Those who deny climate change caused by mankind tend to cite the so-called “Little Ice Age” as one of their arguments to defend the hypothesis of the natural origin of climate changes. The Little Ice Age, as it is known, to distinguish it from the great ice ages, covers a period from 1350 to 1850 approximately, when there was a significant lowering of the global average temperature with respect to the five previous centuries. The planet was emerging from a period known as the “Medieval Climate Optimum” and both processes have led the so-called “sceptics” or “deniers” to deduce from this, among other factors, the natural origin of present climate change. The warming that we are witnessing today, they deduce, comes from a new cycle of solar activity and not from human activity.

Up to now, the hypotheses to explain the Little Ice Age pointed to a reduction of solar activity and an increase in volcanic eruptions, which provoked ash clouds that limited the entry of the radiation of the sun. Nevertheless, a few days ago, an investigation was published by the University College of London[1] that explains that the Little Ice Age was also the result of human activity. And one more ruthless than the combustion of fossils or deforestation.

Alexader Koch, the main author of the study, is in reality more preoccupied by the definition of the beginning of the Anthropocene, the name that the scientific community has proposed as the successor of the Holocene (the present epoch of the Quaternary period in terrestrial history) due to the significant global impact that human activities have had on terrestrial ecosystems. Koch had been involved in research that linked a reduction of atmospheric carbon dioxide in past centuries to the increase of carbon sequestration in the earth. If the colonization of America were responsible for this process, as others have suggested, then this event would be a good candidate to establish the beginning of the Anthropocene.

The authors found in their process of investigation that it was the “Great Dying of the Indigenous Peoples of the Americas” that contributed significantly to the cooling of the planet in this period. There were previous hypotheses with similar content, that associated the influence of the Black Death and the consequent depopulation of Eurasia with this phenomenon and the researchers of the College wondered what influence the depopulation in America could also have had.

The arrival of Cristopher Columbus in the Bahamas in 1492 marks the beginnings of one of the greatest genocides in history. To the deaths by the sword, blunderbuss and torture, are added the epidemics and illnesses that caused the extermination of the majority of the indigenous population and consequently of those who would have lived during the following century.

Land use by the indigenous had been generalized before the arrival of the Europeans, especially in Mexico, Central America, Bolivia and the Andes, where they practiced terraces and irrigation agriculture, and in almost all of the Amazon region, where diverse pre-Columbian uses of the land left their traces in the composition of the forests of the Amazon. Hence, the extermination of the American indigenous peoples led to a reduction of agricultural usage of the land. The fields and areas left fallow produced a revegetation that increased the carbon reserves to return to similar previous states. In fact the reforestation of degraded lands is today one of the measures undertaken in the whole world to revert global warming.

The capture of carbon in the lands abandoned after the European conquest could have been sufficient to reduce the atmospheric content of CO2. The registered amounts of the ice nucleus in the Antarctic and of the concentration of CO2 in the atmosphere reflect an abnormally large reduction of 7-10 ppm (parts per million) as from the decade of 1500. The analysis of data received indicates that this anomaly is due to an increase in the amounts of terrestrial carbon sinks. Hence, the capture of carbon that is believed to have been produced following the arrival of the Spanish in the Americas could have reduced the levels of CO2 in the atmosphere and contributed to the Small Ice Age.

The reduction of the global atmospheric concentration of CO2 at the end of the 16th and beginnings of the 17th Century reduced the global temperature of the air on the surface by 0.15º C. So the scientists who took part in this investigation wanted to verify if this change of temperature had been due to natural causes or the result of the depopulation on a large scale produced in America.

According to the study, 55 million indigenous died during the first years of the Spanish conquest after 1492. This led to the abandonment of some 56 million hectares of land in which there was a regeneration of vegetation that absorbed 7.4 GtC (gigatonnes of carbon) eliminating them from the atmosphere. Considering feedback processes, the investigators concluded that this contributed to between 47% and 67% of the reduction of atmospheric CO2 between 1520 and 1610. As we have indicated, this reduction has been estimated at between 7 and 10 ppm of CO2, according to the records carried out on the basis of the nucleus of Antarctic ice and corresponds to a value of between 15 and 22 GtC in the atmosphere.

These changes, according to the study, indicate that the Great Dying of Indigenous Peoples of the Americas (as the authors call the genocide) must be considered a fundamental element for a complete explanation of the anomalous reduction of atmospheric CO2 at that time and the resulting lowering of global temperatures of the surface air.

Without a doubt, this is not the greatest impact that resulted from the arrival of Europeans to the Americas, nor is it the worst of the consequences of the devastating period of the conquest. But this investigation tells us that human actions also had a global impact on climate change long before the Industrial Revolution. The massacre of the American indigenous peoples had a detectable impact over both atmospheric CO2 and global temperatures, two centuries before the first steam engine in the English mines.

29/04/2019

(Translated for ALAI by Jordan Bishop)

- Gerardo Honty is a researcher with CLAES (Centro Latino Americano de Ecología Social).