What was done
Based on radiocarbon dating and pollen analyses of a sediment core retrieved from the shore of Naja Lake (16°59'27.6"N, 91°35'29.6"W), which is located near the Lacandon Forest Region in the state of Chiapas in southeastern Mexico -- which the authors say "has been inhabited by the Maya since the early Formative Period (ca. 1,000 BC)" -- they derived a 2000-year history of regional drought.

What was learned
Dominguez-Vazquez and Islebe report that "a marked increase in Pinus pollen, together with a reduction in lower montane rain forest taxa, is interpreted as evidence for a strong, protracted drought from 1260 to 730 years BP," which they characterize as "the most severe" of the record. In fact, they write that "the drought coincides with the Maya classic collapse and represents the most pronounced dry period of the last 2,000 years in the Lacandon area."

What it means
As much as the higher temperatures of the Medieval Warm Period that were experienced in Greenland benefited the Vikings who contemporaneously colonized that part of the world, its greater dryness in southeastern Mexico cursed the indigenous Maya who had called that region home for close to 2,000 years, indicative of the fact that millennial-scale climate change may both help and harm human societies at one and the same time, depending upon their unique circumstances. It is also equally clear that these changes of the past occurred independently of any changes in the air's CO2 content, and that if the world is in the initial stages of a "repeat performance" of the warming phase of this cycle, both positive and negative impacts can be expected once again. Consequently, the world should be preparing to capitalize upon the positives of the phenomenon and cope with its negatives, rather than trying to restrict anthropogenic CO2 emissions that likely have little or no impact on what has been a natural recurrent feature of the planet's climate throughout both glacial and interglacial periods alike.