The Mongol Empire, spanning the 13th and 14th centuries, stands as a monumental force in human history. It was the largest land empire ever known, stretching from the Sea of Japan deep into Eastern Europe, and encompassing vast territories across Asia, the Middle East, and Russia. Its legacy is predominantly associated with unparalleled military conquests, rapid expansion, and profound geopolitical transformation. However, beyond the well-known stories of war and social change, there is a lesser-known chapter: the empire’s complex yet significant role in capturing and storing carbon. This unexpected environmental footprint, driven by both unplanned consequences and later, more deliberate policies, offers a fascinating historical parallel to modern sustainability efforts. It compels a deeper examination of the often unforeseen connections between human civilisation and the planet’s ecological health.

 The conditions that facilitated the Mongol Empire’s rise were, in part, shaped by a period of unusually favourable climate. Tree-ring studies, conducted by paleoclimatologists such as Neil Pederson and Amy Hessl, have unveiled that the years between 1211 and 1225, a period precisely coinciding with Genghis Khan’s ascendance, saw Central Asia experience its mildest and wettest weather in over a millennium. This “unusual moisture” dramatically boosted plant productivity on the normally arid steppes, leading to an abundance of lush grasslands. This verdant landscape provided ample forage for the immense numbers of war horses and other livestock that formed the logistical backbone of the Mongol military, enabling their rapid and extensive conquests. Genghis Khan literally “rode the wave” of climatic advantage, transforming environmental conditions into a strategic asset that fueled his empire’s expansion. 

 The Mongol armies’ invasions resulted in widespread depopulation across vast cultivated lands. Historical estimates suggest that the Mongol army slaughtered approximately 30% of the 115 million people they encountered during their advance. With fewer people to farm, large tracts of agricultural land were abandoned and gradually returned to natural forests and other vegetation. This large-scale reforestation acted as a significant carbon sink, absorbing atmospheric carbon dioxide. Research by Julia Pongratz of the Carnegie Institution’s Department of Global Ecology found that this regrowth sequestered an estimated 700 million tonnes of carbon from the atmosphere. To put this into perspective, this astonishing amount is equivalent to the quantity of carbon produced in a single year from today’s global gasoline demand. Pongratz’s research further highlights that the prolonged nature of the Mongol invasions and the subsequent longevity of their empire, which lasted for two centuries, were crucial for this environmental effect to materialise fully. This extended period allowed sufficient time for forests to regrow and absorb significant amounts of carbon. This phenomenon has led some ecologists to label Genghis Khan an “unintentional eco-warrior” or even the “greenest invader” in history.

 The Mongol Empire’s environmental engagement evolved beyond the accidental reforestation spurred by its initial conquests. Later rulers, particularly Kublai Khan, demonstrated a more deliberate and policy-driven approach to environmental management within the empire’s vast territories, especially in settled agricultural regions. Recognising the critical importance of agricultural stability and efficient resource management for governing a vast empire, Kublai Khan established an “Office for Stimulation of Agriculture”.

 This office spearheaded specific policies aimed at fostering environmental well-being. Communities were encouraged to undertake “self-help projects” that included planting trees, developing irrigation systems, implementing flood control measures, stocking rivers and lakes with fish, and promoting silk production. These initiatives were not abstract environmental goals but rather practical efforts designed to ensure food security, prevent famine, and enhance economic prosperity across the empire. Furthermore, the empire demonstrated a commitment to facilitating trade and travel along the extensive Silk Road network by planting “trees along the roads to shade the merchants and travellers in the summer months”. This illustrates a deliberate effort to improve infrastructure while also caring for the environment — a lesson current projects can borrow from. 

  In modern Mongolia,  efforts have been made in large-scale reforestation. The nation has launched an ambitious “One Billion Trees” national campaign, initiated in 2021 by President Khurelsukh Ukhnaa, with the explicit goal of planting one billion trees by 2030. This initiative directly addresses pressing environmental challenges, particularly desertification, which severely impacts 76.9% of Mongolia’s territory. The campaign aims to increase forest coverage to 9%, enhance greenhouse gas absorption, and increase vital water resources.  

 The environmental legacy of the Mongol Empire is a multifaceted narrative, encompassing both unintentional and intentional aspects. The initial conquests, through widespread depopulation, inadvertently facilitated massive carbon sequestration as cultivated lands returned to forests. This was later complemented by more deliberate tree-planting and agricultural management efforts under rulers like Kublai Khan, driven by pragmatic needs for stability and prosperity.

The Mongol Empire’s story serves as a compelling reminder that human actions, even those not explicitly aimed at environmental outcomes, can have far-reaching and lasting impacts on the planet’s climate. The “green legacy” of the Mongols, however unintended or pragmatically driven, highlights the profound and often underestimated power of nature-based solutions, such as reforestation and ecological restoration. These approaches remain critical tools for climate resilience and carbon sequestration in the contemporary fight against climate change, offering valuable insights from centuries past that can inform our future health and well-being.