A history lesson from Greenland's melting ice
Having a tough time figuring out how quickly Greenland鈥檚 ice cap could melt? Look to the past for clues. That鈥檚 what an international team of scientists led by Anders Carlson of the University of Wisconsin has done. Based on its analysis, the team says, history teaches that under the right conditions, the ice can disappear relatively rapidly.
They turned to the Laurentide Ice Sheet for their history lesson. At the height of the last ice age, some 20,000 years ago, it covered much of North America and came as far south as New York and Ohio. During its long thaw, however, it went through two accelerated melt-offs. One started 9,000 years ago and lasted 500 years. The second began 7,600 years ago and lasted 800 years. Geological and marine evidence, along with modeling results, for these events pointed to a rate of sea-level rise of 4.2 feet per century for the earlier period, and 2.2 feet per century for the second period.
The drivers then were changes in sunlight hitting the region as Earth鈥檚 orbit around the sun underwent one of its periodic shifts in shape, the team notes. And Earth鈥檚 tilt was shifting. But, they add, the warming that the remaining ice sheet underwent in summer during these periods of accelerated melting is within the range of warming one might expect to see by century鈥檚 end if carbon dioxide concentrations in the atmosphere reach twice their pre-industrial levels.
Measurements of Greenland鈥檚 mass balance aren鈥檛 long enough 鈥� and computer simulations of ice-sheet movements aren鈥檛 advanced enough 鈥� to help explain with much confidence the changes scientists are seeing in Greeland鈥檚 ice today. So this latest work is more suggestive than conclusive, the team acknowledges. Still, the work implies that 鈥渇uture reductions of the Greenland ice sheet on the order of one meter per century are not out of the question,鈥� note Mark Siddall and Michael Kaplan 鈥� researchers not directly involved in the study 鈥� in a commentary accompanying the work.
Both appear in the current edition of Nature Geoscience.
