Almost 6 years ago, a paper in Science warned of an unheralded environmental peril. Melted snow and ice seemed to be reaching the base of the great Greenland ice sheet, lubricating it and accelerating the sheet's slide toward oblivion in the sea, where it was raising sea level worldwide (12 July 2002, p. 218). Now a two-pronged study-both broader and more focused than the one that sounded the alarm-has confirmed that meltwater reaches the ice sheet's base and does indeed speed the ice's seaward flow. The good news is that the process is more leisurely than many climate scientists had feared.

When people talk about catastrophic climate change, there's a fair chance that Greenland is on their mind. If they use the term 'tipping point', then it is pretty much a sure thing. One-twentieth of the world's ice is locked up atop that island, and if it were to melt completely, global sea levels would rise by seven metres. The collapse of the Greenland ice sheet is in the front rank of potential climate catastrophes.

Attaching a 'floating' tree-ring chronology to ice core records that cover the abrupt Younger Dryas cold interval during the last glacial termination provides a better estimate of the onset and duration of the radiocarbon anomaly. The chronology suggests that marine records may be biased by changes in the concentration of radiocarbon in the ocean, which may affect the accuracy of a popular radiocarbon calibration program during this interval.

Because of difficulties in creating a radiocarbon calibration that covers the end of the last glaciation, defining the timing and duration of the Younger Dryas cold event has been a challenge. Linking related cosmogenic isotopes in tree rings and ice cores may provide new insights into abrupt climate changes.

It is difficult to obtain fossil data from the 10% of Earth's terrestrial surface that is covered by thick glaciers and ice sheets, and hence, knowledge of the paleoenvironments of these regions has remained limited. We show that DNA and amino acids from buried organisms can be recovered from the basal sections of deep ice cores, enabling reconstructions of past flora and fauna.