish by providing questions rather than answers. Relating to the arguments of this section, and notwithstanding current data limitations, these include:

* How did climatic 'events' of varying frequency, severity and spatial range affect or erode the vulnerability and resilience of societies?

* What other factors made some societies vulnerable to climatic perturbations and extremes while others were more resilient?

* What role did socio-political and cultural perceptions play in this?

* How did social networks such as trade contribute to mitigate or ameliorate vulnerability to climate variability?

CONCLUDING REMARKS

Through a critical evaluation of the climate-society discourses in pre-colonial southern African state formation and disaggregation, we have reinforced the view that these periods of change are seldom a simple transfer function of climatic or environmental variables alone. Drought or climate variability need not cause food scarcity or famine in well-managed systems, and in each case mediating socio-economic and political factors have been shown to be important. Yet it is equally the case that discounting climate and the environment from the equation due to refusals of climate determinism is unhelpful and misleading. Questioning the relative significance of climate requires a shift, which is already in motion, towards considering the dynamic relationship that exists between climate and society at multiple scales. This pursuit must involve the integration of various bodies of evidence and can, through consideration of the array of factors in Figure 4, provide a basis to assess the role of climate variability in the human past.

Although the defining moments of state formation and decline considered here are clearly of importance, studies should also focus on longer-term interactions. For instance, while there is general agreement that Great Zimbabwe was abandoned during a warmer and wetter period, climate and its variability still interacted with society and state-functioning. Likewise, though warfare on the Zimbabwe plateau from the sixteenth-nineteenth centuries is well-documented and was clearly important, this period was also the coolest and driest period of the LIA, and marks the availability of increasing source material. Re-interrogation of the early-nineteenth century period with the aid of increased proxy-documentary climate data and new approaches is another area where further insights into the complex interplay of environment, society and economy can be gained, adding further nuance to an already substantial body of scholarship. Differences in interpretation will of course remain; however, we can ensure that misleading narratives of the role of climate can be avoided by both acknowledging doubt and contextualising climate alongside a range of human forces. Assembling an integrated analysis of the past is not just an academic exercise, but may also be important for consideration of the future. Examination of the broader historical processes that may have contributed to changes in social vulnerability and resilience can certainly contribute to current debates about climate change. (140) This is not advocating simplistic and misplaced views about history repeating itself, but offering insights into the most pressing issues in present debates where long-term human dimensions are much needed.

ACKNOWLEDGEMENTS

We give thanks to the University of Sheffield for supporting this research, to Karin Holmgren for discussion regarding regional palaeoclimate data, and to the anonymous reviewers for their comments.

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MATTHEW J. HANNAFORD

Department of Geography University of Sheffield, Sheffield S10 2TN, UK and Centre for Africa Studies, University of the Free State Bloemfontein, South Africa

Email: m.hannaford@sheffield.ac.uk

GRANT R. BIGG

Department of Geography University of Sheffield, Sheffield S10 2TN, UK

Email: Grant.Bigg@Sheffield.ac.uk

JULIE M. JONES

Department of Geography University of Sheffield, Sheffield S10 2TN, UK

Email: Julie.Jones@Sheffield.ac.uk;

IAN PHIMISTER

Centre for Africa Studies, University of the Free State, Bloemfontein, South Africa

Email: phimisterir@ufs.ac.za

MARTIAL STAUB

Department of History University of Sheffield, Sheffield S10 2TN, UK

Email: m.staub@sheffield.ac.uk

(1.) Phillipson 1993: 188; Huffman 2009b: 42-45; and Badenhorst 2010.

(2.) Wood 2012. Sinclair et al. 2012 identify Chibuene as the port of entry for trade goods, such as glass beads, from c. AD 750 until AD 1000.

(3.) These culture-history sequences are predominantly based on ceramic style: see Huffman 1970, 1982, 2007: 101-321; but see Sadr 2008; and Parkington and Hall 2009. See also Pikirayi 2001 for Zimbabwe Culture.

