Holocene Southwest Greenland Ice-Sheet Retreat Suggests Recent Ice Retreat Is A Response To Global Warming

We use 10-Be surface exposure ages from boulders in southwest Greenland to date when the Greenland Ice-Sheet margin was inland of its late-Holocene maximum extent. In south Greenland, ice retreated within its late-Holocene extent at 11.3±0.2 to 10.8±0.3 ka. Southwest and west Greenland Ice-Sheet margins were inland of their present extent at 7.1±0.2 and 7.9±0.1 ka, respectively. Fully-coupled climate model simulations from 9 ka to 2100 C.E. show that the modeled modern ice-melt anomaly caused by anthropogenic greenhouse gas emissions already equals that which drove the southwest Greenland Ice Sheet to a reduced extent in the early Holocene from changing orbital forcing. Thus, assertions that anthropogenic greenhouse gases forced recent southwest Greenland Ice-Sheet retreat are consistent with the geologic record of this ice sheet's response to past forcings of a comparable magnitude.