One way to gauge the amount of ice in the Arctic is to look at the average age of the ice. From the NASA Scientific Visualization Studio, the map above shows the estimated age of ice on a monthly basis, going back to 1984:
One significant change in the Arctic region in recent years has been the rapid decline in perennial sea ice. Perennial sea ice, also known as multi-year ice, is the portion of the sea ice that survives the summer melt season. Perennial ice may have a life-span of nine years or more and represents the thickest component of the sea ice; perennial ice can grow up to four meters thick. By contrast, first year ice that grows during a single winter is generally at most two meters thick.