So only the intercontinental (undersea) connections are vulnerable. Hmmmm, what if...

I was a country that didn't want any site hosted in another ("competing") country being shown in my country?
I want to disrupt overseas financial transactions, either for the fuck of it or just to bug a specific country/group of countries?
I want to see the digital world burn and wreac havoc, again, for the fuck of it or with a specific goal?

Then this phenomenon could be a great excuse/cover up for the things done.
The plot thickens...

What if I forced several countries into using, let's say, certain figherjets totally dependant on a global network to function well and also be controllable via said network?
Or, even better, have nuclear weapons stashed around the world, totally controllable via digital communications after an upgrade I just realised?

The things that can go wrong with a solar superstorm as an excuse.

Oooh, what a world we live in: on one hand it is wonderful to the n-th degree, on the other hand it is so ridden with devious people that totally would and could make formerly mentioned "assumptions" happen. All it takes is one or more lunatics, completely driven by power hunger, money or some imbecelic (read: political) world view.

Seems unlikely that conductors under the sea, made of salty conductive water, would be an issue. The power grid composed of overhead transmission lines on the other hand.

This overlooks the bigger problem; devastation of the power grid in a Carrington-level event. Who cares if you can't tweet or update your facebook when you don't have electricity to keep the food in your fridge cold, and neither do the stores. Generators will run out of fuel. No gas pumps work, so no replenishment and no deliveries to the stores. This outage will last for years as the grid gets rebuilt (if it ever does).

Large cities will starve in less than a month. Mass numbers of refugees will flee, but they will find no welcome anywhere.

Back in the days of Usenet, I read a discussion about this subject that estimated well over half of the world population would be dead in 5 years after the event.

Of course, the Yellowstone stratovolcano could erupt, and that could be an extinction-level event.

Happy thoughts.