How long will summer arctic sea ice survive?

It's really hard to predict when we could see ice-free summers in the Arctic, but it could be as soon as in 20 to 40 years

the conditions that made the byzantine empire vulnerable to attacks by the muslin turks were the sack of constantinople by western crusaders, the conquests of the sultanate of rum, presence of rival kingdoms and finally the set up of fiefdoms at the empire which were owned by the ghazis (turkish warriors).