Global warming

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SITES (2002) volume

5 pages



Global warming The implications for sustainable archaeological resource managell1ent P. CHAPMAN

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ABSTRACT Global warming is recognised as an important environmental, and consequently political, issue. Ristng global temperatures have demonstrated the potential for raising sea levels and increasing surface temperatures, with wide-reaching implications for habitats and biodiversity. While this remains high on the priority list for ecological sciences and coastal management, the implications for archaeological resource management remain unexamined. This is surprising given the increasingly close relationship between ecological and archaeological site management. This paper aims to focus attention on the issue of archaeology and global warming, and presents an outline of the possible consequences and approaches that may be considered, particularly in relation to the archaeology of wetlands. INTRODUCTION

Accu- Weather, a leading commercial forecaster, has suggested from ground-based monitoring that there has been a global increase in air temperature of about 0.45 degrees Celsius over the past century [1]. It is widely accepted (though still fiercely debated) that the planet is warming, and that the effects of this process may be seen with the increase in environmental disasters and extreme weather events. Given these factors, the implications for the management of archaeological sites and landscapes are likely to be far-reaching, though they remain poorly understood. In 1999, Klaus Topfer of the United Nations Environment Programme (UNEP) noted that 'climate change is already happening' [2] . The reasons for this remain in debate, although a significant factor seems to be through anthropogenic activity, and particularly through emissions of' greenhouse gases' such as carbon dioxide, a by-product of burning fossil fuels. Greenhouse gases, which are also generated naturally, effectively reduce the ISS:\ U:;0-:;055



planet's ability to reflect heat, retaining it inside the atmosphere. The principal scientific driving force concerning global warming is the Intergovernmental Panel on Climate Change OPCC), established by the World Meteorological Organisation (WMO) and UNEP. The IPCC provides the principal advisor to the Conference of Parties (COP) to the United Nations Framework Convention on Climate Change (UNFCCC), and has generated a number of reports that form the backbone of current models of climate change and global warming. A report by the IPCC [3] stated that the rate of global warming might be higher than previously expected, with models indicating a global temperature increase in the region of six degrees Celsius by 2100, indicating an average rise in sea level of 0.95m and a northward migration of habitat of c. 500km. It has been predicted that even with a stabilization of greenhouse gas emissions, sea levels would not stabilize until 2025 [4, 5], A series of meetings by the United Nations aimed at countermeasures has highlighted the potential

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environmental threats. The first of these was the United Nations Earth Summit in Rio, which took place in 1992 and highlighted the threats to the planet and the need to reduce emissions of greenhouse gases, but the resulting recommendations were not legally binding. In December 1997, a further meeting in Kyoto resulted in the 'Kyoto Protocol', the agreement of UNFCCC [6], Consequentlya number of meetings have taken place that have explored ways in which industrial nations may reduce their emissions of greenhouse gases. However, the Kyoto agreement was rejected by the USA, who recently announced (February 2002) that they are devising their own goals relating to greenhouse gas emissions. Whatever the causes of increases in global temperatures, the potential effects may be devastating. Two principal factors may be identified as having direct significance locally: sea level rise (through thermal expansion of ocean water and melting of ice caps and glaciers) and increase in temperature. A recent report by the World Wide Fund for Nature [7] presented the results of a study aimed at investigating the impact of these factors on biodiversity using both climate and vegetation models. It was argued that increases in temperature would necessitate the movement of plant and animal species in order to maintain their ecological requirements. Required migration rates (RMR) generated by increasing temperatures would be higher than most species' actual migration rates. Indeed, it was argued that the rate of increase would be greater than that experienced during other periods of major climatic change, and that the RMR for plants would be approximately ten times higher than those recorded for the Devensian period - the most recent period of massive natural climate change. It was noted that this, in addition to barriers to terrestrial migration (e.g. rivers, lakes etc.), might result in the extinction of many species. This problem is further emphasised by the effect of natural and anthropogenic boundaries to migration such as rivers, dikes or even land use [SL However, problems with the statistics from the various research avenues remain tempered by politics, often being commissioned by particular special interest groups, and should therefore be considered within context due to the potential for interpretation bias.


