The vast majority of multi-year ice is lost during the winter, not the summer. Winter winds blow the thick ice out into the North Atlantic where it melts when it contacts warmer water.
Between 1988 and 1996, two thirds of the five year old ice disappeared.
This has lead to a reduction in summer extent, because the ice in the Chukchi and Beaufort Seas is thinner than it was twenty years ago. The reduction from 1988 to 1996 coincided with the highest ENSO period on record. Conveniently for NSIDC, the satellites they cherry-pick were launched just as ENSO went positive. This has allowed them to show a continuous downwards trend in ice extent.
ENSO is dominantly negative since 2008, and the amount of multi-year ice is increasing again.
Alarmists are hysterical about the “record minimum” extent, but it probably is meaningless for the long term.