(4.) Huffman 2007: 381-400. Extent of farming settlement from Mitchell 2002: 345.

(5.) Palaeoclimate proxy series numbered in Figs. 1 and 2: (1) Holmgren et al. 1999; (2) Holmgren et al. 2003; (3) Stager et al. 2013; (4) Norstrom et al. 2008; (5) Smith 2005, Smith et al. 2007; (6) Hall 1976; Vogel et al. 2001. Note that the precipitation inferences of [delta]18O from speleothem records (1) and (2) have been called into question; however, Fig. 2 shows these to demonstrate previous interpretations.

(6.) Estimates of territorial state size draw from Huffman 2007: 400; population estimates vary but are given in Pikirayi 2001: 123-155; and Huffman 2010b.

(7.) Huffman and Vogel 1991 give an end date of around 1450. Pikirayi and Chirikure 2011 point to documentary evidence for occupation of the site until around the end of the ffteenth century, though state that 1350-1400 was the peak development of the site itself.

(8.) The difaqane is used to allude to events on the interior Highveld, and the mfecane to events originating between Delagoa Bay and the Thukela River involving the northern Nguni, specifically the Ndwandwe, Swazi and Zulu.

(9.) Pwiti 1991, 2005; Huffman 2004, 2007; Sinclair et al. 2012; and Wood 2012.

(10.) Garlake 1973, 1978; and Denbow 1986.

(11.) Phimister 1974; Phimister 1976; Pikirayi 2001: 97-122; Swan 2008; and Huffman 2009b.

(12.) Eldredge 1992; Pwiti 1991, 2005; and Huffman 2009b.

(13.) Huffman 2008, 2009b.

(14.) Beach 1998; and Kim and Kusimba 2008.

(15.) Guy 1980; Connah 2001: 256; and Pikirayi 2005.

(16.) Cobbing 1988.

(17.) For specific examination of climate-society themes see Hall 1976; Ballard 1986; Eldredge 1992; Huffman 1996, 2008, 2009a, 2010a; Tyson et al. 2002; and Holmgren and Oberg, 2006.

(18.) Constanza et al. 2007; Crumley 2007; Butzer and Endfield 2012; and Endfield 2012.

(19.) McCann 1999.

(20.) Tyson and Preston-Whyte 2000: 328-338; and Neukom et al. 2013.

(21.) Ekblom et al. 2011.

(22.) See overviews in Holmgren et al. 2012; Nicholson et al. 2013; and Stager et al. 2013.

(23.) See discussion in Nicholson 2000. The ITCZ is a zone of persistent low tropospheric airflow convergence in the low latitudes. Its disturbances in the mid-latitudes contribute to southern African rainfall.

(24.) Nicholson 2000; Ekblom and Stabell 2008; and Stager et al. 2013.

(25.) Tyson and Preston-Whyte 2000: 305-338; and Sundqvist et al. 2013.

(26.) Nicholson 2000. ENSO influences global atmospheric circulation and sea-surface temperatures. In southern Africa, its El Nino phase induces drought, whereas the La Nina phase brings wet conditions.

(27.) Some instrumental precipitation records were kept from AD 1840 in South Africa, though few were kept before the late-nineteenth century.

(28.) 'i' in Fig 2. draws from the regional palaeoclimate review by Tyson and Lindesay 1992.

(29.) Holmgren et al. 2012 presented an earlier timeline of palaeoclimate data.

(30.) See for example Pikirayi 2001; Huffman 2007: 361-461; and Manyanga 2007.

(31.) Raftopoulos and Mlambo 2009: 1-3. This refects calls to examine different regional groups and their networks of interaction as opposed to states alone.

(32.) Ibid: 1-38. To discuss whether this is a desirable depiction or not is not the focus of this paper, we concentrate on these events as they have been linked with climate variability.

(33.) Huffman 1986, 2007, 2008, 2009b; Pikirayi 2001; Mitchell 2002; and Manyanga 2007.

(34.) Tyson et al. 2000. Other variances of 'Medieval Climate Anomaly' are used in the regional literature and are termed 'Medieval Warm Period' or 'Medieval Warm Epoch'.

