Sea ice extent and thickness

To get a true picture of the state of the sea ice you have to both evaluate its extent and its volume. This includes the thickness of the ice, which can vary from thin ice to ice that is several meters thick.

The two tabs with maps and associated animations and graphs show:

  • Sea ice extent in the Northern Hemisphere
  • Sea ice thickness and volume in the Northern Hemisphere

The extent of the ice is based on satellite data and the ice thickness and volume is based on model calculations. The two products can thereby supplement each other and give a more nuanced picture of the state of the sea ice cover in the Northern Hemisphere. There can, however, be differences in the position of the ice edge in the two maps, as the model calculations do not always correspond entirely to the satellite sensors’ registration of the ice extent.

The Arctic ice cover grows throughout the winter and peaks in March. The melting takes off in the course of spring, when the sun gains more strength, and in September the extent of ice is typically down to a third of the winter’s maximum extent.

Sea Ice Extent

The map on the left is updated on a daily basis and shows the ice extent in the Northern Hemisphere. The sea ice extent is defined by areas which have at least 15 % ice concentration. The blue markings show coast lines.

The graph on the right shows the yearly variation in ice extent in the Northern Hemisphere, given by the total area with at least 15 % ice concentration. The grey band around the climatological mean value corresponds to plus/minus 1 standard deviation.

The ice concentrations are based on satellite data and are from the Ocean and Sea Ice, Satellite Application Facility project (OSISAF).

Sea Ice Thickness and Volume

The map on the left is updated on a daily basis and shows the sea ice thickness in the Northern Hemisphere. The ice thickness is calculated by the HYCOM-CICE model at DMI. The model includes meteorological and oceanographic data in a 10 x 10 km grid. The meteorological data come from the ECMWF (European Centre for Medium Range Weather Forecast). Ice thickness, concentration and volume are calculated as mean values in every grid cell.

The graph on the right shows the yearly variation of the sea ice volume in the Northern Hemisphere. The ice volume is calculated on from the ice thickness from the HYCOM-CICE model. In every grid cell the volume is calculated as the thickness times the area, and the contributions from all grid cells are then added to give the total volume. The grey band around the climatological mean value corresponds to plus/minus 1 standard deviation.