Arctic sea-ice change: a grand challenge of climate science.

The article focuses on changes in arctic sea-ice. Satellite passive microwave (PMW) sensors are cited for estimating sea-ice extent and concentration. Difficulties in assessing uncertainties in sea-ice thickness estimates are explained together with major developments in modeling and the causes of biases in simulated sea-ice extent. The contribution of natural multi-year and decadal climate variability in the rapid decline of the Arctic ice extent and thickness is examined along with the need to develop strategies for optimizing regional projections.