Ice sheets in Greenland 3000 years ago were even smaller than today

Greenland's shrunken ice sheet is nothing new, scientists say -- it was even smaller more than 3,000 years ago, as small as any time in recent history. A new technique for interpreting the Arctic fossil record has allowed a determination of when glaciers were smaller than they are today, the researchers said. While there are techniques for figuring out when ice sheets were larger, finding just the opposite has been difficult, they said. "Traditional approaches have a difficult time identifying when ice sheets were smaller," said study leader Jason Briner, a geology professor at the State University of New York at Buffalo. "The outcome of our work is that we now have a tool that allows us to see how the ice sheet responded to past times that were as warm or warmer than present -- times analogous to today and the near future." The technique the scientists developed involves dating fossils found at the edge of glaciers, left in heaps of rubble called moraines as glaciers advance and retreat. "What's really interesting about this is that on land, the atmosphere was warmest between 9,000 and 5,000 years ago, maybe as late as 4,000 years ago," Briner said. "The oceans, on the other hand, were warmest between [5,000 and 3,000] years ago," when the ice sheet was at its smallest, he said. "What it tells us is that the ice sheets might really respond to ocean temperatures," he said. "It's a clue to what might happen in the future as the Earth continues to warm."