The importance of knowledge of the Arctic sea ice age is twofold. First, it is an indicator of changing sea ice state together with changing climate: the Arctic sea ice has become thinner and younger during the last decades. Second, accurate knowledge of the sea ice age provides accurate classification of sea ice types such as first-year ice (FYI) and multi-year ice (MYI), which is crucial information for sea ice thickness retrieval from altimeters. This knowledge is necessary for assessment of snow depth and gives an estimate of sea ice density – two parameters used in the hydrostatic equilibrium equation for thickness retrieval. 

Therefore, introducing in this optional proposal the Sea Ice Age as another parameter of the Sea Ice ECV is beneficial. It will not only improve methods for sea ice age retrieval, but it will also bring together two already existing parameters - Sea Ice Drift and Sea Ice Concentration, and contribute to the Sea Ice Thickness project. The outcome of this option will be an improved sea ice age algorithm and sea ice type algorithm selected as the most optimal to be used in the sea ice thickness retrievals. The option will build the European counterpart to the only existing Sea Ice Age product provided by National Snow and Ice Data Center (NSIDC) in the US. It will naturally lead to a “Sea Ice Drift and Age” ECV for the CCI+. In the CCI+ the Antarctic region should also be included, while the suggested option is only focusing on the Arctic. 

The suggested option will run in parallel with the main ESA CCI Sea Ice project (phase II) starting last quarter of 2016 and ending together with the main project in the end of January 2018. The participant organizations are all involved in the main project except the new participant introduced in this option – The Inversion Lab (iLab, Germany), which is also engaged in the Green House Gases (GHG) CCI project.