Greenland ice melting at an unprecedented rate

The Greenland ice sheet on July 8, below left, and four days later on the right. In the image, the areas classified as 'probable melt' (light pink) correspond to those sites where at least one satellite detected surface melting. The areas classified as 'melt' (dark pink) correspond to sites where two or three satellites detected surface melting:

Photo: NASA

Is it global warming or just a cyclical heatwave event that happens every 150 years?
http://news.nationalgeographic.com/news/2012/07/120725-greenland-ice-sheet-melt-satellites-nasa-space-science/  Scientists are somewhat baffled and can't yet determine if this is a natural, very rare event or one triggered by man-made global warming. They do know that the edges of Greenland's ice sheets have been thinning due to climate change but this summer in Greenland has been freakishly warm so far, due to high pressure systems that parked over the island bringing warm clear weather that melts ice and snow. This is similar to the high pressure systems over the American Midwest which have brought record-breaking heat and drought.