How fast will our coastlines be swallowed up by rising sea levels? This week, an ice-age glacier lent support to the controversial view that sea levels could rise by 1 metre per century - and so drown land now occupied by 145 million people by 2100. To get a better idea, Anders Carlson of the University of Wisconsin-Madison and colleagues looked at what had happened at the end of the last ice age, when the last fragments of the Laurentide ice sheet covered much of north-eastern Canada. The team studied beryllium isotope ratios in the ancient bedrock to determine the ice sheet's margins between 9000 and 6800 years ago - these ratios alter depending how much of the bedrock was exposed. They worked out that melting ice must have raised sea levels by 0.7 to 1.3 metres per century. Using one of the IPCC's latest climate models, they calculated the temperature change that led to these rises, and compared it to changes expected over Greenland by 2100 (Nature Geoscience, DOI: 10.1038/ngeo285).