SciencePrehistoric (Cretaceous-Paleogene boundary, ~66 million years ago)globalhigh confidence

During the global winter caused by the asteroid impact, temperatures fell below freezing.

Notes on verification

Corroborated by multiple peer-reviewed studies (PNAS, GRL, Nature Geoscience) and institutional summaries (LPI/USRA, AGU) consistently reporting sub-freezing global temperatures following the Chicxulub impact.

Sources