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The late 15th century ushered in a dramatic chapter in world history with the arrival of Europeans in the Americas. This moment of contact between continents marked the beginning of profound and far-reaching transformations. But while it is often remembered for its historical, cultural, and political implications, this era also coincided with an enigmatic and significant climatic shift: a cooling of the Earth’s atmosphere.

Known as the Little Ice Age, this period of global cooling remains a subject of curiosity and study among historians, scientists, and environmental researchers. And what makes this cooling event particularly intriguing is its apparent connection to the colonization of the Americas.

How could human actions during such a devastating period in history have contributed to a global phenomenon that shaped weather patterns, agriculture, and ecosystems for centuries? Click through to find out.

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The arrival of Europeans in the Americas at the end of the 15th century was fueled by the quest for wealth, new trade routes, and territorial expansion. Led by explorers like Christopher Columbus, these voyages connected two worlds, and ultimately reshaped global history.

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As nation-states like Spain and Portugal consolidated their power, they vied for dominance in exploration and colonization. This rivalry pushed them to claim new territories and establish trade networks to outcompete their neighbors.

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Europeans introduced new plants, animals, and technologies to the Americas, while bringing back crops like maize, potatoes, and tomatoes to Europe. This exchange reshaped diets, economies, and ecosystems on both sides of the Atlantic.

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The arrival of Europeans also introduced diseases such as smallpox, measles, and influenza to the Americas, to which Indigenous populations had no immunity. These diseases decimated Indigenous communities, with mortality rates reaching catastrophic levels.

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As devastating diseases swept through vast areas of Indigenous populations, up to 55 million people died, which accounted for 90% of native communities. But diseases were not the only factor that led to the massive loss of life.

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European colonization was often accompanied by wars, massacres, and violent displacement of Indigenous communities. Military conquests typically involved large-scale killings and destruction of native societies for the purposes of claiming land and resources.

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As Indigenous populations plummeted, native agricultural lands spanning millions of acres were deserted. These vast areas, once cleared and farmed, were reclaimed by fast-growing trees and a plethora of other vegetation.

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As vast expanses of abandoned farmland were naturally reforested, growing trees and plants became efficient at absorbing carbon dioxide. This massive carbon capture led to measurable reductions in how much CO₂ was present in the atmosphere.

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Carbon dioxide (CO₂) is a greenhouse gas that traps heat in the Earth’s atmosphere. When sunlight reaches the Earth, it is absorbed and reemitted as infrared radiation. CO₂ absorbs this radiation, preventing it from escaping into space, which in turn warms the planet.

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Increased CO₂ levels enhance this greenhouse effect, leading to higher global temperatures and altering climate patterns. During the medieval era (before the industrial age and the rise of pollutants), CO₂ came from more natural processes, such as volcanic activity, wildfires, and decomposition.

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Abandoned lands during the colonization of the Americas triggered a cascade of ecological rewilding. Experts believe that approximately 56 million hectares of land fell into disuse, which is close in size to some countries like France.

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Expanding forests supported diverse plant life and regenerated ecosystems. This extensive regrowth is estimated to have absorbed enough CO₂ to reduce its concentration in the atmosphere by 7–10ppm (parts per million), meaning 7–10 fewer CO₂ molecules for every million molecules of air.

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To put this in a modern context, humanity currently emits around 3ppm of CO₂ into the atmosphere every year through the burning of fossil fuels. The colonization of the Americas essentially stripped the globe of three times the amount of CO₂.

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The regrowth of dense forests also altered surface albedo, or reflectivity. Dark, leafy canopies absorbed more sunlight than croplands, helping trap less heat in the atmosphere. This interaction played a role in intensifying the cooling already underway.

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As temperatures around the world dropped, it contributed heavily to the Little Ice Age, a period of cooler temperatures from the 14th to 19th centuries. Reduced human impact in the Americas intensified this cooling trend and intertwined natural climate cycles with shifts in land use.

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Cooler temperatures during the Little Ice Age shortened growing seasons and led to poor harvests. Crop failures were widespread, resulting in famines and economic instability, particularly in Europe and parts of Asia, where food security was already fragile.

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Regions experienced unusually cold winters during the Little Ice Age, with rivers like the Thames in England and canals in the Netherlands freezing over. Shifting weather patterns brought storms, floods, and erratic rainfall that exacerbated the challenges of life during this period.

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Scientists have analyzed ice sheets in Antarctica to further understand the devastating impact that colonization had in the 15th century. Air bubbles trapped in frozen ice samples dating to this period show that there was a fall in concentration of carbon dioxide during this era.

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After analyzing ice sheets, scientists observed that 7.4 petagrams—equivalent to seven billion metric tonnes—of carbon had abruptly vanished from the atmosphere between 1520 and 1610. This coincided closely with the mass deaths of Indigenous populations in the Americas.

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The global drop in temperatures was compounded even more over time. As snow fell on the ground, more of the sun’s warming rays were reflected back into space, which cooled the planet further. Ultimately, the stretch of cold only began to decline during the first Industrial Revolution, almost 200 years later.

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Before colonization, Indigenous practices maintained ecological balance, preventing massive carbon sequestration events. But this was not the last time that colonial powers in the Americas created a climate imbalance across the globe.

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In the 19th century, tens of millions of bison were slaughtered across the Great Plains of North America. This mass extermination, driven by overhunting and government policies, nearly wiped out the species by the late 1800s.

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Bison were keystone species that played a crucial role in maintaining grassland ecosystems. At the start of the 19th century, there were between 30 and 60 million bison on the continent, but their population was ultimately reduced to only 456. This picture of bison skulls was taken in 1892.

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The extermination of millions of bison played a major role in temperature and climate changes. The grazing patterns of bison encouraged healthy plant growth, which helped sequester carbon in the soil. The loss of bison disrupted this balance, reducing the carbon-capturing capacity of the plains.

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Without the trampling and grazing of bison, grasslands became less stable, leading to increased soil erosion. This exposed carbon-rich soil to the atmosphere, causing the release of stored carbon and contributing to localized climate effects.

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After the bison were removed, cattle replaced them as the dominant grazing animal. Unlike bison, however, cattle grazing often degraded the land further, especially when managed unsustainably, resulting in overgrazing, loss of plant cover, and additional soil carbon loss.

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Bison and cattle both produce methane, but the replacement of wild herds with managed livestock may have altered the balance of methane in the atmosphere. While bison populations had fluctuated naturally, their sudden mass extermination meant that the greenhouse effect was drastically reduced.

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The mass killing of bison not only devastated Indigenous cultures that depended on them, but also had long-term environmental consequences. The collapse of grassland ecosystems disrupted carbon and nitrogen cycles, impacting the climate and reducing the resilience of the plains.

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These historical events brought to light the profound (and sometimes unintended) impact that humanity has on the planet. They should serve as a cautionary tale, emphasizing the need to balance human activity with the preservation of ecosystems to safeguard the planet’s delicate equilibrium.

Sources: (BBC) (University College London) (Global News) (Britannica) (The Conversation)