Digging up art
Bronze bog hoard
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Editor Mike Pitts
under the weather
Sebastian Payne, chief scientist at English Heritage, ponders climate change and preservation of archaeological remains
Climate change is in the news. The past ten years have been warmer than any other decade since records began (some 300 years ago) as climate modellers predicted. This is a high-priority issue for the government (though our commitment to cut carbon emissions and fossil fuel use sits oddly with recent pleas for OPEC to increase oil production). However, plans to drill a deep ocean core on the Lomonosov Ridge in the Arctic1 to look in greater detail at climate change over the past 50 million years, remind us that the subject is still poorly understood. One of the purposes of the Lomonosov project is to gather more evidence about predictions that another Ice Age is due fairly soon (in geological terms!): it can get colder as well as warmer.
Climate change comes as no surprise to prehistorians. They are very aware of preserved glacial valleys and moraines from past Ice Ages, and of the bones of animals like hippopotamus and elephant from intervening warm periods – hippo bones were found in interglacial deposits below Trafalgar Square.
Over the past few thousand years climate has been fairly stable, but we see changes reflected in the record of settlements in marginal areas. The Little Ice Age, with a cold peak from the 16th to the 19th century with ox-roasts on the frozen Thames, caused the abandonment of Scandinavian settlements in Greenland and frequent famine in marginal areas in northern Europe.2 Documentary evidence (Domesday Book lists 46 vineyards in southern England) and insect remains from English sites suggest warmer conditions at some times in the Roman period and again in Medieval times. Bronze Age settlements, farms and fields in upland Britain, now often covered by bog, were abandoned because of cooler wetter conditions at the end of the Bronze Age.
Research on past climates and environments also gives us a longer perspective on present world climate. Knowing the earth’s climate has varied widely and changed rapidly in the past, helps us understand that climate change is normal; archaeological and palaeoenvironmental evidence for past conditions gives us a longer record against which to assess climate change predictions.
Environmental and climate changes also have obvious impacts on the preservation of archaeological sites. Drainage and water abstraction already damage wetlands – peat deposits with all that they can tell us about past environments. Our sinking coast in the south-east is eroding: in Essex Neolithic sites such as the Stumble, with well-preserved cereal remains, are now in the intertidal zone. These have been a high priority for investigation for some time. Coastal realignment and managed retreat are adding to what needs to be done.
Current predictions for the UK include temperature increases of 2-5°C by the 2080s, sea-level rise of up to 80 cm, slightly wetter winters and drier summers and, with lower confidence, increased storms. While there is some inevitable uncertainty, predicted changes add to the urgency of work on waterlogged and coastal archaeology, as set out in a pilot study undertaken for English Heritage by May Cassar at University College London.3
There are important implications also for the policy of archaeological preservation in situ (as was considered but rejected, for example, for Seahenge). We know surprisingly little about the effects of environmental change on buried, especially waterlogged archaeology. Climate change impacts make it all the more important to find out more about where preservation in place is likely to work and where it may not.4
1 Times June 4, Arctic trip may predict ice age
CBA web:Jan/Feb 2005