The rise in maximum summer temperatures in the Mayan states coincided with an increase in the number of records of wars between countries.
A group of American researchers decided to find out how intense warming affects the frequency of military conflicts between states. Intense warming in 363–888 AD led to an increase in summer temperatures in the areas of the Mayan states. Despite the warming, the amount of precipitation did not decrease during that period. At the same time, the frequency of references to military conflicts in written sources has increased dramatically during this time. Scientists note the possibility of the development of similar processes during the current warming. A related article was published in Quaternary Science Reviews.
The authors of the work compared the number of commemorative signs and stelae with the records of the conduct of war by this or that ruler, left by the Maya in 363-888 AD, with the temperature and precipitation in the same period in the same region. Temperature and precipitation data were obtained from the analysis of precipitation at the bottom of local lakes. The deposition rate of such precipitation depends on both temperature and rainfall intensity.
It turned out that the amount of precipitation changed little during this period, starting to decrease only at the very end. At the same time, the number of records of the conduct of wars also decreased. However, this does not mean that there is a relationship between the frequency of wars and the amount of precipitation. The fact is that by the year 900, simultaneously with the fall in precipitation intensity, the classical Mayan states basically ceased to exist, and the urban culture in this area was revived only after a hundred years. So the researchers state that the connection between precipitation and the frequency of wars between the Mayan city-states has not been established.
However, a correlation was found between the maximum summer temperatures in this region and the frequency of armed conflicts. In the years 363–888, summer temperatures rose here, and in parallel the number of wars mentioned in the records increased. The authors attribute this to the fact that at daytime temperatures above 30 degrees Celsius, the corn of the typical Mayan varieties grew more slowly than normal. In theory, this could cause food shortages and provoke wars with neighbors for better lands.
It should be noted that it is extremely risky to draw direct parallels between warming and the increase in the intensity of wars. During the cold snap in Europe in the 15th-17th centuries, wars became more frequent and began to bring more losses without any warming - mainly due to religious schism in European states. In the first half of the 20th century, wars returned to a huge (as a percentage of the population) level of losses in the 17th century, although there was no active warming or an active cooling at that time.
In modern historiography, it is generally accepted that a rather complex society generates conflicts more or less often, mainly depending on the internal socio-economic or cultural processes going on in it. Nevertheless, the logic of the authors of the work under discussion is different. If historians of Western societies used it, they could conclude both that cold snaps caused wars in Europe, and that they were stimulated simply by a stable climate.