Despite the high media profile attributed to issues of climate change, references to it within the archaeological literature are rare. The effect of rising sea level particularly, and the resulting increase in levels and rates of erosion, has been highlighted for its damaging effect on buried and partially exposed archaeological remains, and has been mentioned previously in relation to its threat to coastal resources [8]. The issue has also been raised in terms of threats to archaeology more generally, for both wet and dry sites, within a study aimed at assessing the overall threats to wetland archaeology across England [9], The potential for a drier climate and its implications for wet preservation, in addition to the threats of extreme climatic events, has also been highlighted [10], However, its mention within strategies for management is cursory, emphasising the value of the resource in understanding climate change, rather than the future threats to it [11]. So what are the implications for archaeology, specifically wet -preserved sites? The direct implications of the apparent trend of global warming on archaeological resource management appear at first to be limited due to the long timescales involved and the presence of more immediate. management concerns, such as local impacts including flooding. However, the primary, longerterm effects of climate change are in fact the more significant and present a range of potential problems. For example, the case within wetland archaeology is particularly crucial because the fragile organic remains that are often preserved, in addition to their burial enVironments, require a certain degree of stasis in order to be sustainably preserved in situ [12], The effects of global warming indicate change, and consequently instability which will disrupt the conditions for in situ preservation, and therefore for site management. The often-cited trend of sea level rise has certain implications for archaeological remains. Tidal influences affect both coastal zones and large reaches of river systems. The consequences of sea level rise have been demonstrated with increased chances of terrestrial flooding as rivers become backed up, resulting in the need to manage the erosion of coastal areas. A number of techniques are currently


used, including the short-term solution of direct barriers, and longer-term management through what has been previously termed 'managed retreat'. This process aims to move flood defences inland in order to allow coastal areas to flood so that the flow of water is not impeded [13].


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It has been noted previously that coastal erosion is one of the primary impacts from sea level rise [4, 14]. Archaeologically, the value of the coastal! intertidal resource has been emphasised previously [15, 16], although the definition of this 'coastal! intertidal' area may be called into question. For example, the coastline has changed through time and the archaeological deposits under threat include those within the intertidal zone in addition to those either side of it (including wrecks). The devastating and varying effects of erosion on the archaeological and palaeoenvironmental resource in these areas has been demonstrated previously [17], and have also resulted in the discovery of such high-profile sites as the Ferriby boats [18] and Seahenge [19]. These sites raise further management issues concerning erosion since these processes also reveal new archaeological sites in addition to ultimately destroying them and their environmental contexts. Furthermore, through inundation, newly flooded areas will alter patterns of drainage, creating channels within the new intertidal zone that will have a potentially erosive effect on archaeological deposits [cf. 10], Erosion may be exaggerated through changes to channel flow patterns that create sediment erosion and accretion throughout coastal and river systems. The results of this will be a complex and extremely unpredictable pattern of erosion and subsequent damage to any buried archaeological resource.



tidal areas are those within eroding sediments. While this does not necessarily present a direct threat to archaeological deposits, it does present a problem for their management. This is a clear issue when dealing with submerged landscapes [21]. An additional effect of continued accretion over longer time periods is the development of new landscapes and, consequently, land use. In these cases the locations of known sites need to be recorded in three dimensions for their future management.

Changes to the burial environment An increase in flooding of coastal areas presents the possibility of altering groundwater chemistry primarily through the introduction of brackish water [22]. Furthermore, this will alter the vegetation in favour of saline-tolerant plants [cf. 23] causing further changes to the burial environment. A preference for preservation in situ as a management plan has become increasingly common in government policy [e.g. 24, 25, 26], The in situ preservation of archaeological remains requires a degree of generic stasis in the burial environment. In other words, factors that increase destruction rates are those that induce change, be it from the actions of moles, worms, fungi, bacteria or the movement of water. Alterations to the environment at all resolutions provide changed habitats and the loss of some species and the gain of others. This type of change in relation to global warming has been identified with a reduction in wetland productivity and function [27],and this may be considered in relation to altered nutrient status [cf. 28]. Whether biological activity is reduced or enhanced through global warming, change will be introduced to the burial environment, and this holds the potential for damaging buried archaeology and palaeoenvironmental deposits [12].

