Climate in the Iron Age

[Brennus]

The climate was not as different as today. During the Late Bronze Age and Iron Age there were two major climate fluctuations. The first of these c.1000/800BC resulted in a cooling of the climate. Along the Atlantic seaboard this had the result of producing a wetter climate which in turn resulted in many of the marginal, upland settements of Britain and Atlantic Gaul being abandoned. It is quite likely a similar thing happened in Ireland, although it is quite difficult to be sure as, following the end of the Bronze Age (c.1000BC Western Europe, c.800 BC Britain, c.600 BC Ireland) the Irish settlement record becomes as scant as a stripper's clothes. Palyonological data from Irish peat bogs does show a regeneration of tree coverage around this time, which has been interpreted as indicating a decline in population and shift to pastoralism as a result of climate change. The same climatic change does not really appear to have impacted on Scandinavia or Western Iberia, and both areas show a great degree of settlement continuity until effects of the Romans become felt much later in those areas.

Around c.300BC there was an improvement in climate and temperatures rose which appears to have resulted in an expansion of agriculture across north western Europe. In Britain we can detect an expansion of field systems in the south, as well increased levels of wheat being cultivated. In Ireland we also see the introduction and subsequent develop of a localised form of the La Tene culture, as well as several major earthwork and structural constructions such as the Black Pig's Dyke and Emain Macha in Ulster, all of which would have required a larger, more centralised population than appears to have existed in the earlier Iron Age. In Northern Gaul there is likewise an intensification of agriculture (although French archaeologists will tell you this is because the Belgae arrived at this time rather than being the result of a warmer climate) whilst in the Netherlands the old grabenfelt cremation culture ends and we see people begin to move to much more permanent settlements with expanded agriculture. A similar process can be detected in Jutland around a century or two later. Likewise in central and southern Gaul, c.200BC, there is a major expansion in the number of farmsteads, which can be explained as being the result of a population expansion based on increased food production which in turn can be linked to a warmer climate.

During the Roman period there does appear to have been a degree of anthropogenic global warming. Roman industry was on a much larger scale than much of the indigenous industry which it replaced in western Europe (although exceptions such as central Gaul exist). For example in Iberia and western Britain huge lead mines were opened up. Recent research has suggested that in excess of 50% of the timber grown in the Roman Empire was used as fuel and Roman sites like Pompeii have found massive amounts of charcoal. Likewise the Romans also developed industrial scale charcoal producing sites (which you need if you have cities like Rome and Capua). All of this contributed to further global warming. By late Antiquity, however, it seems this warming was having similar affects to the climate change we are observing today, with the Gulf Stream being put out of place resulting in a return to a wetter, cooler climate. Around this time (although due to a variety of social reasons also) there was a decline in agricultural output and population decline.