(35.) Huffman 1996, 2007, 2008, 2009b; and Manyanga 2007. Badenhorst 2010 differs by stating that intensive horticulture was practised rather than agriculture.

(36.) For discussion of this period, see Denbow 1986; Calabrese 2000; and Denbow et al. 2008.

(37.) Huffman 1986. Huffman 2008, 2009b overviews proximity of settlements to foodplains, while Zhizo settlements were located away from foodplains.

(38.) Huffman 1996, 2007: 384, 2008, 2009b.

(39.) Huffman 2008.

(40.) Raftopoulos and Mlambo 2009: 35, but see Badenhorst 2010: 94.

(41.) Mitchell 2002: 306; Huffman 2008, 2010b; and Sinclair et al. 2012.

(42.) Huffman 2009b.

(43.) Huffman 2008.

(44.) Murimbika 2006; and Schoeman 2006. This approach and ethno-archaeological evidence have been contested, see for example Beach 1998; Bonner et al. 2007; and Marks 2011: 132-138.

(45.) Huffman 1982, 1986, 2007: 325-329.

(46.) Huffman 2008.

(47.) Ibid.

(48.) Huffman 1996, 2008, 2009b; and Tyson et al. 2002.

(49.) Ibid. Huffman 2009a also provides archaeological evidence for drought at this time in the form of burnt structures (daga), thought to be burnt in times of severe drought.

(50.) Huffman 2008.

(51.) Manyanga 2007.

(52.) Mitchell and Whitelaw 2005; Denbow et al. 2008; and Kim and Kusimba 2008.

(53.) Manyanga 2007; and Huffman 2009a.

(54.) Parsons 2007 overviews the migration hypothesis and speculates about a possible Mozambican origin, but Huffman 2004 provides evidence of a northern origin.

(55.) Tyson et al. 2002; and Huffman 2004.

(56.) Huffman 2009b summarises that Mapungubwe and Great Zimbabwe people belonged to separate ethno-historical groups and therefore the move was not a simple power transfer.

(57.) Pikirayi 2001: 123-155; and Huffman 2009b.

(58.) Huffman 2007: 421.

(59.) Pikirayi 2005.

(60.) Ibid.

(61.) Huffman 2009b.

(62.) Pikirayi and Chirikure 2011.

(63.) Ibid.

(64.) Holmgren and Oberg 2006.

(65.) Huffman 2007: 421-425.

(66.) Pikirayi 2005; Pikirayi and Chirikure 2011.

(67.) Pikirayi 2005.

(68.) Beach 1980, 1994; and Huffman 2004.

(69.) Mudenge 1988.

(70.) Beach 1980, 1994.

(71.) Mudenge 1988: 49; and Pikirayi 1993.

(72.) Pikirayi 2003.

(73.) Ibid.

(74.) Beach 1994: 133.

(75.) Eldredge 1992; and Omer-Cooper 1993.

(76.) Gluckman 1960; Omer-Cooper 1966; and Guy 1980.

(77.) Guy 1980.

(78.) Hall 1976.

(79.) Maggs 1984; McCann 2001; and Huffman 2004.

(80.) Hall 1976; and Vogel et al. 2001.

(81.) Ballard 1986; and Holmgren and Oberg 2006. McCann 2001 notes that 'when they plant maize ... peasant families walk a slender tightrope of risk'.

(82.) Ballard 1986.

(83.) Ibid. Note that these severe droughts are not shown in Fig 2 due to low resolution.

(84.) Eldredge 1992.

(85.) Ibid. Others have also ascribed the original stimulus to trade, for instance Smith 1969; and Bonner 1981.

(86.) Huffman 2004, 2007.

(87.) Eldredge 1992.

(88.) Cobbing 1988. Eldredge 1992 countered this with evidence that the slave trade at Delagoa Bay began for the most part after these processes were initiated.

(89.) For example Tyson and Lindesay 1992; and Holmgren et al. 1999.

