The massive Mount Toba eruption around 74,000 years ago appears to have had far less climate impact than previously thought, according to new research published in *Ars Technica*. Scientists once believed the eruption—Earth's largest in the past 2.6 million years—might have triggered a volcanic winter severe enough to nearly wipe out early humans. However, a team led by geoscientist Jinheum Park from Johannes Gutenberg University analyzed sediment layers from Lake Chala in Tanzania, a crater lake with annual varves that act like tree rings.

The researchers found that the eruption's effects lasted less than two years and resulted in only about half a degree of cooling. While earlier computer models produced wildly varying results due to uncertain estimates of sulfur emissions, the lake's precise sediment record revealed a clear, short-lived impact. The ash layer, barely visible and just 0.3 millimeters thick, was followed by two thin green films interpreted as diatom stress responses, then a pronounced bloom in the next dry season.

By the third year, climate conditions had returned to normal. The team used silicon-to-aluminum and manganese-to-iron ratios to estimate the cooling at roughly 0.5 degrees Celsius, far below the threshold needed to disrupt the lake's regular layering. The sediment core also pinned the eruption to January or February, contradicting earlier seasonal estimates. These findings suggest that while Toba was colossal, it posed little threat to human survival.