Palaeoclimatologists reconstruct past climatic conditions (mainly temperature and precipitation) using a number of high-resolution ‘proxy’ records. The records that are produced can then be assessed, in comparison with archaeological findings and historical records, to examine the impact of past climate change on the human race and individual societies. In a recent newspaper article titled “The climate has changed before: But this is different – look at the archaeological record”, Peter Campbell highlighted the importance of this line of research to the climate change debate. The value of this methodology and archaeology as a whole to the climate change debate is currently undervalued and a series of posts on this blog (this being the first) will argue it’s significance.
These ‘proxy’ records of palaeoclimatic variability are named so as they are not direct recorders of climate, such as modern-day weather stations, but instead host a residual signal of past climate in their structure. Such archives include sediment cores, tree rings, stalagmites and, perhaps the best-known example, ice cores. The data held within these archives is extracted using a variety of different analytical techniques. For stalagmites, samples of calcite dust (the mineral from which they are formed) are drilled out and chemically analysed to identify changes in their composition that correspond to local changes in precipitation or, more rarely, temperature.
Humans like you and I, Homo sapiens, have been around for c.200,000 years. As a species, we have lived during two climatic epochs, the Pleistocene (2,700,00-11,700 years ago) and the Holocene (11,700 years ago – present). The latter witnessed the most important innovations in human history. These include: agriculture, writing, industrialisation, the international space station and many more. Climatically, the epoch can be separated from its predecessor by warmer temperatures and a much more stable climate. This relative stability is considered by many a prerequisite for the cultural and technological boom of the Holocene. As higher resolution palaeoclimate records have been discovered, it is becoming ever more evident that, although not to the same scale as the Pleistocene, variations in climate did occur. When climatic variations are compared to archaeological and historical data, correlation of change is often found.
As Campbell mentions, past climatic variability has been used by the Trump Administration to say that “climate has changed and is always changing”, and I cannot fault what they have said. The climate has changed and is always changing, the only difference now is that human actions are exacerbating this change to a scale never before witnessed.
Current projections put global average surface warming by the end of the century (without the introduction of drastic counter-measures) between 1.8 and 6.4°C. However, the current ‘global warming’ that we are used to hearing about is actually a much more complicated phenomenon than previously thought. Climate change is now considered the scientifically accurate term, as NASA explained – “changes to precipitation patterns and sea level are likely to have much greater human impact than the higher temperatures alone.” An increase in summer temperatures is now believed to result in colder winters due to feedback systems related to increased sea ice melt.
Surface warming projections from the IPCC
During the Late Antique Little Ice Age (536-660 CE), winter temperatures are known to have dropped by up to 2°C. This change had a dramatic effect on many societies worldwide, and many were forced to transform their lives in order to survive. Colder temperatures enabled the transmission of the Justinian Plague from Ethiopia to Constantinople, as temperatures between these two regions were normally too high for fleas carrying the disease to survive. One-fifth of the city’s population perished in three months. In China, the Northern Wei Dynasty was driven to collapse by the over-taxing of farmers and a consequential lack of trust in central government. The taxation arose in response to decreased yields caused by the colder climate.
As climate becomes more variable worldwide, periods such as this may become analogous to the modern world: political unrest, unfruitful farming and large-scale migration will become a reality. The advantage we have in the modern-day is that we have both the foresight to predict what’s coming, and hindsight, enabling us to learn lessons of resilience from the past.