Local climate Sediment accretion The antithesis of sediment erosion is accretion. It is possible for archaeological deposits to become buried beneath many metres of accreting silts [e.g. 20], The consequence of this is twofold, with both known sites becoming concealed, and the potential for discovering new sites diminishing. It is perhaps ·no coincidence that the major discoveries of inter-

Local changes to conditions include increased wetness and increases in temperature. RMR have already been mentioned as a consequence of this, but there are other factors. For example, an increase in temperature in higher latitudes increases biological activity [5]. At the microscopic level, this may cause the re-introduction of microbial activity, thereby inducing new processes of degradation, particularly

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of organic archaeological remains. Furthermore, local changes will influence the hydrological cycle due to interruptions to seasonal weather events and patterns of precipitation, evaporation, transpiration, runoff, groundwater recharge and flow. This will alter the recharge of aquifers and will influence water quality [5].The implications for archaeological deposits are far-reaching. Changes in the availability and chemistry of groundwater will have an especially direct effect upon wet-preserved sites [cf. 12]. This is of particular concern given the seemingly invisible nature of such changes that might covertly alter preservation without it being noticed.

Links with nature conservation

resource, as for other environmental resources, remain ill understood. This presents potentially large problems for the future of site and landscape management. However, there are a nun1ber of ways that may be considered advantageous for addressing this threat. Primarily, monitoring needs to be conducted with regard to archaeological sites. This issue has already been addressed in relation to understanding and limiting decay processes on wetland sites le.g. 12]. Such approaches need to be developed in order to understand change within the burial environment and need to include a range of monitoring parameters. The results from such monitoring need to be calibrated against ecological and meteorological models in order to assess how long-term changes in global conditions are affecting the burial environment. Furthermore, the integration of archaeological issues with habitat creation and predictive habitat creation needs to be addressed to ensure that the maximum benefit is gained from all researchers working within this field.

There have been increased trends in the development of liaison between archaeologists and conservationists in the management of landscapes. The need for this has been noted previously [29]and has since been demonstrated [30]. For example, at the site of Sutton Common in South Yorkshire, UK, liaison between archaeologists, conservationists and a significant number of other parties has united their interests of re-creating a natural wetland environment, with habitat benefits, with the in situ preservation of wet-preserved organic archaeological remains [29,30].Similarly, within the Somerset Levels in western England, and at Shapwick Heath particularly, the integration of archaeological in situ preservation has been coupled with nature conservation involVing a large number of organisations [10]. Current debate about the consequences of global warming on the management of National Parks and areas of managed haoitats is ongoing. In principle, trends might include the development of habitat creation in advance of migration in order to mitigate for the problems with the RMRof different species leI 7]. The intrinsic links that are developing between archaeologists and other environmental concerns brings archaeology into such debates.



] ames Cheetham commented on an earlier draft of the text.

The principal problem for archaeological resource management presented by global warming lies in the many uncertainties about the future. Various models predict various outcomes at various temporal rates. Even if rates of change were understood, the exact effects on the archaeological

Henry P Chapman PhD MIFA is a Research Fellow with the Wetland Archaeology and Environments Research Centre at the University of Hull, specialising in technical survey and GIS applications in archaeological interpretation and resource management.


This paper has aimed at highlighting the potential issues generated by trends in global warming that may affect archaeological resource management Currently our understanding of global dynamics remains limited, and this is partially due to limitations on the length of time of monitoring. Within archaeology monitoring of sites needs to begin now, perhaps in collaboration with other monitoring projects, to ensure the best chance of understanding a history of environmental change and its effects upon the burial environment. Theories and models may change through time, but the data collection needs to begin now.


Contact address: Wetland Archaeology and Environments Research Centre, University of Hull, Hull Hu6 7RX, UK. Tel: + 44 1482466064. Fax: + 44 1482 465362. Email: [email protected]


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