Agricultural land was expanded through deforestation. The increase in agricultural land at the expense of forested land slightly altered rainfall, slightly increasing the severity of naturally occurring droughts. This increased the likelihood of famine and disease, amplifying the other factors that lead to the collapse of the Classic Mayan culture.
This potential demonstration of historical human influence on climate supports the concept that we have left the Holocene and entered the Anthropocene. It is also one more demonstration that the concept of “Rain follows the plow,” which was influential in expanding settlement of the American West & Great Plains in the 1800s, was flawed.
There are still many non-scientists who state that any claims of human caused changes in climate are simply ‘hubris’, but the growing list of examples of relatively small populations altering regional climates in the past should convince them of the plausibility of seven billion people altering the global climate.