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Transcript of a talk at HEACS Conference on Climate Change, 25 September 2007

Climate Change and the Preservation of Archaeological Landscapes

Richard Tipping, School of Biological & Environmental Sciences, University of Stirling

My brief over the next few minutes is to explore the effects of future climate change on the landscapes and soils of Scotland. Our country is - for its size - prodigiously diverse in its landforms and soils, from exposed mountain ranges in the north and west, made of hard, acid rocks, chiselled out by glaciers in the recent past, covered by nutrient-poor mineral soils, or covered in blankets of acid peat, to the much gentler sedimentary rocks, buried by the deposits of the glaciers eroded from the highlands that underlie the traditionally very prosperous grain-growing lowlands of the midlands and the south. It follows - then - that future climate changes will not impact uniformly across the country - and generalisations in this talk are not easy.

These varied landscapes are not natural - all but the tops of our mountains has been changed - often beyond recognition - by people living and working here for the last 9000 years. There is as much evidence of these past lives in the landscape itself as is found in the archaeological record:

• in the shapes of rivers, for instance - often unnaturally confined to single channels -
• in the broad straths and river terraces, which store and record the products of past soil erosion
• and on the hillslopes, scarred by soil erosion and gullying, denuded of the natural woodlands that would have protected the soil

But of course - these slopes and valley floors also preserve the archaeology itself, in buildings and field systems, sometimes fragmented by recent disturbance but also on occasions in locations where people nowadays infrequently go, where they are astonishingly complete, where every pile of rocks and low turf-wall tells of the work put in to achieve a living.

And lowland and upland peats, because they are waterlogged, preserve the most detailed, yet most fragile, remains, such as the oldest British longbow, made entirely of wood, recovered from eroding peat high in the Southern Uplands. Away from the peat it would not have survived - but perhaps ironically given our topic this afternoon, only found because the peat was eroded in the last period of climatic deterioration, the 'little ice age'.

Are these archaeological landscapes, often preserved for thousands of years within and on soils and peats - under threat from future climate change?

We need to remember that future climate change is much more than 'global warming'. The changes involve:

• some increases in temperature - though this is least for maritime regions of Europe such as Scotland
• substantial increases in precipitation - perhaps 1-2% more per decade - but marked differences between a much wetter west and a less wet east
• changes in the intensity of the seasons
• probable increases in the frequency of extreme events like storms and freak rainfall events, and possible increases in their magnitude

These factors sometimes combine in positive feedbacks that make the consequences worse, and sometimes combine in negative feedbacks to neutralise the worst excesses.

These changes will affect soils and the processes working on the landscape, and so will impact in turn impact on the preservation of archaeological structures and artefacts in and on the soils. I'll select the particular changes that may have impacts on how we might use the landscape, because the threats to our archaeological heritage will mostly come through land use change.

Some scenarios posit complex decision-making changes. For example:

• increasing soil moisture makes soils wetter for longer in the year
  • this increases the pressure to prepare the ground for crops
  • this increases the likelihood that ploughing happens when the soils are too wet
  • this leads to soil compaction and the loss of soil structure
  • this may result in damage to archaeological remains in the soil
• because temperatures will rise, and grasses will grow better because the growing season is longer, upland soils used now only for rough grazing may be used for more intensive livestock production, increasing damage to archaeological structures through trampling and poaching of soils
• where precipitation increases, soil erosion may be increased - creating gullies like this one - but temperature increases will also lead to more luxuriant plant growth, and this will stabilise soils on some slopes. So vulnerability to soil erosion will depend on land use as well as the distribution and intensity of rainfall.

Peat soils are more complex in their response to climate change. Increasing temperature and carbon dioxide in the atmosphere leads to increased decay, and so the peat loses internal structure, impacting on buried artefacts, but increased precipitation leads to less decay, so again this threat will depend on where the peat is in Scotland.

Soils and peats are components of landscapes. Subtle changes in these may lead to threats to the archaeological resource. My view on these impacts on soils can be summarised:

1. the effects of increasing mean annual temperatures will - in much of Scotland - frequently be nullified by increasing amounts of rainfall
2. most of these threats to the archaeological resource will come from changes in land use - these threats are not generally direct consequences of climate change
3. most important - it seems to me - is that climate-mediated changes only add another layer of complexity to our existing, long-understood and accelerating threats to the resource, from agricultural change to forestry, to urban development and commercial peat-cutting. We should not lose sight of this. These threats remain much more tangible and relevant issues.

I think - however - that a greater threat to the landscape from future climate change comes in its very unpredictability - in the impacts of extreme events. These are by their very nature the hardest effects to predict, because they are rare. This is why commentators handle with caution, questions about whether this year's floods in southern Britain, or disasters like Hurricane Katriona, or the Lochearnhead rockslide of August 2005 - can be explained by climate change. As the statistics of extreme events becomes more refined, we can start to see that these extremes will be more frequent in the future. They probably won't become normal - and they will thus remain news-worthy - but when they happen, their impacts on the landscape will be destructive.

I will briefly explore in the final part what these changes might mean for the destruction of the archaeological resource buried within or lying on valley floors. These are large accumulations of riverine sediment, common in lowland areas of Scotland where the densest populations have always been. People have always used these valley floors, sometimes settled on them, and often deposited things in them. Because these valley floors fill up over time in layers of sediment, sometimes we can find prehistoric landscapes sealed and preserved in superb detail. We understand little of these buried landscapes in Scotland because (1) archaeologists don't routinely look in quarries where the sediment is being extracted, and (2) because urban spread onto floodplains is less here than in England.

However, valley floors are also peculiarly vulnerable to climate change because nearly all the water added when rainfall increases runs off to the rivers. And the rivers get bigger and less controllable. Sometimes the only consequence is flooding (I say "only" not to be flippant). In the context of our topic this afternoon, flooding is protective of buried archaeology by adding another layer of sediment. Major climate changes can lead to the complete destruction of floodplains. We are beginning to recognise that the last few decades have seen changes comparable to those in the more distant past, when valley floors have been eroded and removed by rivers. We may not be able to rely on engineering solutions for protection. We need to record and monitor the hidden archaeology on and within our valley floors in much the same way that Tom Dawson will show how we are monitoring our eroding coast, or an archaeological resource we don't yet understand may be lost.

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