Analyses of sediments retrieved from a drifting ice island suggest that the Arctic Ocean may have been ice free and as warm as 15℃ about 70 million years ago. Therein is a challenge for climate models. Various lines of evidence show that Earth's climate was much warmer during the Cretaceous period than it is today. Yet that evidence — fossil plants and animals, sedimentary features and geochem-ical indicators — is sparse, spotty and often inexact, making the magnitude and distribution of Cretaceous temperatures highly uncertain. In a testament to quality over quantity, Jenkyns et al. (page 888 of this issue) have produced a single new datum from one of the coldest spots on Earth's surface: their work clarifies the nature of extreme warmth in the Cretaceous, and reveals that the past was radically different from the present.
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