It's not only the Arctic sea ice that has melted this year. An almost unprecedented 97% of the Greenland ice also melted. This is not an actual catastrophe. It's only the surface that's melted (the ice sheet is up to two miles thick) and it has happened before.
But it is very rare. It happens about once in 150 years. The last time the melting reached Summit Station was 1889!
The reasons are perhaps more worrying than the simple fact. Thomas Mote of the University of Georgia blames the melting on the presence of a pocket of warm air over Greenland. In most years such pockets move away fairly quickly but this year has seen blocked weather systems so this year in stayed put.
Since these blocked weather systems are themselves attributed to climate change what we have here is another positive feedback effect: Global warming => blocking => local warming => melting => reduced albedo => warming.
If we get blocked weather systems next year - itself not unlikely - then we may have to throw away that 'once in 150 years' stuff.
The effects of increased surface melting may go beyond a simple loss of surface ice. When surface water enters crevasses it may lubricate the bottom of the icesheet and accelerate the movement of glaciers. More positive feedback.