When will the summer Arctic be nearly sea ice free? In a recent article, Overland and Wang address this question and attempt to predict 21st century summer Arctic sea ice loss by applying three distinct approaches to the problem. The first is related to sea ice volume loss, which is a better variable than sea ice extent, because ice volume is decreasing at a percentage rate higher that sea ice extent. Analysis of modeling and observations depicted a negative trend in sea ice volumes after 1995 and projections show a nearly sea ice-free summer before 2020. The second of these approaches is related to natural variability, which drive changes in sea ice sensitivity with respect to large meteorological or oceanic events, produces a wide distribution of possible trends in sea ice extent, and can cause rapid ice loss events. Consideration of natural variability suggests that it will take several rapid loss events to reach a sea ice extent threshold that drives the arctic to ice free conditions. Modeling shows a nearly sea ice-free summer in the Arctic by 2030 ±10 years. The third approach is related to Global Climate Models (GCMs). GCMs provide future projections of the state of the atmosphere, ocean, land and sea ice, under different environmental conditions. Results from these models are available to the scientific community through Coupled Model Intercomparison Project phase 5 (CMIP5). More than 20 models show loss of sea ice as greenhouse gas concentrations increase. However, model hindcasts results are variable and 80% of ensemble members have trends that are of less magnitude than observations. Under high greenhouse gas emission the average of all models do not reach ice-free conditions by 2100. This study highlights that at present it is not possible to choose one approach over another. However, they all predict an eventual sea-ice free Arctic based on increases in greenhouse gas forcing, and therefore “society should start managing for the reality of climate change in the Arctic”.
Overland, J.E. and M. Wang. 2013. When will the summer Arctic be nearly sea ice free?. Geophysical Research Letters 40: 2097-2101, doi:10.1002/grl.50316