Arctic sea ice decline and ice export in the CMIP5 historical simulations

Speaker: 
Florian Geyer
Affiliation: 
Nansen Environmental and Remote Sensing Center
Seminar Date: 
31. May 2012 - 12:30 - 13:00
Location: 
Lecture room, Ground Floor, NERSC

Arctic sea ice properties of the historical simulations from a set of CMIP5 Global Climate and Earth System Models are investigated. The simulated Arctic sea ice area is compared to passive microwave satellite data from the period 1979-2011. The nine CMIP5 models investigated here reproduce the seasonal cycle and most of them also the year-to-year variability of the Arctic sea ice area in a good way. Most of the models simulate a decreasing September sea ice area, but the trends both under- and overestimate the observed decline for 1980-2007. The southward export of sea ice in the Fram Strait is a major component of the simulated Arctic sea ice area and volume. Annually between 7-17 % of the sea ice covered Arctic Basin is exported in the four models that have ice export available. Three of the four models represent the seasonal cycle and the interannual variance of the ice area export in the Fram Strait reasonably well. The available observations on Arctic sea ice thickness indicate a major thinning since the 1960’s. One of the four models has a mean sea ice thickness comparable to observational estimates in the 1960’s, while the other models have a thickness comparable to today’s thinner sea ice cover. However, none of them are able to reproduce the thinning that has occurred over this time. We have found significant correlation between the Fram Strait ice area export and Arctic sea ice thickness (or volume) on interannual timescales in the four models. This indicates that an increase in ice area export leads a decrease in the sea ice thickness (or volume) one year later. Looking at ice volume export, instead of area export, there also appears a significant correlation – the more intuitive – where thicker Arctic sea ice leads higher Fram Strait ice volume export. A relationship between the mean ice area export and the mean Arctic sea ice thickness north of Fram Strait is found in three of the four models: high ice area export produces thin sea ice, and vice versa. Estimated Fram Strait ice area export has increased with ~5% per decade for the period 1957-2010. The correlations and export-thickness relationship found here suggest that if the models had captured the increased ice area export, more of the observed thinning would also be reproduced.