Climate Lessons From The Societies Past

Charles Lyell’s Principles of Geology, published in the 1830s, introduced the famous maxim, ‘The present is the key to the past’. This deceptively simple statement carries a powerful meaning that the processes occurring today have operated throughout most of the Earth’s history. Its message is – learn the present-day processes; you will understand what happened in the past. The current climate challenges compel us now to open a new major frontier that requires us to use past events to prepare for the future. The past, thus, becomes the key to the future.

For the first time in geological history, as a direct consequence of human activity, the rising level of greenhouse gases is accelerating global temperatures, leading to extreme weather events and rising sea levels that could inundate enormous cities. The past is always there to offer us precedents, which though caused by natural factors, unlike the present, might provide some pointers on dealing with what is predicted to be a crisis-ridden future.

In the book Collapse, published in 2004, Jared Diamond explores how societies choose to fail or survive in the face of climate adversities. Among many factors, the society under duress will win or lose depending on its response to its problems. Past climate records retrieved from archaeological and historical records or information preserved in deep-sea sediments, ice cores, tree rings, or cave deposits, can be interpreted using science. This type of data shows how humanity survived intense periods of ice ages in the past 730,000 years.

Adapting to the changes in the climate

After the last ice age, the Earth entered a warming period and our ancestors adapted to this change in climate very skilfully and eventually laid the foundations of the pre-industrial agriculture-based civilisations along the valleys of the Indus, Nile and Tigris-Euphrates rivers, even while adapting to the intense periods of droughts and flood, often at a heavy cost in lives and destruction. It sometimes lead to the decline of settlements, which compelled survivors to migrate over land and sea in search of habitable environments. In this context, it is relevant to discuss how climate change drove the early Harappans, builders of one of the earliest civilisations, to abandon the Indus Valley and migrate closer to the hills in the north.

The Harappans flourished in the Indus Valley, now part of Pakistan and northwestern India, by establishing sophisticated urban centres and engaging in long-distance trade with the Middle Eastern settlements. Their shift from urban traders to rural agrarians began approximately 3,900 years ago. Changes in the summer monsoons prompted the Harappans to relocate closer to the Himalayan foothills, drawn by the more intense winter monsoon that activated minor rivers (such as the Ghaggar-Hakra, also known as Saraswati) and moved towards the Ganga basin, where summer monsoon rains remained consistent. This transition resulted from a climate-induced decline in the summer monsoon, affecting the cyclicity of the Indus river floods that inundated the farmlands.

The final blow to the Harappans was the decline of the winter monsoon between 3,300 and 3,000 years ago, caused by the weakening of the Westerlies from the Mediterranean Sea. Consequently, the seasonal rain-fed rivers dried up, leading to the collapse of rural Harappan settlements. The weakening monsoon in northwestern India likely resulted in the expansion of grasslands in that region, encouraging the Indo-Aryan pastoralists to settle initially in the Indus Valley as they crossed over from Afghanistan, who were escaping from Central Asian steppes which were undergoing deep winter freezes and progressive aridification. The dryness of the Indus Valley region encouraged these pastoralists to expand toward the Ganga basin. Equipped with iron technology, they could transition into agriculture-based communities by clearing forests.

A lesson on how a marvellous civilisation disappeared because of its low adaptability quotient can be learnt from the ancient Mayans, who thrived from 2000 BCE to 950 CE. They inhabited what is now southern Mexico and northern Central America, constructed thriving cities, developed intricate calendars and hieroglyphic writing, and were renowned for their accomplishments in mathematics, agriculture, and architecture. However, by the end of their classic period, around 900 CE, these cities were abandoned and deserted. Among various contributing factors, paleoclimate studies that analyse carbonate cave formations (speleothems) indicate a drastic reduction in rainfall, culminating in the Great Mayan Drought, which was the final blow to the classic Mayan civilisation that extended from 250 CE to 950 CE. The new studies reveal that parts of Mesoamerica where the classic Mayan civilisation thrived were impacted by the Medieval Warm Period (MWP) – an interval marked by warmer temperatures and lower precipitation. Although not a globally synchronous event, the MWP was caused by increased solar activity and changes in ocean circulation.

The Mayan civilisation lasted for about 3,500 years, peaking in cultural achievements during the early medieval period, with its decline coinciding with a severe drought. Why did such a massive population of millions of Mayan descendants vanish? Jared Diamond endeavours to address this question in his book Collapse. The droughts must have significantly diminished resources, leading to starvation, thirst, or conflicts over increasingly scarce supplies. Additional environmental factors include deforestation, soil nutrient depletion, and excessive cultivation, which eroded hill slopes and resulted in soil loss. The history of the Mayan civilisation illustrates how societies faltered in times of crisis, particularly during drought and other climatic disruptions with dire existential implications.

The numerous unsettling parallels with present times – population growth surpassing available resources and people battling over dwindling supplies of resources, should worry us. Climate history also highlights passivity or lack of foresight among the leaders (kings), which hastened the collapse of ancient civilisations. Rather than working toward a bold vision for the common good, they concentrated on personal enrichment, waged wars, erected grand monuments, and exploited the peasantry to finance their endeavours.

The MWP was succeeded by a prolonged period of cold, termed the Little Ice Age (LIA), which persisted until the mid-nineteenth century and was characterised by agricultural crises and the proliferation of devastating infectious diseases such as plague and famine throughout Europe. The severity of the LIA fluctuated across different regions. For example, Asia experienced economic turmoil in the 17^th century, with China’s Ming Empire enduring severe droughts. Thousands perished from hunger in Japan and Korea during the 1640s.

Tree ring analysis has uncovered significant variations in monsoon precipitation in Southeast Asia from 1450 to 1820. These climatic changes impacted numerous medieval cities in South Asia, with Angkor in Cambodia serving as a notable illustration. The tree-ring studies reveal a significant drought affecting Angkor around the mid-14^th century, followed by intense monsoons and another drought. What we observe here is not a societal collapse but instead urban resilience. The climatic challenges forced their society to evolve from an agrarian kingdom into smaller trading cities along the Mekong Delta. A substantial increase in the frequency of drop in agricultural production famines in the late seventeenth century in north India was recorded during the Mughal period due to abnormal weather patterns. It compelled the rulers to introduce water management systems like canals and reservoirs to lessen the impact of droughts and floods.

Ignoring the lessons of the past – hundreds of thousands of years of adaptation to climate change – may well prove to be short-sighted. The climatic challenges faced by the Mayans, the Harappans, medieval European farmers, and the Mughals of India may not be directly comparable to the current global warming in terms of its temporal or spatial scale. However, understanding how some societies adapted and survived, while others failed is crucial for planning effective adaptation strategies.

What earlier generations lacked were the benefits of modern science that assist in climate forecasting. As climate historians Brian Fagan and Nadia Durrani remind us, we must maximise enduring qualities such as forward-thinking, planning, intellectual reasoning, and innovation. Another significant lesson from the past pertains to leadership. The current climate change represents a global phenomenon that requires leaders who can foster cooperation among countries rather than pursue dominance over others due to a misguided sense of entitlement. This reflects a profound detachment from reality, as we must remember that the future of all humanity is at stake – either we sink or swim together.

(Published under Creative Commons from Mongabay-India. Read the original article here)