Using peat to explore the impact of climate change

The abandonment of environmentally fragile Irish uplands like Slieveanorra – a remote site with a small raised bog – has previously been linked to socio-economic problems driven by climate change.

Peatlands – wetland landscapes with distinctive soils composed of slowly decaying organic matter (see ‘For peat’s sake’, CA 380) – have remarkable preservative qualities, and in Britain and Ireland their waterlogged depths have yielded archaeological finds from prehistoric wooden idols (‘News’, CA 380) to naturally mummified human bodies (‘Touching the past’, CA 375). As well as preserving the buried remains of past cultures, though, peatlands function as stores of carbon and palaeoenvironmental data, formed over several millennia. This has led Dr Gill Plunkett and Professor Graeme Swindles from the School of Natural and Built Environment at Queen’s University Belfast to analyse a peat core from Slieveanorra on the Antrim Plateau in north-east Ireland (below) in order to investigate the impact of historical environmental change on the area’s population over the last 1,000 years.

Image: Gill Plunkett.

The study (published in the open-access journal PLOS ONE, covers two broad periods: the ‘Medieval Climate Anomaly’ (c.AD 950-c.1250), when Europe experienced warmer temperatures, and the ‘Little Ice Age’ – a time of cooling and climate fluctuation between c.1250 and c.1850. Ireland suffered numerous crises across these centuries: the European Famine (1313-1317), the Black Death (c.1350), the Irish Famine (1740-1741), and the Great Famine (1845-1852; also known as the Irish Potato Famine). The abandonment (in prehistory, for example) of environmentally fragile Irish uplands like Slieveanorra – a remote site with a small raised bog – has previously been linked to socio-economic problems driven by climate change, but Gill and Graeme caution against perceiving the area as a necessarily vulnerable place. ‘In the face of environmental change, not all human communities respond the same way, and how well a community can respond is largely linked to social conditions of each respective population,’ Gill said.

The presence of abandoned dwellings and field and drainage systems in the immediate vicinity of Slieveanorra Bog (within 0.6km) is testament to previous occupation of the area’s valleys since at least the early 19th century, while 19th- and 20th-century documentary sources indicate that the area was populated by a handful of farming families during this later period. A full history of the area, however, is not available based on archaeological and historical records alone – and so, to map the relationship between past climate change and human activity around Slieveanorra over the last millennium, the scientists combined analysis of the peat core with an examination of local microbial and organic data, and related historical documentary sources. The results of these investigations were dated using radiocarbon dating as well as historical volcanic ash markers from within the peat core itself, which allowed the researchers to work to a high degree of temporal precision when analysing the palaeo- environmental data in its historical context.

The research indicates that the remote community of Slieveanorra remained resilient in the face of climate change, natural disasters, and extreme weather events. Pollen analysis, for example, revealed evidence for the long-term cultivation of crops and the gradual decline of woodland near Slieveanorra Bog, which the scientists interpreted as proxy indicators of nearly continuous occupation of the surrounding uplands between the late 12th and early 20th centuries. Only one major break in occupation was detected at the site, during a wet-climate period in the mid-15th century. This decline coincides with the later stages of a phenomenon typically referred to as ‘the late-medieval crisis’ – a period of economic decline and woodland regeneration following widespread population crashes in the 14th century, often said to have been exacerbated by the deteriorating climate of the Little Ice Age – but the researchers have managed to differentiate the 15th-century downturn at Slieveanorra from earlier events using their highly refined chronology.

Indeed, while pollen records from elsewhere in Europe show evidence of forest regeneration indicative of a decline in population following the Black Death, neither this event nor the medieval European Famine appear to have disrupted the level of land-use around Slieveanorra, which actually appears to have increased from the 14th century. The temporary 15th-century decline in activity at Slieveanorra, moreover, appears only to have lasted one or two generations: the researchers found evidence for the resumption of farming around the turn of the 16th century, and for the community’s persistence through colder climates into the 17th century. Gill and Graeme did, however, detect brief reductions in land-use coinciding with 18th- and 19th-century famines, but, significantly, neither of these events caused the area to be abandoned. Rather, the Slieveanorra community seems to have endured through to its eventual decline in the 20th century, despite the various challenges of the last millennium and contemporary climate fluctuations.

Previous research has drawn causal relationships between climate change and societal disintegration throughout history, but Gill and Graeme’s work challenges the generalising tendencies of broader narratives that attribute historical societal collapse to environmental crises. ‘These results reflect a community that was able either to escape the effects of environmental change, or to rebound quickly,’ Gill said. ‘This surprising resilience from a relatively remote occupation was likely the result of social and economic factors – such as broad-based farming practices and cottage industries – which made the community flexible and adaptable.’