The “age” of the sea ice color-coded below from blue (4 yr) indicates the stability of the ice pack. Ice that has survived several summers is more likely to survive still longer (perhaps because it is thicker, or the sea and air around it is colder). In general, the volume of ice is greater in the old ice. As the percentage of old sea ice drops, the more likely it is that in a subsequent summer the sea in that area will be exposed to the sunlight of the long days of summer. Ice cover throughout the arctic is getting younger (and thinner) providing less of an insulating blanket in winter and less of a reflective cover in summer. There has never been less “old” ice in the arctic than in any time since the satellite monitoring era began. and when all the old ice is gone, only thin ice formed in that winter will be left when spring comes. And it will melt before the next fall sets in.
Ice several inches thick is just as effective an insulator and reflector as ice several meters thick, but it won’t last long enough to do much good.