Thousands of years ago, Britain and Ireland experienced a series of population booms and busts. These have been attributed to cycles of population growth over-straining natural resources. However, a more detailed study has called this into question, revealing that the crashes coincided with changes in the North Atlantic climate. While modern technology has allowed the islands to support a once unimaginable population, the work might still have something to say about future vulnerability.
Archaeological evidence of cereal crop growth first appears in Britain around 6,000 years ago. According to Professor Andrew Bevan of University College London, this was associated with a rise in population that was so sharp, it must have been at least in part the result of migration, rather than increased birthrates or improved survival alone. Between 5,500 and 5,000 years ago, however, the population fell, before rising to a peak 4,000 years ago, followed by three more rounds of fall and rise.
Comparisons between the Roman era and what went before and after are difficult, as archaeologists have used different methods to study this period, but post-Rome populations were similar or lower than in the previous high points, and even these numbers look good compared to the Black Death and several centuries thereafter.
However, the region was not a single undivided nation at any point in this time and migrations were not made lightly. By comparing the populations of South-East England, North West England/Wales, Scotland, and Ireland as four independent sequences, Bevan was able to find both similarities and differences in population patterns. When one region was out of step with the others, Bevan argues in Proceedings of the National Academy of Sciences, internal factors could have been responsible, but synchronized declines must have broader explanations.
Notably, the declines coincide with periods of salt enrichment of the Greenland Ice Sheet, something attributed to increased stormy conditions in the North Atlantic, which probably didn't favor farmers. This is consistent with shifts observed in traces of wheat and the less productive, but hardier, barley. Barley was often used as a desperate substitute crop after wheat planting failed.
These storms are in turn thought to have been associated with periods of reduced solar output, which may have benefited tropical regions, but would have been deeply unfortunate at high latitudes.
Britain and Ireland provide an exceptional window into the ancient world because they have been so extensively studied. This paper drew on a database of radiocarbon dating of 30,000 samples across the islands. We can't yet say how typical the findings are for other parts of the world, but the work favors those who see climatic change as a major factor in the decline or even collapse of ancient societies, and fear the implications for ourselves.
