In this recent interview, USNORTHCOM Commander General Victor Renuart outlines growing threats across new frontiers - specifically mentioning cyberspace and the Arctic.
A massive cyber attachk remains what I consider one of the ultimate Black Swans (to the extent that you can't predict a Black Swan except in hindsight). Not only is the military highly dependent on cyber-systems, but so are vast swaths of civilian and commercial infrastructure. According to GEN Renuart, U.S. government and industry officials "have some work do in the cyber area." That is a vast understatement.
I'll be quick to resort to science fiction, but what first comes to mind is the Battlestar Galactica scenario - take out the network that ties everything together, everything falls apart quickly. It would also cause a vast crisis of public confidence.
Additionally, GEN Renuart gives the Arctic its due as a site of potential future security interests. Remember, itinerant blogger Hawkeye Havoc wrote about the Russian moves in this area over a year ago, glad to see NORTHCOM is finally getting up to speed.