While Europe was in the early days of the Renaissance, there were empires in America that held more than 60 million people. But the first European contact in 1492 brought the disease to the Americas that devastated the domestic population, and the collapse of agriculture in the Americas was so significant that it might even cool the global climate.
The number of people living in North, Central and South America when Kolumbo came to the question is what researchers are trying to answer for decades. Unlike Europe and China, no records of the size of indigenous societies in America were preserved before 1492. In order to reconstruct the population, the researchers rely on the first statements of European eyewitnesses and, according to colonial rule, tax payments known as "encomiendas". This taxation system has only been established after the European epidemic has ravaged America, so there is nothing to tell us about the size of pre-colonial populations.
Early reports of European colonists were likely to overestimate the size of the settlement and the population in order to rekindle the wealth of their newly-discovered countries with their feudal sponsors in Europe. But by rejecting these allegations and focusing on colonial records, at the beginning of the 20th century, extremely low population estimates were made that counted the population after the disease was destroyed.
On the other hand, liberal assumptions about, for example, the share of indigenous peoples who had to pay the tribute or the rate at which people died had led to extremely high estimates.
Our new study clarifies the size of pre-Columbian populations and their impact on the environment. By combining all published estimates from populations across America, we find a likely indigenous population of 60m 1492. By comparison, the European population at that time was 70-88m distributed in less than half of the area.
The great pre-Columbian population was maintained through agriculture – there are extensive archaeological evidence for grazing and burning farming, terrain fields, large earthquakes and homes.
Knowing how much agricultural land is needed to maintain a person, the number of inhabitants can be translated from areas known to be used for human land. We found that 62 million hectares of land, or about 10% of land masses in America, were bred or under other human use when Kolumbo arrived. By comparison, in Europe, 23%, and in China, 20% of people used humans at that time.
This changed in decades after Europeans first crossed the island of Hispaniola in 1497 – now Haiti and the Dominican Republic – and the mainland in 1517. Europeans brought measles, big pussycats, flu and bubonic plague across the Atlantic, with devastating consequences for indigenous peoples.
Our latest best estimate is 56 million deaths in the early 1600s – 90% of pre-Columbian indigenous population and about 10% of the world's population at that time. Because of this, "Great Death" is the largest event of human mortality proportional to the global population, placing it second in absolute terms only for the Second World War, where 80 million people died – 3% of the world's population at that time.
The 90% mortality rate in America after the contact is remarkable and surpasses similar epidemics, including the Black Death in Europe – resulting in a 30% loss in Europe. One explanation is that multiple waves of epidemics hit the indigenous immune system that evolved in isolation from the Euro-Asian and African populations 13,000 years ago.
Indians at that time had never been in contact with pathogens brought by colonists, creating a so-called "virgin soil" epidemic. People who did not die of the big goddess died from the next wave of flu. Those who have survived have been subjected to measles. War, hunger and colonial atrocities have made the remnant in the Great Death.
This human tragedy meant that there were not enough workers to manage fields and forests. Without human intervention, the pre-managed landscapes returned to their natural state and absorbed carbon from the atmosphere. The extent of this growth of natural habitat was so great that it removed enough CO₂ to cool the planet.
Lower temperatures triggered feedback in the carbon cycle that eliminated even more CO₂ from the atmosphere – such as releasing CO₂ from the ground. This explains the fall of CO₂ at 1610 on the Antarctic ice cores, solving the riddle of why the whole planet was short in the 17th century. In that period, severe winters and cold summers cause hunger and rebellion from Europe to Japan.
The modern world began with a disaster of almost unimaginable proportions. Yet America is for the first time associated with the rest of the world, marking the beginning of the new era.
Now we know more about the proportions of the pre-European American population and the Great Death that erased them. Human activity at that time caused a fall in atmospheric CO₂ that cooled the planet long before human civilization dealt with the idea of climate change.
However, such a dramatic event would not have contributed much to mitigating the speed of modern global warming. The recent afforestation event in North and South America has led to a reduction of 5 parts per million CO₂ from the atmosphere – just about three years of fossil fuel emissions today.