(90.) See overview of environmental discourses and societal collapse in Middleton 2012.

(91.) Tyson et al. 2002.

(92.) Mitchell and Whitelaw 2005: 240; Denbow et al. 2008; and Kim and Kusimba 2008.

(93.) Huffman 2008.

(94.) Palaeoclimate data and documentary climate reconstruction availability were extremely limited at the time of Ballard 1986; and Eldredge 1992.

(95.) Nicholson et al. 2013 deal with temperature but the same applies for precipitation.

(96.) Sundqvist et al. 2013.

(97.) Stager et al. 2013. Holmgren et al. 1999; 2003 state grey-scale series are measured from the colour branding of stalagmites, originating from downward seepage of meteoric water.

(98.) O'Sullivan 2008; Liverman 2009; Butzer 2012; and Endfield 2012.

(99.) Pfster 2007; 2010.

(100.) Montesquieu 1750, 327.

(101.) Chambers and Brain 2002; Livingstone 2012; and Middleton 2012

(102.) Middleton 2012.

(103.) Hulme 2011 adds that humans are often depicted as 'dumb farmers' passively awaiting their fate.

(104.) Tyson et al. 2002; Huffman 2004.

(105.) O'Connor and Kiker 2004.

(106.) Hulme 2011.

(107.) Beach 1980, 1994; Pikirayi 2001: 52-62; and Huffman 2008, 2009a.

(108.) Hulme 2011; see also Judkins et al. 2008.

(109.) Tainter 2006; Butzer 2012; and Endfield 2012.

(110.) Connah 2001: 256.

(111.) Pikirayi 2001: 154, 2005.

(112.) Berkes and Folke 1998: 9.

(113.) Holling and Gunderson 2002; Redman and Kinzig 2003; Folke 2006; Constanza et al. 2007; Crumley 2007; Pfster 2010 Butzer and Endfield 2012; and Carey 2012.

(114.) Pfster 2007; 2010.

(115.) Nicholson et al. 2013.

(116.) See Neukom et al. 2013. This study used various proxy-documentary archives which have seldom been considered in respect of societal relationships, for example Endfield and Nash 2002; Zinke et al. 2004; Kelso and Vogel 2007; and Nash and Grab 2010.

(117.) Nicholson et al. 2012.

(118.) These data are currently under analysis. See Wheeler and Garcia-Herrera 2008 for overview of climatological data in ships' logbooks.

(119.) Huffman 2009a. Huffman 2010a integrated archaeological evidence for burnt daga--a suggested cultural proxy for drought--with the proxy ENSO record from Moy et al. 2002.

(120.) These data can be obtained from the supplementary material in Brohan et al. 2012.

(121.) Pfster 2010.

(122.) Pfster and Brazdil 2006; Leroy 2006; Tainter 2006; McNeill 2008; and Carey 2012.

(123.) Westerberg et al. 2010.

(124.) Sinclair 2012 following previous examination of the environmental setting of past societies in Sinclair 1987, see also earlier work in Summers 1960; and Hall 1981, 1987.

(125.) Sinclair 1987; Pikirayi 2001. See also Manyanga 2007: 45-46 for critique.

(126.) Jones et al. 2013.

(127.) Ekblom et al. 2011.

(128.) Coombes and Barber 2005.

(129.) Ekblom 2004, 2012.

(130.) Manyanga 2007.

(131.) For example, da Silva Rego and Baxter 1962-1975; Beach and Noronha 1980; Beach 1991; Webb and Wright 2001.

(132.) This approach is demonstrated by Manyanga 2007 in the Shashe-Limpopo basin.

(133.) McCann 1999.

(134.) This approach has been demonstrated elsewhere, for example Dugmore et al. 2007; and has been outlined more generally in Butzer 2012.

(135.) Pfster 2010.

(136.) Manyanga 2007.

(137.) Huffman 2004, 2007: 453.

(138.) See for example Kinahan 2000's findings for the Namib coast.

(139.) Kates 1985.

(140.) Carey 2012.
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