The volume of sea ice in the Arctic has declined sharply in recent decades, as shown in this display. April, which is at the end of the Arctic winter, is still the month with the greatest volume of sea ice, but the total has declined by almost half since 1979. The volume of sea ice in January (midwinter) has dropped by more than half. And in September, at the end of summer, almost no sea ice remains. This graph, sometimes called the "Arctic death spiral," is based on monthly measurements of sea ice from January 1979 to June 2014.
(Original illustration © Andy Lee Robinson, modified by Jack Cook, WHOI)