The Arctic environment is changing more rapidly than most other regions of the world, and the decrease in sea ice cover is one of the most visible consequences of global warming. This strongly increases Arctic amplification of climate warming, and has fundamental consequences for Arctic shipping, oil and gas extraction, ecological systems, and the sustainability of northern communities. However, major knowledge gaps exist in our understanding, predicting, and responding to the present and future changes. Here we present a new project that addresses uncertainties in Arctic sea ice mass balance observations and modelling by intercomparing ice mass balance estimates from different remote sensing approaches and model initiatives, to derive a reconciled sea ice mass estimate as our best knowledge of the present state of the Arctic sea ice cover. By identifying the major uncertainties in observing and predicting ice mass balance change, and by showing their impact, we will develop recommendations for future research, community coordination efforts, and EO missions.

A reconciled estimate of Arctic sea ice mass balance will be derived using data from the most advanced, recent EO missions, namely ESA’s ERS, Envisat, CryoSat and SMOS missions and NASA’s ICESat mission, and state-of-the-art numerical models. Numerous processing methods have been developed and estimates of seasonal and interannual ice volume changes have been published. We will collect these different data sets and apply unified methods when converting freeboard to thickness and then mass over consistent regions and time periods. This will strongly take advantage of improved snow thickness products once produced by another Arctic+ project. Satellite products and models will be validated by means of airborne laser altimetry and electromagnetic data from ESA’s CryoVEx campaigns and NASA’s Operation IceBridge, as well as by in-situ ice mass balance buoys (IMBs) and upward looking sonar (ULS). The validation will focus on key regions of multiyear and first-year ice coverage, in the spring of 2011 and 2014, where the most extensive validation data are available. Longer time series of reconciled ice mass estimates will then be compared with results from previous studies. Satellite products and models will be used mutually to evaluate uncertainties in both approaches. We will show the impact of reconciled sea ice mass estimates on predictions of seasonal and longer-term ice mass changes, sea ice dynamics and deformation, and freshwater fluxes through Fram Strait. Results will lead to a scientific roadmap for the time frame 2017-2021 suggesting further improved processing methods, reconciled estimates, and the development of assimilation systems and optimized EO missions.