Between 750 and 900 CE, the population of the Maya lowlands declined sharply, and repeated droughts have long been the favoured culprit. A study in Biogeosciences led by Benjamin Gwinneth, professor of geography at Université de Montréal, complicates that tidy narrative. His team extracted sediment cores spanning roughly 3,300 years from Laguna Itzan, a lake beside a Maya archaeological site in northern Guatemala, and read them with three geochemical indicators.
Polycyclic aromatic hydrocarbons traced the intensity of slash-and-burn fires, leaf waxes recorded vegetation and rainfall, and fecal stanols estimated population density. The record shows human activity from about 4,000 years ago and permanent settlement from about 3,200 years ago, with heavy fire use in the Preclassic giving way, during the Classic period, to substantial population growth alongside declining burning, evidence of more intensive, erosion-conscious agriculture serving a growing urban centre.
The crucial finding is what the sediments do not show: hydrogen isotope analysis revealed no evidence of local drought, which the authors attribute to orographic rainfall where Caribbean air meets the nearby mountains. Yet Itzan's population still collapsed in the Terminal Classic and the site was abandoned. Gwinneth argues that drought in the central lowlands triggered cascading crises, wars, dynastic collapse, migration and broken trade routes, that pulled even well-watered cities down, a sobering lesson about interconnected societies facing environmental stress.