Mesoamerican rainfall anomalies, AD 800--950; source NASA GISS

There is increasing evidence that not only are we currently altering the global climate, but that humans have influenced regional climates in the past. A good place to start looking at this idea is today’s post on the NASA Earth Observatory. The paper discussed contributes to the evidence that Mayan agriculture contributed to the collapse of Mayan society in the AD 800s. My interpretation of the current best understanding can be summarized as:

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.